源码通透-mybatis源码分析以及整合spring过程

秒速五厘米 2022-04-12 21:26 335阅读 0赞

# 源码通透-mybatis源码分析以及整合spring过程 #

--------------------

mybatis源码分析版本：mybaits3 (3.5.0-SNAPSHOT)

mybatis源码下载地址：[https://github.com/mybatis/mybatis-3][https_github.com_mybatis_mybatis-3]

mybatis整合spring的jar版本：mybatis-spring-1.3.2-sources.jar，后使用2.0.0-SNAPSHOT

spring源码版本： 4.2.0.RELEASE

其它相关源码分析文章：[https://github.com/arthur-dy-lee/arthur-dy-lee-note][https_github.com_arthur-dy-lee_arthur-dy-lee-note]

### 文章目录 ###

*  源码通透-mybatis源码分析以及整合spring过程
 *  一、启动时注入spring
 *   *  1.1 springmvc的xml配置方式
     *  1.2 SqlSessionFactoryBean 创建mybatis的SqlSessionFactory。并将\*mapper.xml, dataSource注入到SqlSessionFactory中
     *   *  1.2.1 SqlSessionFactoryBean作用
         *  1.2.2 SqlSessionFactoryBean的继承关系
         *  1.2.3 SqlSessionFactoryBean\#getObject
         *  1.2.4 afterPropertiesSet源码
         *  1.2.5 创建DefaultSqlSessionFactory并返回SqlSessionFactory
     *  1.3 \*Mapper.xml解析 XMLMapperBuilder\#parse
     *   *  1.3.1 XMLMapperBuilder\#configurationElement
         *  1.3.2 XMLLanguageDriver
         *  1.3.3 XMLMapperBuilder\#bindMapperForNamespace
         *  1.3.4 configuration\#addMapper\#
     *  1.4 通过MapperScannerConfigurer，将\*mapper.java注入到spring容器中
     *   *  1.4.1 MapperScannerConfigurer作用
         *  1.4.2 MapperScannerConfigurer继承关系
         *  1.4.3 postProcessBeanDefinitionRegistry源码
         *   *  ClassPathMapperScanner\#processBeanDefinitions作用是重新组装BeanDefinitions
     *  1.5 调用MapperFactoryBean\#getObject
     *   *  1.5.1 \`MapperFactoryBean\`的继承结构
         *  1.5.2 SqlSessionTemplate初始化
         *  1.5.3 实例化栈信息打印(创建MapperFactoryBean)
         *  1.5.4 初始化栈信息，即调用MapperFactoryBean\#getObject的栈过程
         *  1.5.5 getObject内容分析
 *  二、调用前的拦截器工作
 *   *  2.1 简介做准备工作
     *  2.2 SqlSessionTemplate创建时，加入拦截器SqlSessionInterceptor
     *  2.3 SqlSessionIntercepteor
     *  2.3 SqlSession
     *   *  2.3.1 SqlSession类继承结构
         *  2.3.2 DefaultSqlSession
         *  2.3.3 SqlSessionUtils\#getSqlSession
     *  2.3 DefaultSqlSessionFactory创建事务、SqlSession、Executor
     *  2.4 Executor执行器介绍
     *   *  2.4.1 SimpleExecutor类结构
 *  三、调用过程详解
 *   *  3.1 原生mybatis创建和执行SqlSession的流程示例
     *  3.2 spring调用mybatis过程栈打印
     *  
     *  3.3 MapperProxy 代理Mapper执行
     *  3.4 MapperMethod\#execute
     *   *  3.4.1 MapperMethod\#execute
         *  3.4.2 executeForMany
     *  3.5 SqlSessionTemplate\#selectList
     *  3.5 SqlSessionInterceptor\#invoke
     *  3.7 DefaultSqlSession\#selectList
     *  3.8 CachingExecutor\#query
     *  3.9 SimpleExecutor
     *   *  3.9.1 BaseExecutor\#query
         *  3.9.2 BaseExecutor\#queryFromDatabase
         *  3.9.3 SimpleExecutor\#doQuery
         *  3.9.4 SimpleExecutor\#prepareStatement
     *  3.10 RoutingStatementHandler\#query
     *  3.11 PreparedStatementHandler\#query
 *  四、MyBatis核心构件
 *  五、事务
 *   *  5.1 mybatis-spring的Transaction准备阶段
     *  5.2 mybatis-spring创建SqlSession，并交由spring去得到connection
     *   *  5.2.2 openSession 时创建mybatis事务
         *  5.2.3 保存前当sqlSession，创建并注册事务同步器。
         *  5.2.4 SpringManagedTransaction.getConnection()取出当前connection
         *   *  SpringManagedTransaction\#openConnection
         *  5.2.5 交由spring根据dataSource去创建Connection
     *  5.3 spring事务调用
     *   *  5.3.1 执行过程摘要
         *   *  \*\*invokeWithinTransaction\*\*
         *  5.3.2 执行目标方法(\`Service.\*methoad()\`)前的CGLIB代理拦截器调用
         *   *  创建\`PlatformTransactionManager(DataSourceTransactionManager)\`，并为\`DataSourceTransactionManager\`的属性\`dataSoucre\`赋值
             *  CGLIB代理拦截器栈调用过程
         *  
         *  5.3.3 执行目标方法(\`Service.\*methoad()\`)
         *  5.3.4 执行目标方法(\`Service.\*methoad()\`)后的CGLIB代理拦截器调用：commit提交
         *   *  commit真正提交栈信息打印
             *  DataSourceTransactionManager\#doCommit 真正提交
             *  真正提交前的预提交
             *   *  TransactionSynchronizationUtils\#triggerBeforeCommit
                 *  TransactionSynchronizationUtils\#triggerBeforeCompletion
 *  六 spring事务调用总结
 *   *  6.1 调用
 *  七、 插一段初始化执行顺序
 *  八、其它补充
 *   *  8.1 Mapper接口对应的bean在容器中的数量

# 一、启动时注入spring #

--------------------

## 1.1 springmvc的xml配置方式 ##

在springmvc中我们常这样配置

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="mapperLocations" value="classpath*:com/paincupid/springmvc/persistence/*.xml" />
        <property name="typeAliasesPackage" value="com.paincupid.springmvc.domain" />
    </bean>
    
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.paincupid.springmvc.persistence" />
    </bean>

可以通过mybatis-spring-1.3.2-sources.jar下载源码看2个类：

> org.mybatis.spring.SqlSessionFactoryBean

SqlSessionFactoryBean负责创建mybatis的SqlSessionFactory。并将\*mapper.xml, dataSource注入到SqlSessionFactory中。

> org.mybatis.spring.mapper.MapperScannerConfigurer

MapperScannerConfigurer负责扫描装载dal的java文件到spring容器中。

## 1.2 SqlSessionFactoryBean 创建mybatis的SqlSessionFactory。并将\*mapper.xml, dataSource注入到SqlSessionFactory中 ##

在基本的(纯的，不与spring整合的) MyBatis 中,session 工厂可以使用 SqlSessionFactoryBuilder 来创建。而在 MyBatis-Spring 中,则使用 SqlSessionFactoryBean 来替代。

### 1.2.1 SqlSessionFactoryBean作用 ###

{@code FactoryBean} that creates an MyBatis {@code SqlSessionFactory}.
    This is the usual way to set up a shared MyBatis {@code SqlSessionFactory} in a Spring application context;
    the SqlSessionFactory can then be passed to MyBatis-based DAOs via dependency injection. Either {@code DataSourceTransactionManager} or {@code JtaTransactionManager} can be used for transaction demarcation in combination with a {@code SqlSessionFactory}. JTA should be used for transactions which span multiple databases or when container managed transactions (CMT) are being used.

FactoryBean(SqlSessionFactoryBean)创建mybatis的SqlSessionFactory，在spring上下文中，通常用它来装载mybatis；SqlSessionFactory能够通过依赖注入的方式，传到MyBatis的dao中。同时，DataSourceTransactionManager或者JtaTransactionManager与SqlSessionFactory组合进行事务管理。JTA应该用于跨多个数据库的事务或使用容器管理事务(CMT) 。

### 1.2.2 SqlSessionFactoryBean的继承关系 ###

![SqlSessionFactoryBean.png][]

1、实现FactoryBean接口，FactoryBean用于创建复杂对象时使用，通过getObject对外提供SqlSessionFactory实例。

2、实现InitializingBean，在spring启动初始化时执行`afterPropertiesSet()`方法。

### 1.2.3 SqlSessionFactoryBean\#getObject ###

在一般的 MyBatis-Spring 用法中, 你不需要直接使用 SqlSessionFactoryBean 或和其对应的 SqlSessionFactory。相反,session 工厂将会被注入到 MapperFactoryBean 或其它扩 展了 SqlSessionDaoSupport 的 DAO中。

通过FacotryBean.getObject提供DefaultSqlSessionFactory对象实例

返回之前创建的DefaultSqlSessionFactory，这里可以看到**DefaultSqlSessionFactory只会被初始化一次**。

SqlSessionFactoryBean\#getObject

@Override
    public SqlSessionFactory getObject() throws Exception { 
      if (this.sqlSessionFactory == null) { 
        afterPropertiesSet();
      }
    
      return this.sqlSessionFactory;
    }

### 1.2.4 afterPropertiesSet源码 ###

初始化sqlSessionFactory，相当于，先组装和注册configuration，将configuration传给sqlSessionFactory ：

> sqlSessionFactory = new DefaultSqlSessionFactory(configuration);

@Override
    public void afterPropertiesSet() throws Exception { 
      notNull(dataSource, "Property 'dataSource' is required");
      notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
      state((configuration == null && configLocation == null) || !(configuration != null && configLocation != null),
                "Property 'configuration' and 'configLocation' can not specified with together");
    
      this.sqlSessionFactory = buildSqlSessionFactory();
    }

buildSqlSessionFactory

/** * Build a {@code SqlSessionFactory} instance. * * The default implementation uses the standard MyBatis {@code XMLConfigBuilder} API to build a * {@code SqlSessionFactory} instance based on an Reader. * Since 1.3.0, it can be specified a {@link Configuration} instance directly(without config file). * * @return SqlSessionFactory * @throws IOException if loading the config file failed */
    protected SqlSessionFactory buildSqlSessionFactory() throws IOException { 
    
    Configuration configuration;
    
    XMLConfigBuilder xmlConfigBuilder = null;
    if (this.configuration != null) { 
      configuration = this.configuration;
      if (configuration.getVariables() == null) { 
    	configuration.setVariables(this.configurationProperties);
      } else if (this.configurationProperties != null) { 
    	configuration.getVariables().putAll(this.configurationProperties);
      }
    } else if (this.configLocation != null) { 
      xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
      configuration = xmlConfigBuilder.getConfiguration();
    } 
    //为configuration的属性赋值以及注册一些东西.....
    
    
    if (xmlConfigBuilder != null) { 
      try { 
    	//解析xml文件 
    	xmlConfigBuilder.parse();
    	//.... 
    }
    
    if (this.transactionFactory == null) { 
      this.transactionFactory = new SpringManagedTransactionFactory();
    }
    
    configuration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource));
    
    //<property name="mapperLocations" value="classpath*:com/paincupid/springmvc/persistence/*.xml" />
    //解析*mapper.xml
    if (!isEmpty(this.mapperLocations)) { 
      for (Resource mapperLocation : this.mapperLocations) { 
    	if (mapperLocation == null) { 
    	  continue;
    	}
    
    	try { 
          //XMLMapperBuilder解析*Mapper.xml文件中的标签... 
    	  XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
    		  configuration, mapperLocation.toString(), configuration.getSqlFragments());
    	  xmlMapperBuilder.parse();
    	//....
      }
    }
    
    return this.sqlSessionFactoryBuilder.build(configuration);
    }

### 1.2.5 创建DefaultSqlSessionFactory并返回SqlSessionFactory ###

public SqlSessionFactory build(Configuration config) { 
      return new DefaultSqlSessionFactory(config);
    }

## 1.3 \*Mapper.xml解析 XMLMapperBuilder\#parse ##

XMLMapperBuilder\#parse 入口类

public void parse() { 
      if (!configuration.isResourceLoaded(resource)) { 
        configurationElement(parser.evalNode("/mapper")); //<----- 1.3.1
        configuration.addLoadedResource(resource);
        bindMapperForNamespace();//<----- 1.3.3
      }
    
      parsePendingResultMaps();
      parsePendingCacheRefs();
      parsePendingStatements();
    }

### 1.3.1 XMLMapperBuilder\#configurationElement ###

XMLMapperBuilder\#configurationElement

private void configurationElement(XNode context) { 
      try { 
        String namespace = context.getStringAttribute("namespace"); //得到namespace
        if (namespace == null || namespace.equals("")) { 
          throw new BuilderException("Mapper's namespace cannot be empty");
        }
        builderAssistant.setCurrentNamespace(namespace);
        cacheRefElement(context.evalNode("cache-ref"));
        cacheElement(context.evalNode("cache"));
        parameterMapElement(context.evalNodes("/mapper/parameterMap"));
        //处理<resultMap>这类标签，然后再MapperBuilderAssistant类的addResultMap()方法中把每个ResultMap对象加到Configuration对象中的resultMaps属性中（中间会把<resultMap>标签中的每一个子标签封装成ResultMapping对象，然后封装成ResultMap对象，最后put到Configuration对象中，id规则为：namespace+<resultMap>的id属性 ）
        resultMapElements(context.evalNodes("/mapper/resultMap"));
        sqlElement(context.evalNodes("/mapper/sql"));
        buildStatementFromContext(context.evalNodes("select|insert|update|delete"));//<--------
      } catch (Exception e) { 
        throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);
      }
    }

XMLMapperBuilder\#buildStatementFromContext

private void buildStatementFromContext(List<XNode> list) { 
      if (configuration.getDatabaseId() != null) { 
        buildStatementFromContext(list, configuration.getDatabaseId());
      }
      buildStatementFromContext(list, null);
    }

XMLMapperBuilder\#buildStatementFromContext

private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) { 
      for (XNode context : list) { 
        final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
        try { 
          statementParser.parseStatementNode();
        } catch (IncompleteElementException e) { 
          configuration.addIncompleteStatement(statementParser);
        }
      }
    }

XMLStatementBuilder\#parseStatementNode 解析标签

public void parseStatementNode() { 
      String id = context.getStringAttribute("id");
      String databaseId = context.getStringAttribute("databaseId");
    
      if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) { 
        return;
      }
    
      Integer fetchSize = context.getIntAttribute("fetchSize");
      Integer timeout = context.getIntAttribute("timeout");
      String parameterMap = context.getStringAttribute("parameterMap");
      String parameterType = context.getStringAttribute("parameterType");
      Class<?> parameterTypeClass = resolveClass(parameterType);
      String resultMap = context.getStringAttribute("resultMap");
      String resultType = context.getStringAttribute("resultType");
      String lang = context.getStringAttribute("lang");
      LanguageDriver langDriver = getLanguageDriver(lang);
    
      Class<?> resultTypeClass = resolveClass(resultType);
      String resultSetType = context.getStringAttribute("resultSetType");
      StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
      ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
    
      String nodeName = context.getNode().getNodeName();
      SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
      boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
      boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
      boolean useCache = context.getBooleanAttribute("useCache", isSelect);
      boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);
    
      // Include Fragments before parsing
      XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
      includeParser.applyIncludes(context.getNode());
    
      // Parse selectKey after includes and remove them.
      processSelectKeyNodes(id, parameterTypeClass, langDriver);
      
      // <---------------------- 
      // Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
      SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
      String resultSets = context.getStringAttribute("resultSets");
      String keyProperty = context.getStringAttribute("keyProperty");
      String keyColumn = context.getStringAttribute("keyColumn");
      KeyGenerator keyGenerator;
      String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
      keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
      if (configuration.hasKeyGenerator(keyStatementId)) { 
        keyGenerator = configuration.getKeyGenerator(keyStatementId);
      } else { 
        keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
            configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
            ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
      }
    
      builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
          fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
          resultSetTypeEnum, flushCache, useCache, resultOrdered, 
          keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
    }

下面看：

> SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);

### 1.3.2 XMLLanguageDriver ###

XMLLanguageDriver\#createSqlSource

@Override
    public SqlSource createSqlSource(Configuration configuration, XNode script, Class<?> parameterType) { 
      XMLScriptBuilder builder = new XMLScriptBuilder(configuration, script, parameterType);
      return builder.parseScriptNode();
    }

XMLLanguageDriver\#parseScriptNode

public SqlSource parseScriptNode() { 
      //解析动态标签比如if、foreach...每个动态标签都会有不同的handel去处理，如果动态标签嵌套动态标签的话，还会递归去调用parseDynamicTags(XNode node)方法，每一个标签封装成一个sqlNode 
      List<SqlNode> contents = parseDynamicTags(context);
      //封装一个MixedSqlNode对象，有一个apply方法，用户解析动态sql 
      MixedSqlNode rootSqlNode = new MixedSqlNode(contents);
      SqlSource sqlSource = null;
      if (isDynamic) { 
        sqlSource = new DynamicSqlSource(configuration, rootSqlNode);
      } else { 
        sqlSource = new RawSqlSource(configuration, rootSqlNode, parameterType);
      }
      return sqlSource;
    }

到这里整个`configurationElement(XNode context)`方法就分析完了。

### 1.3.3 XMLMapperBuilder\#bindMapperForNamespace ###

private void bindMapperForNamespace() { 
      String namespace = builderAssistant.getCurrentNamespace();
      if (namespace != null) { 
        Class<?> boundType = null;
        try { 
          boundType = Resources.classForName(namespace);
        } catch (ClassNotFoundException e) { 
          //ignore, bound type is not required
        }
        if (boundType != null) { 
          if (!configuration.hasMapper(boundType)) { 
            // Spring may not know the real resource name so we set a flag
            // to prevent loading again this resource from the mapper interface
            // look at MapperAnnotationBuilder#loadXmlResource
            configuration.addLoadedResource("namespace:" + namespace);
            configuration.addMapper(boundType);
          }
        }
      }
    }

看代码`configuration.addMapper(boundType);`

### 1.3.4 configuration\#addMapper\# ###

将MapperProxyFactory放到knownMappers，后面会通过MapperRegistry\#getMapper重新取出来，可以看1.5.5 getObject时取。knownMappers里面放的都是自己工程中的\*Mapper.xml

public <T> void addMapper(Class<T> type) { 
      mapperRegistry.addMapper(type);
    }

MapperRegistry\#addMapper

public <T> void addMapper(Class<T> type) { 
      if (type.isInterface()) { 
        if (hasMapper(type)) { 
          throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
        }
        boolean loadCompleted = false;
        try { 
          // 将MapperProxyFactory放到knownMappers，后面会通过MapperRegistry#getMapper重新取出来，可以看1.5.5 getObject时取。
          knownMappers.put(type, new MapperProxyFactory<T>(type)); 
          // It's important that the type is added before the parser is run
          // otherwise the binding may automatically be attempted by the
          // mapper parser. If the type is already known, it won't try.
          MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
          parser.parse();
          loadCompleted = true;
        } finally { 
          if (!loadCompleted) { 
            knownMappers.remove(type);
          }
        }
      }
    }

## 1.4 通过MapperScannerConfigurer，将\*mapper.java注入到spring容器中 ##

### 1.4.1 MapperScannerConfigurer作用 ###

将\*mapper.java注入到spring容器中，在组装mapper的BeanDefinition的时候，会将`sqlSessionFactory`、`sqlSessionTemplate`一起放到BeanDefinition中。

### 1.4.2 MapperScannerConfigurer继承关系 ###

![MapperScannerConfigurer.png][]

1、实现`postProcessBeanDefinitionRegistry`接口，它实际是一个`BeanFactoryPostProcessor`，它会调用`BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)`方法。

2、实现`InitializingBean`，调用`afterPropertiesSet()`，在`MapperScannerConfigurer`中，只是用它用做校验

@Override
    public void afterPropertiesSet() throws Exception { 
      notNull(this.basePackage, "Property 'basePackage' is required");
    }

3、实现`ApplicationContextAware`接口，执行ApplicationContextAware.setApplicationContext(ApplicationContext applicationContext)\`方法。用于将applicationContext传过来。

@Override
    public void setApplicationContext(ApplicationContext applicationContext) { 
      this.applicationContext = applicationContext;
    }

4、实现`BeanNameAware` 接口，为bean命名

@Override
    public void setBeanName(String name) { 
        this.beanName = name;
    }

这里主要看`postProcessBeanDefinitionRegistry`方法

### 1.4.3 postProcessBeanDefinitionRegistry源码 ###

@Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) { 
      if (this.processPropertyPlaceHolders) { 
        processPropertyPlaceHolders();
      }
    
      ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
      scanner.setAddToConfig(this.addToConfig);
      scanner.setAnnotationClass(this.annotationClass);
      scanner.setMarkerInterface(this.markerInterface);
      scanner.setSqlSessionFactory(this.sqlSessionFactory);
      scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
      scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
      scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
      scanner.setResourceLoader(this.applicationContext);
      scanner.setBeanNameGenerator(this.nameGenerator);
      scanner.registerFilters();
      //<------ 
      scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
    }

ClassPathMapperScanner\#scan

public int scan(String... basePackages) { 
       int beanCountAtScanStart = this.registry.getBeanDefinitionCount();
    
       doScan(basePackages);
    
       // Register annotation config processors, if necessary.
       //如果有注解，也一起注册到容器中 
       if (this.includeAnnotationConfig) { 
          AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
       }
    
       return (this.registry.getBeanDefinitionCount() - beanCountAtScanStart);
    }

ClassPathMapperScanner\#doScan

public Set<BeanDefinitionHolder> doScan(String... basePackages) { 
      //会调用父类的ClassPathBeanDefinitionScanner。doScan方法 <-----
      Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
    
      if (beanDefinitions.isEmpty()) { 
        logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
      } else { 
        //<-----
        processBeanDefinitions(beanDefinitions);
      }
      return beanDefinitions;
    }

> public class ClassPathMapperScanner extends ClassPathBeanDefinitionScanner

`ClassPathBeanDefinitionScanner`是`spring-context`包下的类，直接使用spring的类去进行\*mapper.java的注册。  
`ClassPathBeanDefinitionScanner`的包全路径为：  
org.springframework.context.annotation.ClassPathBeanDefinitionScanner

ClassPathBeanDefinitionScanner\#doScan源码

protected Set<BeanDefinitionHolder> doScan(String... basePackages) { 
       Assert.notEmpty(basePackages, "At least one base package must be specified");
       Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();
       for (String basePackage : basePackages) { 
          Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
          for (BeanDefinition candidate : candidates) { 
             ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
             candidate.setScope(scopeMetadata.getScopeName());
             String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
             if (candidate instanceof AbstractBeanDefinition) { 
                postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
             }
             if (candidate instanceof AnnotatedBeanDefinition) { 
                AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
             }
             if (checkCandidate(beanName, candidate)) { 
                BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
                definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
                beanDefinitions.add(definitionHolder);
                registerBeanDefinition(definitionHolder, this.registry);
             }
          }
       }
       return beanDefinitions;
    }

这里只看一下`doScan()`的结果。`Set<BeanDefinitionHolder> beanDefinitions`断点，我们可以看到包扫描得的mapper，当然现在还是beanDefinition的形式。

![beanDefinitions.png][]

`processBeanDefinitions`方法

#### ClassPathMapperScanner\#processBeanDefinitions作用是重新组装BeanDefinitions ####

1、将`MapperFactoryBean`放到`beanDefinitions`。将`beanDefinitions`的`beanClass`设置为`MapperFactoryBean`。mapper接口是原始的bean，但`MapperFactoryBean`是真正的bean。也就是说注册到spring容器中的是`MapperFactoryBean`。

> the mapper interface is the original class of the bean. but, the actual class of the bean is MapperFactoryBean

2、将`sqlSessionFactory`放到`beanDefinitions`

3、将`sqlSessionTemplate`放到`beanDefinitions`

private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) { 
      GenericBeanDefinition definition;
      for (BeanDefinitionHolder holder : beanDefinitions) { 
        definition = (GenericBeanDefinition) holder.getBeanDefinition();
    
        // the mapper interface is the original class of the bean
        // but, the actual class of the bean is MapperFactoryBean 
        definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
        //实际类为 MapperFactoryBean <------------
        definition.setBeanClass(this.mapperFactoryBean.getClass());
    
        definition.getPropertyValues().add("addToConfig", this.addToConfig);
    
        boolean explicitFactoryUsed = false;
        if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) { 
          //注册sqlSessionFactory <--------- 
          definition.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
          explicitFactoryUsed = true;
        } else if (this.sqlSessionFactory != null) { 
          //注册sqlSessionFactory <--------- 
          definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
          explicitFactoryUsed = true;
        }
    
        if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) { 
          //注册 sqlSessionTemplate <------------- 
          definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
          explicitFactoryUsed = true;
        } else if (this.sqlSessionTemplate != null) { 
          //注册 sqlSessionTemplate <-------------
          definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
          explicitFactoryUsed = true;
        }
    
        if (!explicitFactoryUsed) { 
          //将beanDefinition设为按类型注入
          definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
        }
      }
    }

## 1.5 调用MapperFactoryBean\#getObject ##

在将`**Mapper`变成`MapperFactoryBean`组装成`beanDefinition`注册到容器beanFactory容器后，会继续执行spring的`refresh()`中的`finishBeanFactoryInitialization`方法，此方法的作用是：完成spring上下文的初始化，初始化beanFactory剩余的单例bean。这时，会实例化`MapperFactoryBean`。

### 1.5.1 `MapperFactoryBean`的继承结构 ###

`MapperFactoryBean`也是一个FactoryBean，并且间接实现了InitializingBean接口。

![Image 1][]

`DaoSupport.afterPropertiesSet()`

此处用模板板式，2个抽象方法：`checkDaoConfig()`和`initDao()`，先执行`checkDaoConfig()`，后执行`initDao()`

@Override
    public final void afterPropertiesSet() throws IllegalArgumentException, BeanInitializationException { 
       // Let abstract subclasses check their configuration.
       checkDaoConfig();
    
       // Let concrete implementations initialize themselves.
       try { 
          initDao();
       }
       catch (Exception ex) { 
          throw new BeanInitializationException("Initialization of DAO failed", ex);
       }
    }
    protected abstract void checkDaoConfig() throws IllegalArgumentException;
    
    protected void initDao() throws Exception { }

### 1.5.2 SqlSessionTemplate初始化 ###

**SqlSessionTemplate，是spring连接mybatis的模板类，是由spring负责生成的**

`MapperFactoryBean`继承`SqlSessionDaoSupport`，`SqlSessionDaoSupport`使用构造函数，创建`SqlSessionTemplate`对象，并将它保存到`sqlSession`属性中。

public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) { 
      if (!this.externalSqlSession) { 
        this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
      }
    }

SqlSessionTemplate 3个构造函数调用过程

public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory) { 
      this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType());
    }

public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType) { 
      this(sqlSessionFactory, executorType,
          new MyBatisExceptionTranslator(
              sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(), true));
    }

在SqlSessionTemplate初始化的时候，就将拦截器`SqlSessionInterceptor`放进去。

public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
        PersistenceExceptionTranslator exceptionTranslator) { 
    
      notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
      notNull(executorType, "Property 'executorType' is required");
    
      this.sqlSessionFactory = sqlSessionFactory;
      this.executorType = executorType;
      this.exceptionTranslator = exceptionTranslator;
      this.sqlSessionProxy = (SqlSession) newProxyInstance(
          SqlSessionFactory.class.getClassLoader(),
          new Class[] {  SqlSession.class },
          new SqlSessionInterceptor());
    }

### 1.5.3 实例化栈信息打印(创建MapperFactoryBean) ###

如下图所示：

![MapperFactoryBean-instance.png][]

可以看到最后是通过反射，调用构造函数来实现`MapperFactoryBean`的实例化。

看一下`java.lang.reflect.Constructor.newInstance()`

public T newInstance(Object ... initargs)
        throws InstantiationException, IllegalAccessException,
               IllegalArgumentException, InvocationTargetException
    { 
        //......
        ConstructorAccessor ca = constructorAccessor;   // read volatile
        if (ca == null) { 
            ca = acquireConstructorAccessor();
        }
        @SuppressWarnings("unchecked")
        T inst = (T) ca.newInstance(initargs);
        return inst;
    }

这些执行步骤只是用反射把对象new出来，但还没有完成对象实例，下面还会进行对象的初始化。

### 1.5.4 初始化栈信息，即调用MapperFactoryBean\#getObject的栈过程 ###

public T getObject() throws Exception { 
      return getSqlSession().getMapper(this.mapperInterface); //getSqlSession()是SqlSessionTemplate
    }

备注：getSqlSession()`是`SqlSessionTemplate, 上面已讲了SqlSessionTemplate的初始化。

newInstance:47, MapperProxyFactory (org.apache.ibatis.binding)
    newInstance:52, MapperProxyFactory (org.apache.ibatis.binding)
    getMapper:50, MapperRegistry (org.apache.ibatis.binding)
    getMapper:732, Configuration (org.apache.ibatis.session)
    getMapper:318, SqlSessionTemplate (org.mybatis.spring)
    getObject:95, MapperFactoryBean (org.mybatis.spring.mapper)
    doGetObjectFromFactoryBean:168, FactoryBeanRegistrySupport (org.springframework.beans.factory.support)
    getObjectFromFactoryBean:103, FactoryBeanRegistrySupport (org.springframework.beans.factory.support)
    getObjectForBeanInstance:1574, AbstractBeanFactory (org.springframework.beans.factory.support)
    doGetBean:253, AbstractBeanFactory (org.springframework.beans.factory.support)
    getBean:201, AbstractBeanFactory (org.springframework.beans.factory.support)
    doGetBean:274, AbstractBeanFactory (org.springframework.beans.factory.support)
    getBean:196, AbstractBeanFactory (org.springframework.beans.factory.support)
    findAutowireCandidates:1145, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    doResolveDependency:1069, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    resolveDependency:967, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    inject:543, AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement (org.springframework.beans.factory.annotation)
    inject:88, InjectionMetadata (org.springframework.beans.factory.annotation)
    postProcessPropertyValues:331, AutowiredAnnotationBeanPostProcessor (org.springframework.beans.factory.annotation)
    populateBean:1214, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    doCreateBean:543, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    createBean:482, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    getObject:305, AbstractBeanFactory$1 (org.springframework.beans.factory.support)
    getSingleton:230, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support)
    doGetBean:301, AbstractBeanFactory (org.springframework.beans.factory.support)
    getBean:196, AbstractBeanFactory (org.springframework.beans.factory.support)
    findAutowireCandidates:1145, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    doResolveDependency:1069, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    resolveDependency:967, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    inject:543, AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement (org.springframework.beans.factory.annotation)
    inject:88, InjectionMetadata (org.springframework.beans.factory.annotation)
    postProcessPropertyValues:331, AutowiredAnnotationBeanPostProcessor (org.springframework.beans.factory.annotation)
    populateBean:1214, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    doCreateBean:543, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    createBean:482, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    getObject:305, AbstractBeanFactory$1 (org.springframework.beans.factory.support)
    getSingleton:230, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support)
    doGetBean:301, AbstractBeanFactory (org.springframework.beans.factory.support)
    getBean:196, AbstractBeanFactory (org.springframework.beans.factory.support)
    preInstantiateSingletons:772, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    finishBeanFactoryInitialization:834, AbstractApplicationContext (org.springframework.context.support)

在调用过程中，我们可以看一下

AbstractBeanFactory\#getObjectForBeanInstance 如果是普通beanInstance或者beanName前有&符号，则返回它；如果是FactoryBean类型的实例，则返回FactoryBean.getObject。

protected Object getObjectForBeanInstance(
          Object beanInstance, String name, String beanName, RootBeanDefinition mbd) { 
    
       // Don't let calling code try to dereference the factory if the bean isn't a factory.
       if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) { 
          throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
       }
    
       // Now we have the bean instance, which may be a normal bean or a FactoryBean.
       // If it's a FactoryBean, we use it to create a bean instance, unless the
       // caller actually wants a reference to the factory.
       // <-------------- 
       if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) { 
          return beanInstance;
       }
    
       Object object = null;
       if (mbd == null) { 
          object = getCachedObjectForFactoryBean(beanName);
       }
       if (object == null) { 
          // Return bean instance from factory.
          FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
          // Caches object obtained from FactoryBean if it is a singleton.
          if (mbd == null && containsBeanDefinition(beanName)) { 
             mbd = getMergedLocalBeanDefinition(beanName);
          }
          boolean synthetic = (mbd != null && mbd.isSynthetic());
          object = getObjectFromFactoryBean(factory, beanName, !synthetic);
       }
       return object;
    }

看一下BeanFactoryUtils.isFactoryDereference源码：

public static boolean isFactoryDereference(String name) { 
       //String FACTORY_BEAN_PREFIX = "&"; 
       return (name != null && name.startsWith(BeanFactory.FACTORY_BEAN_PREFIX));
    }

FactoryBeanRegistrySupport\#doGetObjectFromFactoryBean，会调用FactoryBean.getObject方法。

/** * Obtain an object to expose from the given FactoryBean. * @param factory the FactoryBean instance * @param beanName the name of the bean * @return the object obtained from the FactoryBean * @throws BeanCreationException if FactoryBean object creation failed * @see org.springframework.beans.factory.FactoryBean#getObject() */
    private Object doGetObjectFromFactoryBean(final FactoryBean<?> factory, final String beanName)
          throws BeanCreationException { 
    
       Object object;
       try { 
          if (System.getSecurityManager() != null) { 
             AccessControlContext acc = getAccessControlContext();
             try { 
                object = AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() { 
                   @Override
                   public Object run() throws Exception { 
                         return factory.getObject();
                      }
                   }, acc);
             }
             catch (PrivilegedActionException pae) { 
                throw pae.getException();
             }
          }
          else { 
             object = factory.getObject();
          }
       }
       // ...
       return object;
    }

### 1.5.5 getObject内容分析 ###

public T getObject() throws Exception { 
      return getSqlSession().getMapper(this.mapperInterface); //getSqlSession()是SqlSessionTemplate
    }

`getSqlSession()`是`SqlSessionTemplate`

是SqlSessionTemplate\#getMapper

public class SqlSessionTemplate implements SqlSession, DisposableBean { 
    
      private final SqlSessionFactory sqlSessionFactory;
      private final ExecutorType executorType;
      private final SqlSession sqlSessionProxy;
      private final PersistenceExceptionTranslator exceptionTranslator;
        
      @Override
      public <T> T getMapper(Class<T> type) { 
        return getConfiguration().getMapper(type, this);
      }
    }

`getConfiguration()`

@Override
    public Configuration getConfiguration() { 
      return this.sqlSessionFactory.getConfiguration();
    }

sqlSessionFactory的值为：DefaultSqlSessionFactory

`DefaultSqlSessionFactory`是`SqlSessionFactory`的实现类。前面springmvc配置xml文件中的`org.mybatis.spring.SqlSessionFactoryBean`，就是用来产生`SqlSessionFactory`，在`SqlSessionFactoryBean`。getObject()`的时候，就会返回一个`DefaultSqlSessionFactory\`。

Configuration\#getMapper

public <T> T getMapper(Class<T> type, SqlSession sqlSession) { 
      return mapperRegistry.getMapper(type, sqlSession);
    }

MapperRegistry\#getMapper

public class MapperRegistry { 
      private final Configuration config;
      private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<Class<?>, MapperProxyFactory<?>>();
    
      public MapperRegistry(Configuration config) { 
        this.config = config;
      }
        
        public <T> T getMapper(Class<T> type, SqlSession sqlSession) { 
          final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
          if (mapperProxyFactory == null) { 
            throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
          }
          try { 
            return mapperProxyFactory.newInstance(sqlSession);
          } catch (Exception e) { 
            throw new BindingException("Error getting mapper instance. Cause: " + e, e);
          }
        }
        
    }

knownMappers会缓存所有的 \*Mapper。此时knownMappers， size = 3里面存的是：

![MapperRegistry.png][]

MapperProxyFactory\#newInstance 通过代理工厂来创建实例。

protected T newInstance(MapperProxy<T> mapperProxy) { 
      return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] {  mapperInterface }, mapperProxy);
    }
    
    public T newInstance(SqlSession sqlSession) { 
      final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
      return newInstance(mapperProxy);
    }

此处 mapperInterface = interface com.paincupid.springmvc.persistence.PersonMapper

后由`MapperProxy`代理`*Mapper`执行，上面返回Mapper的代理类实例`mapperProxy`，在执行时，通过JDK来执行`MapperProxy.invoke`方法。最后getObject得到的是`MapperProxy`。

# 二、调用前的拦截器工作 #

--------------------

## 2.1 简介做准备工作 ##

1、`SqlSessionInterceptor`代理了`SqlSessionTemplate`。在创建`MapperFactoryBean`时，通过构造函数就会创建`SqlSessionInterceptor`，所以在执行`SqlSessionTemplate`时，会被`SqlSessionInterceptor`拦截，然后执行时，真正是通过`DefaultSqlSession`执行。

2、`DefaultSqlSession`持有执行器、configuration。事务保存在执行器中，由执行器执行查询操作。

## 2.2 SqlSessionTemplate创建时，加入拦截器SqlSessionInterceptor ##

## 2.3 SqlSessionIntercepteor ##

托管流程：spring创建了SqlSessionTemplate，在创建SqlSessionTemplate的时候提供了方法拦截器 SqlSessionInterceptor；SqlSessionTemplate实现了SqlSession接口，所以SqlSessionInterceptor会对SqlSessionTemplate中所有SqlSession接口定义的方法进行拦截；也就是说，整合spring之后的crud操作都会经过SqlSessionTemplate类，并且所有crud方法会被SqlSessionInterceptor拦截；最终SqlSessionTemplate通过代理拦截，并且通过SqlSessionHolder实现的sqlsession线程安全和自动新建和释放连接。

使用JDK动态代理，`SqlSessionInterceptor`实现InvocationHandler`接口，在`SqlSessionTemplate\`类中，源码如下：

/** * Proxy needed to route MyBatis method calls to the proper SqlSession got * from Spring's Transaction Manager * It also unwraps exceptions thrown by {@code Method#invoke(Object, Object...)} to * pass a {@code PersistenceException} to the {@code PersistenceExceptionTranslator}. */
    private class SqlSessionInterceptor implements InvocationHandler { 
      @Override
      public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { 
        //getSqlSession很重要，创建了DefaultSqlSession、事务、执行器。事务保存在执行器中， DefaultSqlSession持有执行器、configuration
        SqlSession sqlSession =getSqlSession(
            SqlSessionTemplate.this.sqlSessionFactory,
            SqlSessionTemplate.this.executorType,
            SqlSessionTemplate.this.exceptionTranslator);
        try { 
          //通过sqlSession对象执行真正的crud操作 
          Object result = method.invoke(sqlSession, args);
          if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) { 
            // force commit even on non-dirty sessions because some databases require
            // a commit/rollback before calling close()
            sqlSession.commit(true);
          }
          return result;
        } catch (Throwable t) { 
          Throwable unwrapped = unwrapThrowable(t);
          if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) { 
            // release the connection to avoid a deadlock if the translator is no loaded. See issue #22
            closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
            sqlSession = null;
            Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
            if (translated != null) { 
              unwrapped = translated;
            }
          }
          throw unwrapped;
        } finally { 
          if (sqlSession != null) { 
            closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
          }
        }
      }
    }

## 2.3 SqlSession ##

### 2.3.1 SqlSession类继承结构 ###

![SqlSession.png][]

### 2.3.2 DefaultSqlSession ###

上面的getSession，得到的是DefaultSqlSession。事务保存在执行器中， DefaultSqlSession持有执行器、configuration

public class DefaultSqlSession implements SqlSession { 
    
      private Configuration configuration;
      private Executor executor;
    
      private boolean autoCommit;
      private boolean dirty;
      private List<Cursor<?>> cursorList;
    
      public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) { 
        this.configuration = configuration;
        this.executor = executor;
        this.dirty = false;
        this.autoCommit = autoCommit;
      }
    }

### 2.3.3 SqlSessionUtils\#getSqlSession ###

/** * Gets an SqlSession from Spring Transaction Manager or creates a new one if needed. * Tries to get a SqlSession out of current transaction. If there is not any, it creates a new one. * Then, it synchronizes the SqlSession with the transaction if Spring TX is active and * <code>SpringManagedTransactionFactory</code> is configured as a transaction manager. * * @param sessionFactory a MyBatis {@code SqlSessionFactory} to create new sessions * @param executorType The executor type of the SqlSession to create * @param exceptionTranslator Optional. Translates SqlSession.commit() exceptions to Spring exceptions. * @throws TransientDataAccessResourceException if a transaction is active and the * {@code SqlSessionFactory} is not using a {@code SpringManagedTransactionFactory} * @see SpringManagedTransactionFactory */
    public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) { 
    
      notNull(sessionFactory, NO_SQL_SESSION_FACTORY_SPECIFIED);
      notNull(executorType, NO_EXECUTOR_TYPE_SPECIFIED);
    
      SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);
    
      SqlSession session = sessionHolder(executorType, holder);
      if (session != null) { 
        return session;
      }
    
      if (LOGGER.isDebugEnabled()) { 
        LOGGER.debug("Creating a new SqlSession");
      }
    
      session = sessionFactory.openSession(executorType); //new DefaultSqlSession <-----
    
      registerSessionHolder(sessionFactory, executorType, exceptionTranslator, session);
    
      return session;
    }

## 2.3 DefaultSqlSessionFactory创建事务、SqlSession、Executor ##

在执行`openSessionFromDataSource()`时，会创建

1、执行器`Executor executor = configuration.newExecutor(tx, execType);`

2、创建SqlSession：`new DefaultSqlSession(configuration, executor, autoCommit);`

3、创建Transaction ：`tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);`

DefaultSqlSessionFactory\#openSession

`openSession`创建了DefaultSqlSession、事务、执行器。事务保存在执行器中， DefaultSqlSession持有执行器、configuration

@Override
    public SqlSession openSession(ExecutorType execType) { 
      return openSessionFromDataSource(execType, null, false);
    }

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) { 
      Transaction tx = null;
      try { 
        final Environment environment = configuration.getEnvironment();
        final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
        //创建事务 
        tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
        //创建执行器 
        final Executor executor = configuration.newExecutor(tx, execType);
        return new DefaultSqlSession(configuration, executor, autoCommit); // <-----------
      } catch (Exception e) { 
        closeTransaction(tx); // may have fetched a connection so lets call close()
        throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
      } finally { 
        ErrorContext.instance().reset();
      }
    }

`configuration.newExecutor(tx, execType);`根据类型创建执行器。

## 2.4 Executor执行器介绍 ##

Executor是MyBatis执行器，是MyBatis 调度的核心，负责SQL语句的生成和查询缓存的维护 。

Configuration\#newExecutor 会根据`ExecutorType`创建不同的`Executor`: `SimpleExecutor`、`BatchExecutor`、`ReuseExecutor`

Executor代表执行器，他来调度StatementHandler、ParameterHandler、ResultHandler等来执行SQL；

Configuration\#newExecutor

public Executor newExecutor(Transaction transaction, ExecutorType executorType) { 
      executorType = executorType == null ? defaultExecutorType : executorType;
      executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
      Executor executor;
      if (ExecutorType.BATCH == executorType) { 
        executor = new BatchExecutor(this, transaction);
      } else if (ExecutorType.REUSE == executorType) { 
        executor = new ReuseExecutor(this, transaction);
      } else { 
        executor = new SimpleExecutor(this, transaction);
      }
      if (cacheEnabled) { 
        //new CachingExecutor, 在本例中，executor = new SimpleExecutor 所以后面调用的是先是CachingExecutor，后是SimpleExecutor。
        executor = new CachingExecutor(executor);
      }
      //可追加拦截器 
      executor = (Executor) interceptorChain.pluginAll(executor);
      return executor;
    }

在本例中，`executor = new SimpleExecutor` 所以后面调用的是先是`CachingExecutor`，后是`SimpleExecutor`。

`executor = (Executor) interceptorChain .pluginAll(executor);`表明可追加拦截器。

用户可以自定义拦截器，可以实现Interceptor接口，然后封装插件，比如分页插件。

public class InterceptorChain { 
    
      private final List<Interceptor> interceptors = new ArrayList<Interceptor>();
    
      public Object pluginAll(Object target) { 
        for (Interceptor interceptor : interceptors) { 
          target = interceptor.plugin(target);
        }
        return target;
      }
    
      public void addInterceptor(Interceptor interceptor) { 
        interceptors.add(interceptor);
      }
      
      public List<Interceptor> getInterceptors() { 
        return Collections.unmodifiableList(interceptors);
      }
    
    }

### 2.4.1 SimpleExecutor类结构 ###

![SimpleExecutor.png][]

SimpleExecutor\#doQuery

这个和传统的JDBC调用就没什么区别了，先建立链接，再创建Statement，然后再执行，最后返回结果集。

@Override
    public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException { 
      Statement stmt = null;
      try { 
        Configuration configuration = ms.getConfiguration();
        //创建Statement 
        StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
        stmt = prepareStatement(handler, ms.getStatementLog());
        return handler.<E>query(stmt, resultHandler);
      } finally { 
        closeStatement(stmt);
      }
    }

# 三、调用过程详解 #

--------------------

## 3.1 原生mybatis创建和执行SqlSession的流程示例 ##

SqlSession sqlSession = null;
    try { 
        sqlSession = sqlSessionFactory.openSession();
        sqlSession.insert("cn.jarjar.dao.BlogMapper.insertBlog", blog);
        sqlSession.commit(true)
    } catch (Exception e) { 
        e.printStackTrace();
        sqlSession.rollback(true);
    } finally {  
        sqlSession.close();
    }

## 3.2 spring调用mybatis过程栈打印 ##

栈显示的是PersionMapper.list()方法为示例的。

query:62, PreparedStatementHandler (org.apache.ibatis.executor.statement)
    query:79, RoutingStatementHandler (org.apache.ibatis.executor.statement)
    doQuery:63, SimpleExecutor (org.apache.ibatis.executor)
    queryFromDatabase:324, BaseExecutor (org.apache.ibatis.executor)
    query:156, BaseExecutor (org.apache.ibatis.executor)
    query:109, CachingExecutor (org.apache.ibatis.executor)
    query:83, CachingExecutor (org.apache.ibatis.executor)
    selectList:148, DefaultSqlSession (org.apache.ibatis.session.defaults)
    selectList:141, DefaultSqlSession (org.apache.ibatis.session.defaults)
    invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
    invoke:62, NativeMethodAccessorImpl (sun.reflect)
    invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
    invoke:497, Method (java.lang.reflect)
    invoke:433, SqlSessionTemplate$SqlSessionInterceptor (org.mybatis.spring)
    selectList:-1, $Proxy11 (com.sun.proxy)
    selectList:230, SqlSessionTemplate (org.mybatis.spring)
    executeForMany:137, MapperMethod (org.apache.ibatis.binding)
    execute:75, MapperMethod (org.apache.ibatis.binding)
    invoke:59, MapperProxy (org.apache.ibatis.binding)
    listPerson:-1, $Proxy20 (com.sun.proxy)
    listPerson:24, PersonService (com.paincupid.springmvc.service)
    listPerson:35, PersonController (com.paincupid.springmvc.controller)

从`controller`一路调用下去。`PersonController`调用 `PersonService`。

1、`PersonService`调用 `PersonMapper`的时候，会调用它的代理类 `MapperProxy`。

2、`MapperProxy`执行由`MapperMethod`执行：`mapperMethod.execute(sqlSession, args);`

##  ##

## 3.3 MapperProxy 代理Mapper执行 ##

MapperProxy 代理实例生成，在调用后加了一层缓存。

public class MapperProxy<T> implements InvocationHandler, Serializable { 
    
      private static final long serialVersionUID = -6424540398559729838L;
      private final SqlSession sqlSession;
      private final Class<T> mapperInterface;
      private final Map<Method, MapperMethod> methodCache;
    
      public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) { 
        this.sqlSession = sqlSession;
        this.mapperInterface = mapperInterface;
        this.methodCache = methodCache;
      }
    
      @Override
      public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { 
        try { 
          if (Object.class.equals(method.getDeclaringClass())) { 
            return method.invoke(this, args);
          } else if (isDefaultMethod(method)) { 
            return invokeDefaultMethod(proxy, method, args);
          }
        } catch (Throwable t) { 
          throw ExceptionUtil.unwrapThrowable(t);
        }
        final MapperMethod mapperMethod = cachedMapperMethod(method);//将新生成的MapperMethod缓存起来
        return mapperMethod.execute(sqlSession, args);
      }    
      //...
    }

MapperMethod持有 `mapperInterface`、`method`、`Configuration`

private MapperMethod cachedMapperMethod(Method method) { 
      MapperMethod mapperMethod = methodCache.get(method);
      if (mapperMethod == null) { 
        mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
        methodCache.put(method, mapperMethod);
      }
      return mapperMethod;
    }

## 3.4 MapperMethod\#execute ##

### 3.4.1 MapperMethod\#execute ###

MapperMethod会调用

public Object execute(SqlSession sqlSession, Object[] args) { 
      Object result;
      switch (command.getType()) { 
        case INSERT: { 
       Object param = method.convertArgsToSqlCommandParam(args);
          result = rowCountResult(sqlSession.insert(command.getName(), param));
          break;
        }
        case UPDATE: { 
          Object param = method.convertArgsToSqlCommandParam(args);
          result = rowCountResult(sqlSession.update(command.getName(), param));
          break;
        }
        case DELETE: { 
          Object param = method.convertArgsToSqlCommandParam(args);
          result = rowCountResult(sqlSession.delete(command.getName(), param));
          break;
        }
        case SELECT:
          if (method.returnsVoid() && method.hasResultHandler()) { 
            executeWithResultHandler(sqlSession, args);
            result = null;
          } else if (method.returnsMany()) { 
            result = executeForMany(sqlSession, args);//<---------
          } else if (method.returnsMap()) { 
            result = executeForMap(sqlSession, args);
          } else if (method.returnsCursor()) { 
            result = executeForCursor(sqlSession, args);
          } else { 
            Object param = method.convertArgsToSqlCommandParam(args);
            result = sqlSession.selectOne(command.getName(), param);
          }
          break;
        case FLUSH:
          result = sqlSession.flushStatements();
          break;
        default:
          throw new BindingException("Unknown execution method for: " + command.getName());
      }
      if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) { 
        throw new BindingException("Mapper method '" + command.getName() 
            + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
      }
      return result;
    }

### 3.4.2 executeForMany ###

private <E> Object executeForMany(SqlSession sqlSession, Object[] args) { 
      List<E> result;
      Object param = method.convertArgsToSqlCommandParam(args);
      if (method.hasRowBounds()) { 
        RowBounds rowBounds = method.extractRowBounds(args);
        //sqlSession是SqlSessionTemplate <----------
        result = sqlSession.<E>selectList(command.getName(), param, rowBounds);
      } else { 
        result = sqlSession.<E>selectList(command.getName(), param);
      }
      // issue #510 Collections & arrays support
      if (!method.getReturnType().isAssignableFrom(result.getClass())) { 
        if (method.getReturnType().isArray()) { 
          return convertToArray(result);
        } else { 
          return convertToDeclaredCollection(sqlSession.getConfiguration(), result);
        }
      }
      return result;
    }

可以看到还是由`sqlSession` 执行，此处`sqlSession` ，就是上面的`SqlSessionTemplate`，所以会执行`SqlSessionTemplate.selectList()`

## 3.5 SqlSessionTemplate\#selectList ##

@Override
    public <E> List<E> selectList(String statement, Object parameter) { 
      return this.sqlSessionProxy.<E> selectList(statement, parameter);
    }

调用`sqlSessionProxy`时，会被`SqlSessionInterceptor`拦截。反射执行其方法。

## 3.5 SqlSessionInterceptor\#invoke ##

执行`sqlSession.<E>selectList`（`SqlSessionTemplate.selectList`）的时候 ，会被拦截器`SqlSessionIntercepteor`拦截，上面已经讲过。然后先getSession方法，得到的是 `DefaultSqlSession`。

![SqlSessionInterceptor.png][]

private class SqlSessionInterceptor implements InvocationHandler { 
      @Override
      public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { 
        SqlSession sqlSession = getSqlSession(
            SqlSessionTemplate.this.sqlSessionFactory,
            SqlSessionTemplate.this.executorType,
            SqlSessionTemplate.this.exceptionTranslator);
        try { 
          Object result = method.invoke(sqlSession, args);
          if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) { 
            // force commit even on non-dirty sessions because some databases require
            // a commit/rollback before calling close()
            sqlSession.commit(true);
          }
          return result;
        } //...
      }
    }

在`getSqlSession()`上面介绍过了这一步，创建了DefaultSqlSession、事务、执行器。事务保存在执行器中， DefaultSqlSession持有执行器、configuration

`method.invoke`代理的是`DefaultSqlSession`

## 3.7 DefaultSqlSession\#selectList ##

DefaultSqlSession\#selectList

先取出MappedStatement，然后执行查询，调用`executor.query`，之前的准备工作分析了，`DefaultSqlSession`持有执行器`Executor`

@Override
    public <E> List<E> selectList(String statement, Object parameter) { 
      return this.selectList(statement, parameter, RowBounds.DEFAULT);
    }
    
    @Override
    public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) { 
      try { 
        MappedStatement ms = configuration.getMappedStatement(statement);
        return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
      } //....
    }

## 3.8 CachingExecutor\#query ##

CachingExecutor\#query

@Override
    public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException { 
      BoundSql boundSql = ms.getBoundSql(parameterObject);
      CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
      return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
    }

CachingExecutor\#query

@Override
    public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
        throws SQLException { 
      Cache cache = ms.getCache();
      if (cache != null) { 
        flushCacheIfRequired(ms);
        if (ms.isUseCache() && resultHandler == null) { 
          ensureNoOutParams(ms, parameterObject, boundSql);
          @SuppressWarnings("unchecked")
          List<E> list = (List<E>) tcm.getObject(cache, key);
          if (list == null) { 
            list = delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
            tcm.putObject(cache, key, list); // issue #578 and #116
          }
          return list;
        }
      }
      return delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
    }

delegate代理的是自己，此处的delegate是`SimpleExecutor`

public class CachingExecutor implements Executor { 
    
      private Executor delegate;
      private TransactionalCacheManager tcm = new TransactionalCacheManager();
    
      public CachingExecutor(Executor delegate) { 
        this.delegate = delegate;
        delegate.setExecutorWrapper(this); //代理的是自己
      }
    }

## 3.9 SimpleExecutor ##

### 3.9.1 BaseExecutor\#query ###

SimpleExecutor执行继承自父类方法：BaseExecutor\#query

@Override
    public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { 
      ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());
      if (closed) { 
        throw new ExecutorException("Executor was closed.");
      }
      if (queryStack == 0 && ms.isFlushCacheRequired()) { 
        clearLocalCache();
      }
      List<E> list;
      try { 
        queryStack++;
        //localCache是个PerpetualCache类型的实例，PerpetualCache类是实现了MyBatis的Cache缓存接口的实现类之一，内部有个Map<Object, Object>类型的属性用来存储缓存数据。 这个localCache就是一级缓存！ 
        list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
        if (list != null) { 
          handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
        } else { 
          // <------------ 
          list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
        }
      } finally { 
        queryStack--;
      }
      if (queryStack == 0) { 
        for (DeferredLoad deferredLoad : deferredLoads) { 
          deferredLoad.load();
        }
        // issue #601
        deferredLoads.clear();
        if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) { 
          // issue #482
          clearLocalCache();
        }
      }
      return list;
    }

localCache是个PerpetualCache类型的实例，PerpetualCache类是实现了MyBatis的Cache缓存接口的实现类之一，内部有个Map<Object, Object>类型的属性用来存储缓存数据。 这个localCache就是一级缓存！

### 3.9.2 BaseExecutor\#queryFromDatabase ###

SimpleExecutor执行继承自父类方法：BaseExecutor\#queryFromDatabase

private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { 
      List<E> list;
      localCache.putObject(key, EXECUTION_PLACEHOLDER);
      try { 
        list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
      } finally { 
        localCache.removeObject(key);
      }
      localCache.putObject(key, list);
      if (ms.getStatementType() == StatementType.CALLABLE) { 
        localOutputParameterCache.putObject(key, parameter);
      }
      return list;
    }

### 3.9.3 SimpleExecutor\#doQuery ###

SimpleExecutor创建StatementHandler，由StatementHandler以

@Override
    public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException { 
      Statement stmt = null;
      try { 
        Configuration configuration = ms.getConfiguration();
        StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
        stmt = prepareStatement(handler, ms.getStatementLog());// <----------
        return handler.<E>query(stmt, resultHandler);// <----------
      } finally { 
        closeStatement(stmt);
      }
    }

### 3.9.4 SimpleExecutor\#prepareStatement ###

像jdbc一样，先建立`Connection`，然后再建`Statement`。

把`Statement`委托给`StatementHandler`最后去执行。

private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException { 
      Statement stmt;
      Connection connection = getConnection(statementLog);
      stmt = handler.prepare(connection, transaction.getTimeout());
      handler.parameterize(stmt);
      return stmt;
    }

## 3.10 RoutingStatementHandler\#query ##

public class RoutingStatementHandler implements StatementHandler { 
      private final StatementHandler delegate;
    
      @Override
      public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException { 
        return delegate.<E>query(statement, resultHandler);
    }

此处`delegate`的值是：`PreparedStatementHandler`

## 3.11 PreparedStatementHandler\#query ##

最后由`PreparedStatement`执行查询操作，由`ResultHandler`处理返回结果集。

@Override
    public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException { 
      PreparedStatement ps = (PreparedStatement) statement;
      ps.execute();
      return resultSetHandler.<E> handleResultSets(ps);
    }

这就是一个查询的整个调用过程了。

# 四、MyBatis核心构件 #

<table> 
 <thead> 
  <tr> 
   <th>名称</th> 
   <th>作用</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>SqlSession</td> 
   <td>作为MyBatis工作的主要顶层API，表示和数据库交互的会话，完成必要数据库增删改查功能</td> 
  </tr> 
  <tr> 
   <td>Executor</td> 
   <td>MyBatis执行器，是MyBatis 调度的核心，负责SQL语句的生成和查询缓存的维护</td> 
  </tr> 
  <tr> 
   <td>StatementHandler</td> 
   <td>封装了JDBC Statement操作，负责对JDBC statement 的操作，如设置参数、将Statement结果集转换成List集合</td> 
  </tr> 
  <tr> 
   <td>ParameterHandler</td> 
   <td>负责对用户传递的参数转换成JDBC Statement 所需要的参数</td> 
  </tr> 
  <tr> 
   <td>ResultSetHandler</td> 
   <td>负责将JDBC返回的ResultSet结果集对象转换成List类型的集合</td> 
  </tr> 
  <tr> 
   <td>TypeHandler</td> 
   <td>负责java数据类型和jdbc数据类型之间的映射和转换</td> 
  </tr> 
  <tr> 
   <td>MappedStatement</td> 
   <td>MappedStatement维护了一条select</td> 
  </tr> 
  <tr> 
   <td>SqlSource</td> 
   <td>负责根据用户传递的parameterObject，动态地生成SQL语句，将信息封装到BoundSql对象中，并返回</td> 
  </tr> 
  <tr> 
   <td>BoundSql</td> 
   <td>表示动态生成的SQL语句以及相应的参数信息</td> 
  </tr> 
  <tr> 
   <td>Configuration</td> 
   <td>MyBatis所有的配置信息都维持在Configuration对象之中</td> 
  </tr> 
 </tbody> 
</table>

# 五、事务 #

--------------------

MyBatis自动参与到spring事务管理中，无需额外配置，只要org.mybatis.spring.SqlSessionFactoryBean引用的数据源与DataSourceTransactionManager引用的数据源一致即可，否则事务管理会不起作用。

另外需要下载依赖包[aopalliance][].jar放置到WEB-INF/lib目录下。否则spring初始化时会报异常  
java.lang.NoClassDefFoundError: org/aopalliance/intercept/MethodInterceptor

## 5.1 mybatis-spring的Transaction准备阶段 ##

下面一段是复制别人的博客，感觉有道理，就直接拿来用了。

> 下面方法中有一个步骤是如果用户没有配置`transactionFactory`，默认将Mybatis的`transactionFactory`配置为`SpringManagedTransactionFactory`，我们在分析Mybatis源码的时候看到，在用户没有指定`transactionFactory`配置的时候，Mybatis使用`ManagedTransactionFactory`作为默认的`TransactionFactory`，Mybatis在创建`SqlSession`时，需要为其添加一个Executor执行器，构建`Executor`执行器时需要的Transaction对象就是通过`TransactionFactory`的`newTransaction`方法创建的，后续`Executor`执行sql命令时会通过`Transaction`的`getConnection`方法获取数据库连接，这里添加的`SpringManagedTransactionFactory`有什么作用呢？我们可以思考一下，Spring在开启事务的时候需要获取数据库连接，Mybatis执行的时候也要获取数据库连接，在一次调用过程中，两者配合使用时，如果想让Spring的事务作用于Mybatis的数据库操作，那么在这次调用的过程中两者肯定要共用同一个数据库连接，不然事务无法生效，`SpringManagedTransactionFactory`就可以解决共用数据库连接的问题。

1.2.4介绍了`buildSqlSessionFactory()`方法，返回了`DefaultSqlSessionFactory`。

SqlSessionFactoryBean\#buildSqlSessionFactory 在创建`DefaultSqlSessionFactory`时，创建了`SpringManagedTransactionFactory`，并将它放到`configuration`中。

protected SqlSessionFactory buildSqlSessionFactory() throws IOException { 
    
      Configuration configuration;
      //....
      if (this.transactionFactory == null) { 
        this.transactionFactory = new SpringManagedTransactionFactory();//<--
      }
      		
      configuration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource));  
    
      return this.sqlSessionFactoryBuilder.build(configuration);
    }

调用如下图所示：

![SpringManagedTransactionFactory.png][]

`SpringManagedTransactionFactory`继承了mybatis的`TransactionFactory`

## 5.2 mybatis-spring创建SqlSession，并交由spring去得到connection ##

SqlSession的调用栈如下：

getConnection:150, ConnectionHolder (org.springframework.jdbc.datasource)
    doGetConnection:106, DataSourceUtils (org.springframework.jdbc.datasource)
    getConnection:77, DataSourceUtils (org.springframework.jdbc.datasource)
    openConnection:82, SpringManagedTransaction (org.mybatis.spring.transaction)
    getConnection:68, SpringManagedTransaction (org.mybatis.spring.transaction)
    getConnection:336, BaseExecutor (org.apache.ibatis.executor)
    prepareStatement:84, SimpleExecutor (org.apache.ibatis.executor)
    doUpdate:49, SimpleExecutor (org.apache.ibatis.executor)
    update:117, BaseExecutor (org.apache.ibatis.executor)
    update:76, CachingExecutor (org.apache.ibatis.executor)
    update:198, DefaultSqlSession (org.apache.ibatis.session.defaults)
    insert:185, DefaultSqlSession (org.apache.ibatis.session.defaults)
    invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
    invoke:62, NativeMethodAccessorImpl (sun.reflect)
    invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
    invoke:497, Method (java.lang.reflect)
    invoke:433, SqlSessionTemplate$SqlSessionInterceptor (org.mybatis.spring)
    insert:-1, $Proxy13 (com.sun.proxy)
    insert:278, SqlSessionTemplate (org.mybatis.spring)
    execute:57, MapperMethod (org.apache.ibatis.binding)
    invoke:59, MapperProxy (org.apache.ibatis.binding)
    insertStudentByVoMapper:-1, $Proxy25 (com.sun.proxy)
    testTransactional:35, StudentService (com.paincupid.springmvc.service)

调用入口已经讲过，SqlSessionInterceptor\#invoke阶段，SqlSessionUtils\#getSqlSession()方法，再来看一下：

`TransactionSynchronizationManager`已经是spring包下的类了`org.springframework.transaction.support.getResource`，根据当前的`sessionFactory`做key，拿到当前的`SqlSessionHolder`。`org.mybatis.spring.SqlSessionUtils`是mybatis-spring包下的类，这个类比较重要，尤其是`getSqlSession`方法，是spring和mybatis的结合点。

SqlSessionUtils\#getSqlSession

public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) { 
    
      notNull(sessionFactory, NO_SQL_SESSION_FACTORY_SPECIFIED);
      notNull(executorType, NO_EXECUTOR_TYPE_SPECIFIED);
    
      SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);
    
      SqlSession session = sessionHolder(executorType, holder);
      if (session != null) { 
        return session;
      }
    
      session = sessionFactory.openSession(executorType); //new DefaultSqlSession <-----
    
      registerSessionHolder(sessionFactory, executorType, exceptionTranslator, session);
    
      return session;
    }

> session = sessionFactory.openSession(executorType);

### 5.2.2 openSession 时创建mybatis事务 ###

本质就是将**当前的`dataSource`放入`SpringManagedTransaction`对象中**。

2.3 DefaultSqlSessionFactory\#openSession时，会创建事务，前面已介绍过。

DefaultSqlSessionFactory\#openSessionFromConnection

> final Transaction tx = transactionFactory.newTransaction(connection);

相当于调用`SpringManagedTransactionFactory.newTransaction`，此处创建的是mybatis事务，`SpringManagedTransaction`负责mybatis的提交、回滚等。

`SpringManagedTransaction`后由spring调用：`SpringManagedTransaction.commit()`(如果事务交由 spring去控制，那么不会真正提交，最后还是调用spring的方法去提交事务。)

**为什么spring能调用到`SpringManagedTransaction`呢？ 是因为通过将它注册到spring的事务同步管理器：`TransactionSynchronizationManager`中，这样就完成了spring对mybatis的事务管理。**

public Transaction newTransaction(DataSource dataSource, TransactionIsolationLevel level, boolean autoCommit) { 
      return new SpringManagedTransaction(dataSource);
    }
    public SpringManagedTransaction(DataSource dataSource) { 
      notNull(dataSource, "No DataSource specified");
      this.dataSource = dataSource;
    }

### 5.2.3 保存前当sqlSession，创建并注册事务同步器。 ###

SqlSessionUtils\#registerSessionHolder

创建`SqlSessionHolder`对象, 将当前的`session`, `executorType`, `exceptionTranslator`存进去。然后通过spring的`TransactionSynchronizationManager.bindResource`方法， sessionFactory做key，holder作value，存起来，下次进getSqlSession时从缓存中取出来直接用，如果能取出holder，并从holer中得到session，则直接返回。

**看到`TransactionSynchronizationManager.register*()`方法，那就是spring和mybatis的结合点，通过`mybatis-spring`将spring和mybatis结合起来了。**

private static void registerSessionHolder(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator, SqlSession session) { 
      SqlSessionHolder holder;
      if (TransactionSynchronizationManager.isSynchronizationActive()) { 
        Environment environment = sessionFactory.getConfiguration().getEnvironment();
    
        if (environment.getTransactionFactory() instanceof SpringManagedTransactionFactory) { 
          LOGGER.debug(() -> "Registering transaction synchronization for SqlSession [" + session + "]");
    
          holder = new SqlSessionHolder(session, executorType, exceptionTranslator);
            
          TransactionSynchronizationManager.bindResource(sessionFactory, holder);
          //事务的处理，后面介绍，这里和spring结合，调用spring的TransactionSynchronizationManager
          TransactionSynchronizationManager.registerSynchronization(new SqlSessionSynchronization(holder, sessionFactory));
          holder.setSynchronizedWithTransaction(true);
          holder.requested();
        }//...
      }

`TransactionSynchronizationManager.bindResource`绑定当前`sessionFactory`和`holder`

`TransactionSynchronizationManager.registerSynchronization`为当前线程注册一个事务同步器，其实就是创建一个`SqlSessionSynchronization`放到`ThreadLocal`中，交给spring去管理。后面执行完sql后，提交时，再由spring交由mybatis-spring从TransactionSynchronizationManager取出来，然后从holder中拿 到sqSession提交。

private static final ThreadLocal<Set<TransactionSynchronization>> synchronizations =
    			new NamedThreadLocal<>("Transaction synchronizations");
    /** * Register a new transaction synchronization for the current thread. * Typically called by resource management code. * <p>Note that synchronizations can implement the * {@link org.springframework.core.Ordered} interface. * They will be executed in an order according to their order value (if any). * @param synchronization the synchronization object to register * @throws IllegalStateException if transaction synchronization is not active * @see org.springframework.core.Ordered */
    public static void registerSynchronization(TransactionSynchronization synchronization)
          throws IllegalStateException { 
    
       Assert.notNull(synchronization, "TransactionSynchronization must not be null");
       if (!isSynchronizationActive()) { 
          throw new IllegalStateException("Transaction synchronization is not active");
       }
       synchronizations.get().add(synchronization);
    }

### 5.2.4 SpringManagedTransaction.getConnection()取出当前connection ###

3.9.4 SimpleExecutor\#prepareStatement时，调用getConnect()时，会从之前的`SpringManagedTransaction`得到当前的connection

protected Connection getConnection(Log statementLog) throws SQLException { 
      Connection connection = transaction.getConnection();
      if (statementLog.isDebugEnabled()) { 
        return ConnectionLogger.newInstance(connection, statementLog, queryStack);
      } else { 
        return connection;
      }
    }

SpringManagedTransaction\#getConnection

@Override
    public Connection getConnection() throws SQLException { 
      if (this.connection == null) { 
        openConnection();
      }
      return this.connection;
    }

#### SpringManagedTransaction\#openConnection ####

**此处是`mybatis-spring`用来结合spring的，mybatis的dataSource交由spring去管理和获取。也是通过`mybatis-spring.jar`包中的`SpringManagedTransaction`**

由spring去创建Connection，同时设置`this.isConnectionTransactional`为`true`，后面调用mybatis的commit方法时，就无法commit，交给spring提交commit。

private void openConnection() throws SQLException { 
      this.connection = DataSourceUtils.getConnection(this.dataSource);
      this.autoCommit = this.connection.getAutoCommit();
      this.isConnectionTransactional = DataSourceUtils.isConnectionTransactional(this.connection, this.dataSource);
    }

### 5.2.5 交由spring根据dataSource去创建Connection ###

DataSourceUtils\#getConnection

`org.springframework.jdbc.datasource.DataSourceUtils.getConnection()`

public static Connection getConnection(DataSource dataSource) throws CannotGetJdbcConnectionException { 
        try { 
            return doGetConnection(dataSource);
        } //...
    }

`org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection()` 如果从事务同步管理器的当前线程中取不到`dataSource`，则会从jdbc中得到`connection`，放到`ConnectionHolder`中。然后：为当前线程注册一个新的事务同步器 和 绑定当前dataSource和holder到事务同步器。

因为本项目用的是`druid`，所以在IOC启动的时候，`dataSource`中的`connection`已经是被`druid`代理的`connection`:`ConnectionProxyImpl`

DataSourceUtils\#doGetConnection

public static Connection doGetConnection(DataSource dataSource) throws SQLException { 
        Assert.notNull(dataSource, "No DataSource specified");
        // 从当前dataSource中获取绑定的ConnectionHolder
        ConnectionHolder conHolder = (ConnectionHolder)TransactionSynchronizationManager.getResource(dataSource);
        if (conHolder == null || !conHolder.hasConnection() && !conHolder.isSynchronizedWithTransaction()) { 
            logger.debug("Fetching JDBC Connection from DataSource");
            Connection con = fetchConnection(dataSource);
            //
            if (TransactionSynchronizationManager.isSynchronizationActive()) { 
                logger.debug("Registering transaction synchronization for JDBC Connection");
                // 在事务中使用相同的连接进一步JDBC操作，线程绑定对象将在事务完成时被同步删除
                ConnectionHolder holderToUse = conHolder;
                if (conHolder == null) { 
                    holderToUse = new ConnectionHolder(con);
                } else { 
                    conHolder.setConnection(con);
                }
                // 将ConnectionHolder请求数+1
                holderToUse.requested();           
                // 为当前线程注册一个新的事务同步器
                TransactionSynchronizationManager.registerSynchronization(new DataSourceUtils.ConnectionSynchronization(holderToUse, dataSource));
                holderToUse.setSynchronizedWithTransaction(true);
                if (holderToUse != conHolder) { 
                    //绑定当前dataSource和holder到事务同步器
                    TransactionSynchronizationManager.bindResource(dataSource, holderToUse);
                }
            }
    
            return con;
        } else { 
            conHolder.requested();
            if (!conHolder.hasConnection()) { 
                logger.debug("Fetching resumed JDBC Connection from DataSource");
                conHolder.setConnection(fetchConnection(dataSource));
            }
    
            return conHolder.getConnection();
        }
    }

这里我们看到通过调用TransactionSynchronizationManager的getResource方法获取当前线程绑定的ConnectionHolder，TransactionSynchronizationManager这个类我们在分析Spring事务源码的时候看到过，用来管理每个线程的资源和事务同步，内部维护了很多ThreadLocal变量来保存一些线程相关的资源。

方法中我们发现有一个注册事务同步的过程，这个事务同步是做什么用的呢？我们在分析Spring事务源码的时候提到过，在Spring事务回滚、提交、挂起等操作时会激活事务同步的相关方法，而这里添加的事务同步的作用主要是在Spring事务提交、回滚等操作后将ConnectionHolder的请求数量置为0、将一些属性置为初始状态、将数据库连接放回连接池、释放数据库连接等。

===================

## 5.3 spring事务调用 ##

如果是spring配置了事务，那么会在IOC的时候 ，在@Transactional的注解的Service上，加代理。在调用目标代理方法前，会先调用CGLIB代理：在调用到@Transactional 注解方法时，匹配上了CGLIB代理CglibAopProxy$DynamicAdvisedInterceptor\#intercept， 然后会先执行TransactionInterceptor\#invoke事务拦截器，通过TransactionAspectSupport\#invokeWithinTransaction来调用AbstractPlatformTransactionManager\#getTransaction，开始spring事务：getTransaction，在DataSourceTransactionManager\#doBegin时，创建链接Connection。

### 5.3.1 执行过程摘要 ###

#### **invokeWithinTransaction** ####

事务相关的部分，基本上是围绕着 `TransactionAspectSupport.invokeWithinTransaction`这个方法的，在service方法执行前，先执行`createTransactionIfNecessary`创建`TransactionStatus`并保存到当前线程中；第二步执行真正Mapper的sql方法；第三步，在返回前执行事务提交。其本质就是一个环切面。

TransactionAspectSupport\#invokeWithinTransaction

protected Object invokeWithinTransaction(Method method, Class<?> targetClass, final InvocationCallback invocation) throws Throwable { 
    
       // If the transaction attribute is null, the method is non-transactional.
       final TransactionAttribute txAttr = getTransactionAttributeSource().getTransactionAttribute(method, targetClass);
       //创建DataSourceTransactionManager，并为DataSourceTransactionManager赋值dataSoucre属性值 
       final PlatformTransactionManager tm = determineTransactionManager(txAttr);
       final String joinpointIdentification = methodIdentification(method, targetClass);
    
       if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) { 
          // Standard transaction demarcation with getTransaction and commit/rollback calls.
          // 在执行sql前创建事务，如果加了@Transactional后会走到这里 <----- sql执行前开户事务
          TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
          Object retVal = null;
          try { 
             // This is an around advice: Invoke the next interceptor in the chain.
             // This will normally result in a target object being invoked.
             retVal = invocation.proceedWithInvocation(); // <----执行真正mapper方法
          }
          catch (Throwable ex) { 
             // target invocation exception
             completeTransactionAfterThrowing(txInfo, ex);
             throw ex;
          }
          finally { 
             cleanupTransactionInfo(txInfo);
          }
          //在执行完service中的mapper sql语句后，会用TransactionStatus执行最后的提交。 
          //<----- sql执行后提交
          commitTransactionAfterReturning(txInfo);
          return retVal;
       }
        //.....
    }

### 5.3.2 执行目标方法(`Service.*methoad()`)前的CGLIB代理拦截器调用 ###

#### 创建`PlatformTransactionManager(DataSourceTransactionManager)`，并为`DataSourceTransactionManager`的属性`dataSoucre`赋值 ####

`DataSourceTransactionManager`继承了`AbstractPlatformTransactionManager`，创建的其实是`DataSourceTransactionManager`实例。

![DataSourceTransactionManager.png][]

以下栈信息就是创建`PlatformTransactionManager`:

> final PlatformTransactionManager tm = determineTransactionManager(txAttr);

setDataSource:146, DataSourceTransactionManager (org.springframework.jdbc.datasource)
    invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
    invoke:62, NativeMethodAccessorImpl (sun.reflect)
    invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
    invoke:497, Method (java.lang.reflect)
    setValue:344, BeanWrapperImpl$BeanPropertyHandler (org.springframework.beans)
    setPropertyValue:454, AbstractNestablePropertyAccessor (org.springframework.beans)
    setPropertyValue:280, AbstractNestablePropertyAccessor (org.springframework.beans)
    setPropertyValues:95, AbstractPropertyAccessor (org.springframework.beans)
    setPropertyValues:75, AbstractPropertyAccessor (org.springframework.beans)
    applyPropertyValues:1514, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    populateBean:1226, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    doCreateBean:543, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    createBean:482, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    getObject:305, AbstractBeanFactory$1 (org.springframework.beans.factory.support)
    getSingleton:230, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support)
    doGetBean:301, AbstractBeanFactory (org.springframework.beans.factory.support)
    getBean:201, AbstractBeanFactory (org.springframework.beans.factory.support)
    getBeansOfType:534, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    getBeansOfType:523, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    beansOfTypeIncludingAncestors:261, BeanFactoryUtils (org.springframework.beans.factory)
    qualifiedBeanOfType:80, BeanFactoryAnnotationUtils (org.springframework.beans.factory.annotation)
    qualifiedBeanOfType:56, BeanFactoryAnnotationUtils (org.springframework.beans.factory.annotation)
    determineQualifiedTransactionManager:378, TransactionAspectSupport (org.springframework.transaction.interceptor)
    determineTransactionManager:362, TransactionAspectSupport (org.springframework.transaction.interceptor)
    invokeWithinTransaction:271, TransactionAspectSupport (org.springframework.transaction.interceptor)
    invoke:96, TransactionInterceptor (org.springframework.transaction.interceptor)
    proceed:179, ReflectiveMethodInvocation (org.springframework.aop.framework)
    intercept:653, CglibAopProxy$DynamicAdvisedInterceptor (org.springframework.aop.framework)
    testTransactional:-1, StudentService$$EnhancerBySpringCGLIB$$4461afed (com.paincupid.springmvc.service)
    listTran:50, StudentController (com.paincupid.springmvc.controller)

`beanName`为`transactionManager`的类 `org.springframework.jdbc.datasource.DataSourceTransactionManager`是`singleton`的。因为`DataSourceTransactionManager`就单例，所以只有服务重启后，`dataSrouce`只会被set一次，以后取单例，只会在缓存中取。

#### CGLIB代理拦截器栈调用过程 ####

doBegin:204, DataSourceTransactionManager (org.springframework.jdbc.datasource)
    getTransaction:373, AbstractPlatformTransactionManager (org.springframework.transaction.support)
    createTransactionIfNecessary:427, TransactionAspectSupport (org.springframework.transaction.interceptor)
    invokeWithinTransaction:276, TransactionAspectSupport (org.springframework.transaction.interceptor)
    invoke:96, TransactionInterceptor (org.springframework.transaction.interceptor)
    proceed:179, ReflectiveMethodInvocation (org.springframework.aop.framework)
    intercept:653, CglibAopProxy$DynamicAdvisedInterceptor (org.springframework.aop.framework)
    testTransactional:-1, StudentService$$EnhancerBySpringCGLIB$$2e9a2dc4 (com.paincupid.springmvc.service)
    listTran:28, StudentController (com.paincupid.springmvc.controller)

###  ###

\*\*摘要过程：AbstractPlatformTransactionManager\#getTransaction创建TransactionStatus，返回后绑定到当前线程。 \*\*

DataSourceTransactionManager\#doBegin作用

1、 创建Connection 并放到ConnectionHolder中保存起来。

> Connection newCon = this.dataSource.getConnection();
> 
> txObject.setConnectionHolder(new ConnectionHolder(newCon), true);

2、除了创建connectionHolder，它还会设置并保存上一个事务的隔离级别：isolation level。

> Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);txObject.setPreviousIsolationLevel(previousIsolationLevel);

3、最后将dataSrouce和connection绑定到`TransactionSynchronizationManager`中

> TransactionSynchronizationManager.bindResource(getDataSource(), txObject.getConnectionHolder());

在`getTransaction()`方法最主要是功能还是创建`TransactionStatus`(`DefaultTransactionStatus`)，并返回。

在`TransactionAspectSupport.createTransactionIfNecessary`得到`TransactionStatus`后，将它包装成`TransactionInfo`

并把它绑定到当前线程。

TransactionAspectSupport\#prepareTransactionInfo

> txInfo.bindToThread();

TransactionAspectSupport$TransactionInfo\#bindToThread 主要是通过ThreadLocal保存`TransactionStatus`

private static final ThreadLocal<TransactionInfo> transactionInfoHolder =
    			new NamedThreadLocal<TransactionInfo>("Current aspect-driven transaction");
    private void bindToThread() { 
       // Expose current TransactionStatus, preserving any existing TransactionStatus
       // for restoration after this transaction is complete.
       this.oldTransactionInfo = transactionInfoHolder.get();
       transactionInfoHolder.set(this);
    }

执行完代理，会执行真正的service方法：StudentService\#testTransactional

### 5.3.3 执行目标方法(`Service.*methoad()`) ###

执行方法栈如下图所示。同时可以看到`studentVoMapper`的执行其它是交给`org.apache.ibatis.binding.MapperProxy@7fecf7ab`去执行的。上面已经讲解了`MapperProxy`的调用过程 。

![mybatis-trans-invoke1.png][]

后执行\*mapper.insert方法

### 5.3.4 执行目标方法(`Service.*methoad()`)后的CGLIB代理拦截器调用：commit提交 ###

#### commit真正提交栈信息打印 ####

commit:750, DruidPooledConnection (com.alibaba.druid.pool)
    doCommit:272, DataSourceTransactionManager (org.springframework.jdbc.datasource)
    processCommit:761, AbstractPlatformTransactionManager (org.springframework.transaction.support)
    commit:730, AbstractPlatformTransactionManager (org.springframework.transaction.support)
    commitTransactionAfterReturning:485, TransactionAspectSupport (org.springframework.transaction.interceptor)
    invokeWithinTransaction:291, TransactionAspectSupport (org.springframework.transaction.interceptor)
    invoke:96, TransactionInterceptor (org.springframework.transaction.interceptor)
    proceed:179, ReflectiveMethodInvocation (org.springframework.aop.framework)
    intercept:653, CglibAopProxy$DynamicAdvisedInterceptor (org.springframework.aop.framework)
    testTransactional:-1, StudentService$$EnhancerBySpringCGLIB$$4461afed (com.paincupid.springmvc.service)
    listTran:50, StudentController (com.paincupid.springmvc.controller)

/在执行完service中的mapper sql语句后，会用TransactionStatus执行最后的提交。在doBegin的时候，先将自动提交设置成了false.

DataSourceTransactionManager\#doBegin 自动提交设置在false，所以在执行真正的service目标方法时不会提交到数据库。

if (con.getAutoCommit()) { 
       txObject.setMustRestoreAutoCommit(true);
       if (logger.isDebugEnabled()) { 
          logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
       }
       con.setAutoCommit(false);
    }

#### DataSourceTransactionManager\#doCommit 真正提交 ####

@Override
    protected void doCommit(DefaultTransactionStatus status) { 
       DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
       Connection con = txObject.getConnectionHolder().getConnection();
       if (status.isDebug()) { 
          logger.debug("Committing JDBC transaction on Connection [" + con + "]");
       }
       try { 
          con.commit();
       }
       catch (SQLException ex) { 
          throw new TransactionSystemException("Could not commit JDBC transaction", ex);
       }
    }

因为项目用的是druid，所以，connection的值为：

> com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@28d21ddc

由druid做了connection的代理。

#### 真正提交前的预提交 ####

在真正提交前，会执行预提交。

commit:107, SpringManagedTransaction (org.mybatis.spring.transaction)
    commit:244, BaseExecutor (org.apache.ibatis.executor)
    commit:119, CachingExecutor (org.apache.ibatis.executor)
    commit:224, DefaultSqlSession (org.apache.ibatis.session.defaults)
    commit:218, DefaultSqlSession (org.apache.ibatis.session.defaults)
    beforeCommit:286, SqlSessionUtils$SqlSessionSynchronization (org.mybatis.spring)
    triggerBeforeCommit:95, TransactionSynchronizationUtils (org.springframework.transaction.support)
    triggerBeforeCommit:932, AbstractPlatformTransactionManager (org.springframework.transaction.support)
    processCommit:744, AbstractPlatformTransactionManager (org.springframework.transaction.support)
    commit:730, AbstractPlatformTransactionManager (org.springframework.transaction.support)
    commitTransactionAfterReturning:485, TransactionAspectSupport (org.springframework.transaction.interceptor)
    invokeWithinTransaction:291, TransactionAspectSupport (org.springframework.transaction.interceptor)
    invoke:96, TransactionInterceptor (org.springframework.transaction.interceptor)
    proceed:179, ReflectiveMethodInvocation (org.springframework.aop.framework)
    intercept:653, CglibAopProxy$DynamicAdvisedInterceptor (org.springframework.aop.framework)
    testTransactional:-1, StudentService$$EnhancerBySpringCGLIB$$4461afed (com.paincupid.springmvc.service)
    listTran:50, StudentController (com.paincupid.springmvc.controller)

AbstractPlatformTransactionManager\#processCommit

/** * Process an actual commit. * Rollback-only flags have already been checked and applied. * @param status object representing the transaction * @throws TransactionException in case of commit failure */
    private void processCommit(DefaultTransactionStatus status) throws TransactionException { 
       try { 
          boolean beforeCompletionInvoked = false;
          try { 
             prepareForCommit(status);
             triggerBeforeCommit(status); //执行mybatis提交 <-------
             triggerBeforeCompletion(status); //将sessionFactory和connectionHolder从当前线程解绑
             beforeCompletionInvoked = true;
             boolean globalRollbackOnly = false;
             if (status.isNewTransaction() || isFailEarlyOnGlobalRollbackOnly()) { 
                globalRollbackOnly = status.isGlobalRollbackOnly();
             }
             if (status.hasSavepoint()) { 
                //...
                status.releaseHeldSavepoint();
             }
             else if (status.isNewTransaction()) { 
                //...
                doCommit(status); //由spring提交 <-------
             }//....
          }//.....
    
          // Trigger afterCommit callbacks, with an exception thrown there
          // propagated to callers but the transaction still considered as committed.
          try { 
             triggerAfterCommit(status);
          }
          finally { 
             triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);
          }
       }
       finally { 
          cleanupAfterCompletion(status);
       }
    }

在执行`doCommit(status)`前，会先执行mybatis的commit: `triggerBeforeCommit`。会先从当前线程中取出线程同步器`TransactionSynchronizationManager.getSynchronizations()`。

##### TransactionSynchronizationUtils\#triggerBeforeCommit #####

/** * Trigger {@code beforeCommit} callbacks on all currently registered synchronizations. * @param readOnly whether the transaction is defined as read-only transaction * @throws RuntimeException if thrown by a {@code beforeCommit} callback * @see TransactionSynchronization#beforeCommit(boolean) */
    public static void triggerBeforeCommit(boolean readOnly) { 
       for (TransactionSynchronization synchronization : TransactionSynchronizationManager.getSynchronizations()) { 
          synchronization.beforeCommit(readOnly);
       }
    }

此处`synchronization`就是之前注册过的： `SqlSessionSynchronization$SqlSessionSynchronization`

在SqlSessionUtils\#registerSessionHolder方法中注册的。

> TransactionSynchronizationManager.registerSynchronization(new SqlSessionSynchronization(holder, sessionFactory));

SqlSessionSynchronization$SqlSessionSynchronization\#beforeCommit

@Override
    public void beforeCommit(boolean readOnly) { 
      // Connection commit or rollback will be handled by ConnectionSynchronization or
      // DataSourceTransactionManager.
      // But, do cleanup the SqlSession / Executor, including flushing BATCH statements so
      // they are actually executed.
      // SpringManagedTransaction will no-op the commit over the jdbc connection
      // TODO This updates 2nd level caches but the tx may be rolledback later on! 
      if (TransactionSynchronizationManager.isActualTransactionActive()) { 
        try { 
          this.holder.getSqlSession().commit(); //<---------
        } //....
      }
    }

`holder`值是`SqlSessionHolder`

> holder = new SqlSessionHolder(session, executorType, exceptionTranslator);

`this.holder.getSqlSession()`的值为`DefaultSqlSession`

SqlSessionUtils\#getSqlSession

> session = sessionFactory.openSession(executorType); //new DefaultSqlSession

DefaultSqlSession.commit --> CachingExecutor.commit --> BaseExecutor.commit --> SpringManagedTransaction.commit

SpringManagedTransaction\#commit

@Override
    public void commit() throws SQLException { 
      if (this.connection != null && !this.isConnectionTransactional && !this.autoCommit) { 
        if (LOGGER.isDebugEnabled()) { 
          LOGGER.debug("Committing JDBC Connection [" + this.connection + "]");
        }
        this.connection.commit();
      }
    }

由于 `this.isConnectionTransactional`值为`true`，所以不会执行`this.connection.commit();`，最后交由了spring去提交。

那么 `isConnectionTransactional`什么时候为 `ture` 的呢？

SpringManagedTransaction\#openConnection()

> this.isConnectionTransactional = DataSourceUtils.isConnectionTransactional(this.connection, this.dataSource);

DataSourceUtils\#isConnectionTransactional

public static boolean isConnectionTransactional(Connection con, DataSource dataSource) { 
       if (dataSource == null) { 
          return false;
       }
       ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
       return (conHolder != null && connectionEquals(conHolder, con));
    }

因为之前绑定了dataSource，所以此处ConnectionHolder不为空。connectionEquals为true.

##### TransactionSynchronizationUtils\#triggerBeforeCompletion #####

> TransactionSynchronizationManager.unbindResource(sessionFactory);

将sessionFactory和connectionHolder从当前线程解绑

# 六 spring事务调用总结 #

--------------------

## 6.1 调用 ##

当前端发起一次请求的时候，调用到目标方法 `*Service.*method()`方法时，如果加了@Transactional注解，springIOC的启动时，会对当前Service生成代理类，当匹配到@Transactional注解方法时，在执行前和执行后，会执行一些代理方法。事务的执行可以说是围绕着`TransactionAspectSupport.invokeWithinTransaction`来执行的。

**执行前：**

1.  创建DataSourceTransactionManager，并为DataSourceTransactionManager赋值dataSoucre属性值
    
    > final PlatformTransactionManager tm = determineTransactionManager(txAttr);
2.  前创建事务
    
    > TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
3.  在创建事务过程中，将`dataSource`和`connectionHolder`注册到事务同步器中，以便为mybatis获取执行，统一dataSource。
    
    > TransactionSynchronizationManager.bindResource(obtainDataSource(), txObject.getConnectionHolder());

**执行真正的目标方法**

可以参考第三章分析的\*Mapper调用过程。

这里主要把提交过程中和spring相关的部分提出来。尤其是SqlSessionUtils\#getSqlSession方法

1.  在执行\*Mapper的过程中，调用SqlSessionUtils\#getSqlSession方法，却获取当前的SqlSession，在执行getSqlSession()方法的过程中：
    
    A、先偿试从根据key:sessionFactory从TransactionSynchronizationManager中取SqlSessionHolder，获取到的话，直接从SqlSessionHolder中得到SqlSession返回。
    
    B、如果得不到，会通过`sessionFactory.openSession`创建SqlSession。在创建过程中，会由`SpringManagedTransaction.openConnection`会调用spring的类（`DataSourceUtils.getConnection`）去取connection，从而保证事务是同一个`Connection`。`DataSourceUtils.doGetConnection`会先根据`dataSource`为key，从
    
    > `ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource)`
    
    中去取，因为上面已经放进去了，所以从当前线程中就取到了ConnectionHolder，然后返回`Connection`：
    
    > `conHolder.getConnection()`

**执行后**

主要是执行`commitTransactionAfterReturning(txInfo);`方法

1.  `TransactionSynchronizationUtils.triggerBeforeCommit`预提交。因为之前注册过SqlSessionSynchronization：
    
    > `TransactionSynchronizationManager.registerSynchronization(new SqlSessionSynchronization(holder, sessionFactory));`
    
    所以预提交的时候，从TransactionSynchronizationManager取出`SqlSessionSynchronization`，然后得到SqlSessionHolder，后执行提交
    
    > this.holder.getSqlSession().commit();
    
    由于不满足条件，未能真正提交。
2.  通过\`\`TransactionSynchronizationUtils.triggerBeforeCompletion()`将`sessionFactory`和`connectionHolder\`从当前线程解绑
    
    > TransactionSynchronizationManager.unbindResource(sessionFactory);
3.  通过`DataSourceTransactionManager.doCommit()`真正执行：
    
    > Connection con = txObject.getConnectionHolder().getConnection();
    > 
    > con.commit();

不同的线程是怎么得到不同的connection?怎么做到同一个事务获取的是同一个connection?

从上面的getSqlSession()过程，每一次请求都会进行一次openSession，去spring中取一次connection，而这个connection可能是交由druid管理，从线程池中取出。

每次请求都会用同一个connection。虽然SessionFactory只会初始化一次，但每次请求前都会将sessionFactory和sessionHolder放到`TransactionSynchronizationManager`绑定到当前线程，即使一次请求如果有多个Mapper去执行，但放到同一个事物中，那么只会用同一个connection，因为下次还是从当线线程去取。当当线线程执行完所有的操作时，会将当前线程解绑sessionFactory。`TransactionSynchronizationManager`其实维护的是一个`ThreadLocal`。那么当下次请求或其它线程再进来时，因为正在执行的线程没有绑定过`TransactionSynchronizationManager`，所以取不到connectionHolder，这时又会回到线程池中去取connection。

结合 `ThreadLocal`实现了多么强大的功能！

# 七、 插一段初始化执行顺序 #

--------------------

doCreateBean创建Bean以及Bean的初始化顺序

AbtractAutowireCapableBeanFactory\#doCreateBean

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) { 
       // Instantiate the bean.
       BeanWrapper instanceWrapper = null;
       if (mbd.isSingleton()) { 
          instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
       }
       if (instanceWrapper == null) { 
          instanceWrapper = createBeanInstance(beanName, mbd, args);//<------1.4.1 实例化
       }
       //.....
    
       // Initialize the bean instance.
       Object exposedObject = bean;
       try { 
          populateBean(beanName, mbd, instanceWrapper); // <--------- 1.4.2 初始化
          if (exposedObject != null) { 
             exposedObject = initializeBean(beanName, exposedObject, mbd);
          }
       }
       //....
       return exposedObject;
    }

在执行完《1.4.1 实例化》后，会马上执行《1.4.2初始化》吗？

就Mapper的实例化来说，不是的。再通过MapperFactoryBean构造对象创建 MapperFactoryBean（Class mapperInterfacer的属性值为：interface com.paincupid.springmvc.persistence.PersonMapper）后，会行检查它的依赖。发现是SqlSessionFactory，然后再找谁还依赖了SqlSessionFactory，这时候会找到其它的MapperFactoryBean，然后通过反射构造函数将他们new出来，这时候反射时的入参就是其它mapper，比如：interface com.paincupid.springmvc.persistence.StudentMapper，将它放到缓存中。这些都做完后才会执行《1.4.2初始化操作》

\*Mapper注入过程，是由service来决定的，当service中有mapper属性性，容器会自动查找符合条件的mapper，找到后进行实例注入。

具体执行步骤：

1、执行行AbstractAutowireCapableBeanFactory\#populateBean时，如果RootBeanDefinition的类型是AUTOWIRE\_BY\_TYPE，那么会执行AbstractAutowireCapableBeanFactory\#autowireByType

2、AbstractAutowireCapableBeanFactory\#autowireByType 通过resolveDependency 得到sqlSessionFactory实例，并将它保存起来。然后，保存当前beanName和实例的关系: personMapper和sqlSessionFactory。

MutablePropertyValues pvs //是autowireByType的入参
    pvs.add(propertyName, autowiredArgument); //autowiredArgument就是sqlSessionFactory实例

3、DefaultListableBeanFactory\#resolveDependency --> DefaultListableBeanFactory\#doResolveDependency 返回依赖的对象实例sqlSessionFactory

4、DefaultListableBeanFactory\#findAutowireCandidates 通过调用beanNamesForTypeIncludingAncestors 返回的名字：sqlSessionFactory，再根据名字去getBean()去得到实例sqlSessionFactory。后返回`Map<String, Object> matchingBeans`集合

if (!isSelfReference(beanName, candidateName) && isAutowireCandidate(candidateName, descriptor)) { 
       result.put(candidateName, getBean(candidateName));
    }

5、BeanFactoryUtils\#beanNamesForTypeIncludingAncestors --> DefaultListableBeanFactory\#getBeanNamesForType --> DefaultListableBeanFactory\#doGetBeanNamesForType。根据类型得到beanName。此处类型为`org.apache.ibatis.session.SqlSessionFactory`，includeNonSingletons=true,allowEagerInit=true。最后返回的是beanName数组，此处数据大小为1，返回的beanName=sqlSessionFactory.

private String[] doGetBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit) { 
       List<String> result = new ArrayList<String>();
    
       // Check all bean definitions.
       for (String beanName : this.beanDefinitionNames) { 
          // Only consider bean as eligible if the bean name
          // is not defined as alias for some other bean.
          if (!isAlias(beanName)) { 
             try { 
                RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
                // Only check bean definition if it is complete.
                if (!mbd.isAbstract() && (allowEagerInit ||
                      ((mbd.hasBeanClass() || !mbd.isLazyInit() || isAllowEagerClassLoading())) &&
                            !requiresEagerInitForType(mbd.getFactoryBeanName()))) { 
                   // In case of FactoryBean, match object created by FactoryBean.
                   boolean isFactoryBean = isFactoryBean(beanName, mbd);
                   boolean matchFound = (allowEagerInit || !isFactoryBean || containsSingleton(beanName)) &&
                         (includeNonSingletons || isSingleton(beanName)) && isTypeMatch(beanName, type);
                   if (!matchFound && isFactoryBean) { 
                      // In case of FactoryBean, try to match FactoryBean instance itself next.
                      beanName = FACTORY_BEAN_PREFIX + beanName; //<---- FactoryBean做特殊处理，加'&'
                      matchFound = (includeNonSingletons || mbd.isSingleton()) && isTypeMatch(beanName, type); //此处对于studentMapper组装成有factoryBean来说，仍是false。
                   }
                   if (matchFound) { //最扣匹配成功的是beanName=sqlSessionFactory
                      result.add(beanName);
                   }
                }
             }
             //........
          }
       }
    
       // Check manually registered singletons too.
       //.... 
       return StringUtils.toStringArray(result);
    }

6、AbstractBeanFactory\#isTypeMatch(String name, ResolvableType typeToMatch)。 name=studentMapper, tryToMatch=org.apache.ibatis.session.SqlSessionFactory。 虽然下面getTypeForFactoryBean只是返回了factoryBean.getObjectType()，但在执行过程中，实例化了FactoryBean(studentMapper)。此处isTypeMatch返回的是false

如果是FactoryBean类型，那么我们想要看的是它创建的类，而不是FactoryBean类本身。

public boolean isTypeMatch(String name, ResolvableType typeToMatch) throws NoSuchBeanDefinitionException { 
        //......
        // Check bean class whether we're dealing with a FactoryBean.
        if (FactoryBean.class.isAssignableFrom(beanType)) { 
            if (!BeanFactoryUtils.isFactoryDereference(name)) { 
                // If it's a FactoryBean, we want to look at what it creates, not the factory class.
                beanType = getTypeForFactoryBean(beanName, mbd);
                if (beanType == null) { 
                    return false;
                }
            }    
        //.... 
        return typeToMatch.isAssignableFrom(beanType);    
    }

7、AbstractAutowireCapableBeanFactory\#getTypeForFactoryBean 在下面调用得到FactoryBean后，返回factoryBean.getObjectType()。getObjectType就FactoryBean的接口方法。

8、AbstractAutowireCapableBeanFactory\#getSingletonFactoryBeanForTypeCheck 得到下面调用返回的BeanWrapperImpl，并将它缓存起来。后返回FactoryBean对象。

> this.factoryBeanInstanceCache.put(beanName, bw); //bw即BeanWrapperImpl

9、ConstructorResolver\#autowireConstructor 通过SimpleInstantiationStrategy\#instantiate实例化MapperFactoryBean，并为BeanWrapperImpl的属性赋值，后返回BeanWrapperImpl。autowireConstructor 方法作用：构造函数注入:在这种模式下 ，Spring bean工厂能够宿主基于构造函数的组件依赖性解析。

10、SimpleInstantiationStrategy\#instantiate --> BeanUtils\#instantiateClass，通过反射构造函数创建MapperFactoryBean对象，mapperInterfacer的属性值为：interface com.paincupid.springmvc.persistence.StudentMapper

下面是实例化MapperFactoryBean（studentMapper）的全过程

<init>:65, MapperFactoryBean (org.mybatis.spring.mapper)
    newInstance0:-1, NativeConstructorAccessorImpl (sun.reflect)
    newInstance:62, NativeConstructorAccessorImpl (sun.reflect)
    newInstance:45, DelegatingConstructorAccessorImpl (sun.reflect)
    newInstance:422, Constructor (java.lang.reflect)
    instantiateClass:147, BeanUtils (org.springframework.beans)
    instantiate:122, SimpleInstantiationStrategy (org.springframework.beans.factory.support)
    autowireConstructor:267, ConstructorResolver (org.springframework.beans.factory.support)
    autowireConstructor:1143, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    createBeanInstance:1046, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    getSingletonFactoryBeanForTypeCheck:865, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    getTypeForFactoryBean:796, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    isTypeMatch:543, AbstractBeanFactory (org.springframework.beans.factory.support)
    doGetBeanNamesForType:447, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    getBeanNamesForType:423, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    beanNamesForTypeIncludingAncestors:220, BeanFactoryUtils (org.springframework.beans.factory)
    findAutowireCandidates:1130, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    doResolveDependency:1069, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    resolveDependency:967, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    autowireByType:1292, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    populateBean:1199, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    <--------------
    doCreateBean:543, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    createBean:482, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
    getObject:305, AbstractBeanFactory$1 (org.springframework.beans.factory.support)
    getSingleton:230, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support)
    doGetBean:301, AbstractBeanFactory (org.springframework.beans.factory.support)
    getBean:196, AbstractBeanFactory (org.springframework.beans.factory.support)
    preInstantiateSingletons:753, DefaultListableBeanFactory (org.springframework.beans.factory.support)
    finishBeanFactoryInitialization:834, AbstractApplicationContext (org.springframework.context.support)

# 八、其它补充 #

--------------------

## 8.1 Mapper接口对应的bean在容器中的数量 ##

Mapper在容器中是单例的，isSingleton()方法返回的是：true;

public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> { 
      @Override
      public boolean isSingleton() { 
        return true;
      }
    }

本文只涉及到部分Mybatis源码解析，以及mybatis-spring怎么把mybatis和spring整合起来，在事务中调用的。

还有很多mybatis的文章，可以参考：[Mybatis源码解析优秀博文][Mybatis]

[https_github.com_mybatis_mybatis-3]: https://github.com/mybatis/mybatis-3
[https_github.com_arthur-dy-lee_arthur-dy-lee-note]: https://github.com/arthur-dy-lee/arthur-dy-lee-note
[SqlSessionFactoryBean.png]: /images/20220413/d0c44159ac4f42f2b8d0994b843edca6.png
[MapperScannerConfigurer.png]: /images/20220413/49193cd90c8e4ca4bfdb7e5b9fee43ac.png
[beanDefinitions.png]: /images/20220413/72bc827b289c473f8ca7ed279c34fef3.png
[Image 1]: 
[MapperFactoryBean-instance.png]: /images/20220413/78136ff920874dcdb0f88d1cfe38e71a.png
[MapperRegistry.png]: /images/20220413/216f3d3ce2924c86aaba043fbd307654.png
[SqlSession.png]: /images/20220413/9e2cfb02473c47a09bcd6f41ab0a2e1e.png
[SimpleExecutor.png]: /images/20220413/9c92d7dab2864c01b2fce497a7a88600.png
[SqlSessionInterceptor.png]: /images/20220413/f449ea56d7c44e478b680a14bf38d107.png
[aopalliance]: http://aopalliance.sourceforge.net/
[SpringManagedTransactionFactory.png]: /images/20220413/91cb2abf50ed45709c033faee5598db3.png
[DataSourceTransactionManager.png]: /images/20220413/772c3fcd8dbc4cceb18bab6aee6c8103.png
[mybatis-trans-invoke1.png]: /images/20220413/4c19801fe8974caf9b1afcb7f250789a.png
[Mybatis]: https://blog.csdn.net/nmgrd/article/details/54608702