Mybatis源码解析-Mybatis初始化过程

逃离我推掉我的手 2022-05-19 11:15 259阅读 0赞

# 测试方法 #

public class UserMapperTest { 
    
        private UserMapper userMapper;
    
        SqlSession sqlSession = null;
        SqlSessionFactory sqlSessionFactory = null;
    
        @Before
        public void setUp() throws Exception {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            //openSession(boolean autoCommit) 设置事务是否自动提交
            sqlSession = sqlSessionFactory.openSession(true);
            // 获取动态代理实现类
            this.userMapper = sqlSession.getMapper(UserMapper.class);
        }
    
        @Test
        public void testQueryUserById() {
            User user = userMapper.queryUserById(1L);
            System.out.println(user);
        }
    
        @Test
        public void testQueryAll() {
            List<User> users = userMapper.queryAll();
            for (User user : users) {
                System.out.println(user);
            }
        }
    }

SqlSessionFactoryBuilder 的 build 方法提供了对Reader和 InputStream 两种类型的支持，并提供了Resources类简化配置文件的读取。

public class SqlSessionFactoryBuilder { 
        public SqlSessionFactoryBuilder() {
        }
    
        public SqlSessionFactory build(Reader reader) {
            return this.build((Reader)reader, (String)null, (Properties)null);
        }
    
        public SqlSessionFactory build(Reader reader, String environment) {
            return this.build((Reader)reader, environment, (Properties)null);
        }
    
        public SqlSessionFactory build(Reader reader, Properties properties) {
            return this.build((Reader)reader, (String)null, properties);
        }
    
        public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
            SqlSessionFactory var5;
            try {
                XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
                var5 = this.build(parser.parse());
            } catch (Exception var14) {
                throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
            } finally {
                ErrorContext.instance().reset();
    
                try {
                    reader.close();
                } catch (IOException var13) {
                    ;
                }
    
            }
    
            return var5;
        }
    
        public SqlSessionFactory build(InputStream inputStream) {
            return this.build((InputStream)inputStream, (String)null, (Properties)null);
        }
    
        public SqlSessionFactory build(InputStream inputStream, String environment) {
            return this.build((InputStream)inputStream, environment, (Properties)null);
        }
    
        public SqlSessionFactory build(InputStream inputStream, Properties properties) {
            return this.build((InputStream)inputStream, (String)null, properties);
        }
        //通过XMLConfigBuilder解析配置文件构建SqlSessionFactory对象
        public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
            SqlSessionFactory var5;
            try {
                XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
                var5 = this.build(parser.parse());
            } catch (Exception var14) {
                throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
            } finally {
                ErrorContext.instance().reset();
    
                try {
                    inputStream.close();
                } catch (IOException var13) {
                    ;
                }
    
            }
    
            return var5;
        }
    
        public SqlSessionFactory build(Configuration config) {
            return new DefaultSqlSessionFactory(config);
        }
    }

# 解析过程 #

// XMLConfigBuilder
    public Configuration parse() {
        if (this.parsed) {
            throw new BuilderException("Each XMLConfigBuilder can only be used once.");
        } else {
            this.parsed = true;
            // 解析mybatis配置文件根结点configuration
            this.parseConfiguration(this.parser.evalNode("/configuration"));
            return this.configuration;
        }
    }
    // 解析mybatis核心配置文件的子节点信息(properties、settings、typeAliases、plugins、mappers...)
    private void parseConfiguration(XNode root) {
        try {
            // 解析properties节点
            this.propertiesElement(root.evalNode("properties"));
            // 解析settings节点
            Properties settings = this.settingsAsProperties(root.evalNode("settings"));
            this.loadCustomVfs(settings);
            // 解析typeAliases类型别名节点
            this.typeAliasesElement(root.evalNode("typeAliases"));
            // 解析plugin节点
            this.pluginElement(root.evalNode("plugins"));
            // 解析objectFactory节点
            this.objectFactoryElement(root.evalNode("objectFactory"));
            this.objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
            // 解析reflectorFactory节点
            this.reflectorFactoryElement(root.evalNode("reflectorFactory"));
            this.settingsElement(settings);
            // 解析environments节点
            this.environmentsElement(root.evalNode("environments"));
            this.databaseIdProviderElement(root.evalNode("databaseIdProvider"));
            this.typeHandlerElement(root.evalNode("typeHandlers"));
            // 解析mappers节点
            this.mapperElement(root.evalNode("mappers"));
        } catch (Exception var3) {
            throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + var3, var3);
        }
    }

## properties解析 ##

可通过resource或url属性引用外部资源文件(两者不能同时存在)，或使用property子元素配置

<properties resource="jdbc.properties"/>

解析properties配置

// XMLConfigBuilder
    private void propertiesElement(XNode context) throws Exception {
        if (context != null) {
            Properties defaults = context.getChildrenAsProperties(); // 获取所有的property子节点
            String resource = context.getStringAttribute("resource"); // 获取resource属性值
            String url = context.getStringAttribute("url"); // 获取url属性值
            if (resource != null && url != null) { //获取resource及url属性值 两者不能同时存在
                throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference. Please specify one or the other.");
            }
    
            if (resource != null) {
                defaults.putAll(Resources.getResourceAsProperties(resource)); // 将resource对应配置信息添加到defaults容器中
            } else if (url != null) {
                defaults.putAll(Resources.getUrlAsProperties(url)); // 将url对应配置信息添加到defaults容器中
            }
            //获取全局配置文件Configuration已有变量 并添加至defaults容器中
            Properties vars = this.configuration.getVariables();
            if (vars != null) {
                defaults.putAll(vars); 
            }
    
            this.parser.setVariables(defaults);
            this.configuration.setVariables(defaults); // 将proprties配置解析得到参数保存至全局配置类configuration的属性variables中
        }
    
    }

解析过程

*  首先解析properties的子节点property元素，将属性存入defaults容器。
 *  然后解析properties上面的resource或url属性（两者不能同时存在），解析外部配置文件并存入defaults容器。
 *  将defaults容器中所有配置信息添加到全局配置对象configuration中。

摘自mybatis官网

> 如果属性在不只一个地方进行了配置，那么MyBatis将按照下面的顺序来加载：  
> • 在 properties 元素体内指定的属性首先被读取。  
> • 然后根据 properties 元素中的 resource 属性读取类路径下属性文件或根据 url  
> • 最后读取作为方法参数传递的属性，并覆盖已读取的同名属性。。  
> 因此，通过方法参数传递的属性具有最高优先级，resource/url 属性中指定的配置文件次之，最低优先级的是 properties 属性中指定的属性。

## typeAliases解析 ##

可单独针对某个类型配置别名，也可以配置扫描包自动生成改包下所有类的别名(默认生成Bean首字母小写别名)

解析typeAliases配置

// XMLConfigBuilder
    private void typeAliasesElement(XNode parent) {
        if (parent != null) {
            Iterator var2 = parent.getChildren().iterator();
    
            while(var2.hasNext()) {
                XNode child = (XNode)var2.next();
                String alias;
                if ("package".equals(child.getName())) {
                    alias = child.getStringAttribute("name");
                    this.configuration.getTypeAliasRegistry().registerAliases(alias); //注册指定包下所有类
                } else {
                    alias = child.getStringAttribute("alias");
                    String type = child.getStringAttribute("type");
    
                    try {
                        Class<?> clazz = Resources.classForName(type);
                        if (alias == null) {
                            this.typeAliasRegistry.registerAlias(clazz);
                        } else {
                            this.typeAliasRegistry.registerAlias(alias, clazz); //指定单独类的别名
                        }
                    } catch (ClassNotFoundException var7) {
                        throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + var7, var7);
                    }
                }
            }
        }
    
    }

注册类型别名

// TypeAliasRegistry
    public void registerAliases(String packageName) { // 注册指定包的类型别名
        this.registerAliases(packageName, Object.class);
    }
    
    public void registerAliases(String packageName, Class<?> superType) {
        ResolverUtil<Class<?>> resolverUtil = new ResolverUtil();
        resolverUtil.find(new IsA(superType), packageName);
        Set<Class<? extends Class<?>>> typeSet = resolverUtil.getClasses();
        Iterator var5 = typeSet.iterator();
    
        while(var5.hasNext()) {
            Class<?> type = (Class)var5.next();
            if (!type.isAnonymousClass() && !type.isInterface() && !type.isMemberClass()) {
                this.registerAlias(type);
            }
        }
    
    }
    
    public void registerAlias(String alias, Class<?> value) { // 注册指定类的别名
        if (alias == null) {
            throw new TypeException("The parameter alias cannot be null");
        } else {
            String key = alias.toLowerCase(Locale.ENGLISH);
            if (this.TYPE_ALIASES.containsKey(key) && this.TYPE_ALIASES.get(key) != null && !((Class)this.TYPE_ALIASES.get(key)).equals(value)) {
                throw new TypeException("The alias '" + alias + "' is already mapped to the value '" + ((Class)this.TYPE_ALIASES.get(key)).getName() + "'.");
            } else {
                this.TYPE_ALIASES.put(key, value);
            }
        }
    }

## plugins解析 ##

> MyBatis 允许你在已映射语句执行过程中的某一点进行拦截调用。默认情况下，MyBatis 允许使用插件来拦截的方法调用包括：  
> • Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)  
> • ParameterHandler (getParameterObject, setParameters)  
> • ResultSetHandler (handleResultSets, handleOutputParameters)  
> • StatementHandler (prepare, parameterize, batch, update, query)

分页插件PageHelper配置

<plugins>
        <plugin interceptor="com.github.pagehelper.PageHelper">
            
            <property name="dialect" value="mysql"/>
            
            <property name="rowBoundsWithCount" value="true"/>
        </plugin>
    </plugins>

解析plugins配置

// XMLConfigBuilder
    private void pluginElement(XNode parent) throws Exception {
        if (parent != null) {
            Iterator var2 = parent.getChildren().iterator();
    
            while(var2.hasNext()) {
                XNode child = (XNode)var2.next();
                String interceptor = child.getStringAttribute("interceptor"); // 获取interceptor属性值
                Properties properties = child.getChildrenAsProperties();
                Interceptor interceptorInstance = (Interceptor)this.resolveClass(interceptor).newInstance(); // 创建Interceptor实例
                interceptorInstance.setProperties(properties); // 设置属性
                this.configuration.addInterceptor(interceptorInstance); //添加至Configuration的interceptorChain中
            }
        }
    
    }

## settings解析 ##

可以设置mybatis运行时行为，包括设置二级缓存、延迟加载、按需加载、经典命名到驼峰命名映射等（下面为常用属性）。

<table> 
 <thead> 
  <tr> 
   <th>设置参数</th> 
   <th align="center">描述</th> 
   <th align="right">有效值</th> 
   <th align="right">默认值</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>cacheEnabled</td> 
   <td align="center">全局地开启或关闭配置文件中的所有映射器已经配置的任何缓存。</td> 
   <td align="right">true|false</td> 
   <td align="right">true</td> 
  </tr> 
  <tr> 
   <td>lazyLoadingEnabled</td> 
   <td align="center">延迟加载的全局开关。当开启时，所有关联对象都会延迟加载。 特定关联关系中可通过设置fetchType属性来覆盖该项的开关状态。</td> 
   <td align="right">true|false</td> 
   <td align="right">false</td> 
  </tr> 
  <tr> 
   <td>aggressiveLazyLoading</td> 
   <td align="center">当开启时，任何方法的调用都会加载该对象的所有属性。否则，每个属性会按需加载（参考lazyLoadTriggerMethods).</td> 
   <td align="right">true|false</td> 
   <td align="right">false(true in ≤3.4.1)</td> 
  </tr> 
  <tr> 
   <td>mapUnderscoreToCamelCase</td> 
   <td align="center">是否开启自动驼峰命名规则（camel case）映射，即从经典数据库列名 A_COLUMN 到经典 Java 属性名 aColumn 的类似映射。</td> 
   <td align="right">true|false</td> 
   <td align="right">false</td> 
  </tr> 
 </tbody> 
</table>

Settings解析并添加至全局配置类Configuration

// XMLConfigBuilder
    private Properties settingsAsProperties(XNode context) {
        if (context == null) {
            return new Properties();
        } else {
            Properties props = context.getChildrenAsProperties();
            MetaClass metaConfig = MetaClass.forClass(Configuration.class, this.localReflectorFactory);
            Iterator var4 = props.keySet().iterator();
    
            Object key;
            do {
                if (!var4.hasNext()) {
                    return props;
                }
    
                key = var4.next();
            } while(metaConfig.hasSetter(String.valueOf(key)));
    
            throw new BuilderException("The setting " + key + " is not known. Make sure you spelled it correctly (case sensitive).");
        }
    }
    
    private void settingsElement(Properties props) throws Exception {
        this.configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));
        this.configuration.setAutoMappingUnknownColumnBehavior(AutoMappingUnknownColumnBehavior.valueOf(props.getProperty("autoMappingUnknownColumnBehavior", "NONE")));
        this.configuration.setCacheEnabled(this.booleanValueOf(props.getProperty("cacheEnabled"), true));
        this.configuration.setProxyFactory((ProxyFactory)this.createInstance(props.getProperty("proxyFactory")));
        this.configuration.setLazyLoadingEnabled(this.booleanValueOf(props.getProperty("lazyLoadingEnabled"), false)); 
        this.configuration.setAggressiveLazyLoading(this.booleanValueOf(props.getProperty("aggressiveLazyLoading"), false));
        this.configuration.setMultipleResultSetsEnabled(this.booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true));
        this.configuration.setUseColumnLabel(this.booleanValueOf(props.getProperty("useColumnLabel"), true));
        this.configuration.setUseGeneratedKeys(this.booleanValueOf(props.getProperty("useGeneratedKeys"), false));
        this.configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE")));
        this.configuration.setDefaultStatementTimeout(this.integerValueOf(props.getProperty("defaultStatementTimeout"), (Integer)null));
        this.configuration.setDefaultFetchSize(this.integerValueOf(props.getProperty("defaultFetchSize"), (Integer)null));
        this.configuration.setMapUnderscoreToCamelCase(this.booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false));
        this.configuration.setSafeRowBoundsEnabled(this.booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false));
        this.configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION")));
        this.configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER")));
        this.configuration.setLazyLoadTriggerMethods(this.stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString"));
        this.configuration.setSafeResultHandlerEnabled(this.booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true));
        this.configuration.setDefaultScriptingLanguage(this.resolveClass(props.getProperty("defaultScriptingLanguage")));
        Class<? extends TypeHandler> typeHandler = this.resolveClass(props.getProperty("defaultEnumTypeHandler"));
        this.configuration.setDefaultEnumTypeHandler(typeHandler);
        this.configuration.setCallSettersOnNulls(this.booleanValueOf(props.getProperty("callSettersOnNulls"), false));
        this.configuration.setUseActualParamName(this.booleanValueOf(props.getProperty("useActualParamName"), true));
        this.configuration.setReturnInstanceForEmptyRow(this.booleanValueOf(props.getProperty("returnInstanceForEmptyRow"), false));
        this.configuration.setLogPrefix(props.getProperty("logPrefix"));
        Class<? extends Log> logImpl = this.resolveClass(props.getProperty("logImpl"));
        this.configuration.setLogImpl(logImpl);
        this.configuration.setConfigurationFactory(this.resolveClass(props.getProperty("configurationFactory")));
    }

## mappers解析 ##

mappers定义了mapper映射文件位置，可以使用类路径、url、全局类名或配置扫描包来引入。

mapper解析流程

// XMLConfigBuilder
    private void mapperElement(XNode parent) throws Exception {
        if (parent != null) {
            Iterator var2 = parent.getChildren().iterator();
    
            while(true) {
                while(var2.hasNext()) {
                    XNode child = (XNode)var2.next();
                    String resource;
                    if ("package".equals(child.getName())) { // 如果是package子节点
                        resource = child.getStringAttribute("name"); // 获取package节点的name属性值(mapper class的包路径)
                        this.configuration.addMappers(resource); // 将所有的mapper class添加到configuration的mapperRegistry容器中
                    } else {
                // mapper子节点 获取resource、url、class属性值
                        resource = child.getStringAttribute("resource");
                        String url = child.getStringAttribute("url");
                        String mapperClass = child.getStringAttribute("class");
                        XMLMapperBuilder mapperParser;
                        InputStream inputStream;
                        if (resource != null && url == null && mapperClass == null) { // 配置了resource属性
                            ErrorContext.instance().resource(resource);
                            inputStream = Resources.getResourceAsStream(resource);
                // 使用XMLMapperBuilder解析mapper配置文件 并注册到configuration的mapperRegistry容器中
                            mapperParser = new XMLMapperBuilder(inputStream, this.configuration, resource, this.configuration.getSqlFragments());
                            mapperParser.parse();
                        } else if (resource == null && url != null && mapperClass == null) { // 配置了url属性
                            ErrorContext.instance().resource(url);
                            inputStream = Resources.getUrlAsStream(url);
                            mapperParser = new XMLMapperBuilder(inputStream, this.configuration, url, this.configuration.getSqlFragments());
                            mapperParser.parse();
                        } else { // 配置了class属性
                            if (resource != null || url != null || mapperClass == null) {
                                throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
                            }
    
                            Class<?> mapperInterface = Resources.classForName(mapperClass); // 将全限定名转换为Class对象
                            this.configuration.addMapper(mapperInterface); // 注册到configuration的mapperRegistry容器中
                        }
                    }
                }
    
                return;
            }
        }
    }

// XMLMapperBuilder
    private XMLMapperBuilder(XPathParser parser, Configuration configuration, String resource, Map<String, XNode> sqlFragments) {
        super(configuration); // 将configuration赋值给BaseBuilder维护的全局configuration 
        this.builderAssistant = new MapperBuilderAssistant(configuration, resource); // 创建MapperBuilderAssistant对象
        this.parser = parser;
        this.sqlFragments = sqlFragments;
        this.resource = resource;
    }
    
    // 解析mapper文件
    public void parse() {
        if (!this.configuration.isResourceLoaded(this.resource)) { // 若当前mapper还未加载 则执行解析
            this.configurationElement(this.parser.evalNode("/mapper")); // 解析mapper配置元素
            this.configuration.addLoadedResource(this.resource); // 添加到configuration的loadedResources容器
            this.bindMapperForNamespace(); // 将当前mapper文件注册到configuration的mapperRegistry容器中
        }
    
        this.parsePendingResultMaps();
        this.parsePendingCacheRefs();
        this.parsePendingStatements();
    }

configurationElement方法

// XMLMapperBuilder
    private void configurationElement(XNode context) {
        try {
            String namespace = context.getStringAttribute("namespace");
            if (namespace != null && !namespace.equals("")) {
                this.builderAssistant.setCurrentNamespace(namespace); // 将namespace设置到MapperBuilderAssistant中
                this.cacheRefElement(context.evalNode("cache-ref")); // 解析cache-ref节点
                this.cacheElement(context.evalNode("cache")); // 解析cache节点
                this.parameterMapElement(context.evalNodes("/mapper/parameterMap")); // 解析parameterMap节点
                this.resultMapElements(context.evalNodes("/mapper/resultMap")); // 解析resultMap
                this.sqlElement(context.evalNodes("/mapper/sql")); // 解析sql节点
                this.buildStatementFromContext(context.evalNodes("select|insert|update|delete")); // 解析具体sql节点
            } else {
                throw new BuilderException("Mapper's namespace cannot be empty");
            }
        } catch (Exception var3) {
            throw new BuilderException("Error parsing Mapper XML. The XML location is '" + this.resource + "'. Cause: " + var3, var3);
        }
    }

// XMLMapperBuilder
    private void resultMapElements(List<XNode> list) throws Exception {
        Iterator var2 = list.iterator();
    
        while(var2.hasNext()) {
            XNode resultMapNode = (XNode)var2.next();
    
            try {
                this.resultMapElement(resultMapNode);
            } catch (IncompleteElementException var5) {
                ;
            }
        }
    
    }
    
    private ResultMap resultMapElement(XNode resultMapNode) throws Exception {
        return this.resultMapElement(resultMapNode, Collections.emptyList());
    }
    // 解析resultMap节点
    private ResultMap resultMapElement(XNode resultMapNode, List<ResultMapping> additionalResultMappings) throws Exception {
        ErrorContext.instance().activity("processing " + resultMapNode.getValueBasedIdentifier());
        String id = resultMapNode.getStringAttribute("id", resultMapNode.getValueBasedIdentifier()); // 获取resultMap节点的id属性
        // 获取resultMap节点的type属性
        String type = resultMapNode.getStringAttribute("type", resultMapNode.getStringAttribute("ofType", resultMapNode.getStringAttribute("resultType", resultMapNode.getStringAttribute("javaType"))));
        String extend = resultMapNode.getStringAttribute("extends"); // 获取resultMap节点的extends属性
        Boolean autoMapping = resultMapNode.getBooleanAttribute("autoMapping"); // 获取resultMap节点的autoMapping属性
        Class<?> typeClass = this.resolveClass(type); // 将返回值类型转换为Class对象
        Discriminator discriminator = null;
        List<ResultMapping> resultMappings = new ArrayList(); 
        resultMappings.addAll(additionalResultMappings); // 添加到resultMappings集合（存储resultMap的子节点）
        List<XNode> resultChildren = resultMapNode.getChildren();
        Iterator var11 = resultChildren.iterator();
    
        while(var11.hasNext()) {
            XNode resultChild = (XNode)var11.next();
            if ("constructor".equals(resultChild.getName())) { // 解析constructor节点的子节点并添加resultMappings集合中
                this.processConstructorElement(resultChild, typeClass, resultMappings);
            } else if ("discriminator".equals(resultChild.getName())) { // 解析discriminator节点的子节点并添加resultMappings集合中
                discriminator = this.processDiscriminatorElement(resultChild, typeClass, resultMappings);
            } else { 
                List<ResultFlag> flags = new ArrayList();
                if ("id".equals(resultChild.getName())) {
                    flags.add(ResultFlag.ID);
                }
    
                resultMappings.add(this.buildResultMappingFromContext(resultChild, typeClass, flags));
            }
        }
    
        ResultMapResolver resultMapResolver = new ResultMapResolver(this.builderAssistant, id, typeClass, extend, discriminator, resultMappings, autoMapping);
    
        try {
            return resultMapResolver.resolve();
        } catch (IncompleteElementException var14) {
            this.configuration.addIncompleteResultMap(resultMapResolver);
            throw var14;
        }
    }

将sql语句解析为MappedStatement对象，并添加到全局configuration中

// XMLMapperBuilder
    private void buildStatementFromContext(List<XNode> list) {
        if (this.configuration.getDatabaseId() != null) {
            this.buildStatementFromContext(list, this.configuration.getDatabaseId());
        }
    
        this.buildStatementFromContext(list, (String)null);
    }
    
    private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
        Iterator var3 = list.iterator();
    
        while(var3.hasNext()) {
            XNode context = (XNode)var3.next();
            XMLStatementBuilder statementParser = new XMLStatementBuilder(this.configuration, this.builderAssistant, context, requiredDatabaseId);
    
            try {
                statementParser.parseStatementNode();
            } catch (IncompleteElementException var7) {
                this.configuration.addIncompleteStatement(statementParser);
            }
        }
    
    }

// XMLStatementBuilder
    public void parseStatementNode() {
        String id = this.context.getStringAttribute("id");
        String databaseId = this.context.getStringAttribute("databaseId");
        if (this.databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
            Integer fetchSize = this.context.getIntAttribute("fetchSize");
            Integer timeout = this.context.getIntAttribute("timeout");
            String parameterMap = this.context.getStringAttribute("parameterMap");
            String parameterType = this.context.getStringAttribute("parameterType");
            Class<?> parameterTypeClass = this.resolveClass(parameterType);
            String resultMap = this.context.getStringAttribute("resultMap");
            String resultType = this.context.getStringAttribute("resultType");
            String lang = this.context.getStringAttribute("lang");
            LanguageDriver langDriver = this.getLanguageDriver(lang);
            Class<?> resultTypeClass = this.resolveClass(resultType);
            String resultSetType = this.context.getStringAttribute("resultSetType");
            StatementType statementType = StatementType.valueOf(this.context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
            ResultSetType resultSetTypeEnum = this.resolveResultSetType(resultSetType);
            String nodeName = this.context.getNode().getNodeName();
            SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
            boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
            boolean flushCache = this.context.getBooleanAttribute("flushCache", !isSelect);
            boolean useCache = this.context.getBooleanAttribute("useCache", isSelect);
            boolean resultOrdered = this.context.getBooleanAttribute("resultOrdered", false);
            XMLIncludeTransformer includeParser = new XMLIncludeTransformer(this.configuration, this.builderAssistant);
            includeParser.applyIncludes(this.context.getNode());
            this.processSelectKeyNodes(id, parameterTypeClass, langDriver);
            SqlSource sqlSource = langDriver.createSqlSource(this.configuration, this.context, parameterTypeClass);
            String resultSets = this.context.getStringAttribute("resultSets");
            String keyProperty = this.context.getStringAttribute("keyProperty");
            String keyColumn = this.context.getStringAttribute("keyColumn");
            String keyStatementId = id + "!selectKey";
            keyStatementId = this.builderAssistant.applyCurrentNamespace(keyStatementId, true);
            Object keyGenerator;
            if (this.configuration.hasKeyGenerator(keyStatementId)) {
                keyGenerator = this.configuration.getKeyGenerator(keyStatementId);
            } else {
                keyGenerator = this.context.getBooleanAttribute("useGeneratedKeys", this.configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType)) ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
            }
            // 使用MapperBuilderAssistant辅助类添加MappedStatement
            this.builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType, fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass, resultSetTypeEnum, flushCache, useCache, resultOrdered, (KeyGenerator)keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
        }
    }

解析完成后会返回configuration对象，通过build(configuration)方法创建一个DefaultSqlSessionFactory

// SqlSessionFactoryBuilder
    public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
        SqlSessionFactory var5;
        try {
            XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
            var5 = this.build(parser.parse());
        } catch (Exception var14) {
            throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
        } finally {
            ErrorContext.instance().reset();
    
            try {
                inputStream.close();
            } catch (IOException var13) {
                ;
            }
    
        }
    
        return var5;
    }
    
    public SqlSessionFactory build(Configuration config) {
        return new DefaultSqlSessionFactory(config); // 创建默认实现DefaultSqlSessionFactory
    }

自此，mybatis的初始化过程完成。

# 参考资料 #

[http://www.mybatis.org/mybatis-3/zh/configuration.html][http_www.mybatis.org_mybatis-3_zh_configuration.html]  
[https://www.jianshu.com/p/7bc6d3b7fb45][https_www.jianshu.com_p_7bc6d3b7fb45]  
[http://www.cnblogs.com/dongying/tag/Mybatis%E6%B7%B1%E5%85%A5%E6%B5%85%E5%87%BA%E7%B3%BB%E5%88%97/][http_www.cnblogs.com_dongying_tag_Mybatis_E6_B7_B1_E5_85_A5_E6_B5_85_E5_87_BA_E7_B3_BB_E5_88_97]

[http_www.mybatis.org_mybatis-3_zh_configuration.html]: http://www.mybatis.org/mybatis-3/zh/configuration.html
[https_www.jianshu.com_p_7bc6d3b7fb45]: https://www.jianshu.com/p/7bc6d3b7fb45
[http_www.cnblogs.com_dongying_tag_Mybatis_E6_B7_B1_E5_85_A5_E6_B5_85_E5_87_BA_E7_B3_BB_E5_88_97]: http://www.cnblogs.com/dongying/tag/Mybatis%E6%B7%B1%E5%85%A5%E6%B5%85%E5%87%BA%E7%B3%BB%E5%88%97/