六、SqlSession 的创建过程以及 Executor 执行 SQL 过程详解

悠悠 2023-01-20 05:59 9阅读 0赞

*  源码地址：https://github.com/RononoaZoro/mybatis-book/tree/master 的 mybatis-book ( mybatis-chapter04 和 mybatis-chapter05)
 *  文章内容出自《Mybatis 3 源码深度解析》第五章
 *  自己实现代码地址：https://github.com/RononoaZoro/mybatis-book/tree/master 的 archer-mybatis

## 1、XPath 方式解析 XML 文件 ##

**users.xml**

<?xml version="1.0" encoding="UTF-8" ?>
    <users>
        <user id = "1">
            <name>张三</name>
            <createTime>2018-06-06 00:00:00</createTime>
            <passward>admin</passward>
            <phone>180000000</phone>
            <nickName>阿毛</nickName>
        </user>
        <user id = "2">
            <name>李四</name>
            <createTime>2018-06-06 00:00:00</createTime>
            <passward>admin</passward>
            <phone>180000001</phone>
            <nickName>明明</nickName>
        </user>
    </users>

**实体类 UserEntity**

package com.blog4java.mybatis.xpath;
    
    import lombok.Data;
    
    import java.util.Date;
    
    @Data
    public class UserEntity {
        
        private Long id;
        private String name;
        private Date createTime;
        private String password;
        private String phone;
        private String nickName;
    }

### 1）、XPath 解析 ###

package com.blog4java.mybatis.xpath;
    
    import com.alibaba.fastjson.JSON;
    import org.apache.commons.beanutils.BeanUtils;
    import org.apache.commons.beanutils.ConvertUtils;
    import org.apache.commons.beanutils.converters.DateConverter;
    import org.apache.ibatis.builder.BuilderException;
    import org.apache.ibatis.io.Resources;
    import org.junit.Test;
    import org.w3c.dom.Document;
    import org.w3c.dom.NodeList;
    
    import javax.xml.parsers.DocumentBuilder;
    import javax.xml.parsers.DocumentBuilderFactory;
    import javax.xml.xpath.XPath;
    import javax.xml.xpath.XPathConstants;
    import javax.xml.xpath.XPathFactory;
    import java.io.InputStream;
    import java.lang.reflect.InvocationTargetException;
    import java.util.ArrayList;
    import java.util.Date;
    import java.util.List;
    
    public class XPathExample {
        
    
        @Test
        public void testXPathParser() {
        
            try {
        
                // 创建DocumentBuilderFactory实例
                DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
                // 创建DocumentBuilder实例
                DocumentBuilder builder = factory.newDocumentBuilder();
                InputStream inputSource = Resources.getResourceAsStream("users.xml");
                Document doc = builder.parse(inputSource);
                // 获取XPath实例
                XPath xpath = XPathFactory.newInstance().newXPath();
                // 执行XPath表达式，获取节点信息
                NodeList nodeList = (NodeList)xpath.evaluate("/users/*", doc, XPathConstants.NODESET);
                List<UserEntity> userList = new ArrayList<>();
                for(int i=1; i < nodeList.getLength() + 1; i++) {
        
                    String path = "/users/user["+i+"]";
                    String id = (String)xpath.evaluate(path + "/@id", doc, XPathConstants.STRING);
                    String name = (String)xpath.evaluate(path + "/name", doc, XPathConstants.STRING);
                    String createTime = (String)xpath.evaluate(path + "/createTime", doc, XPathConstants.STRING);
                    String passward = (String)xpath.evaluate(path + "/passward", doc, XPathConstants.STRING);
                    String phone = (String)xpath.evaluate(path + "/phone", doc, XPathConstants.STRING);
                    String nickName = (String)xpath.evaluate(path + "/nickName", doc, XPathConstants.STRING);
                    // 调用buildUserEntity()方法，构建UserEntity对象
                    UserEntity userEntity = buildUserEntity(id,name, createTime, passward, phone, nickName);
                    userList.add(userEntity);
                }
                System.out.println(JSON.toJSONString(userList));
                System.out.println(userList.get(0).getCreateTime());
            } catch (Exception e) {
        
                throw new BuilderException("Error creating document instance.  Cause: " + e, e);
            }
        }
    
        private UserEntity buildUserEntity(String id,String name,
                                           String createTime, String passward,
                                           String phone, String nickName)
                throws IllegalAccessException, InvocationTargetException {
        
            UserEntity userEntity = new UserEntity();
            DateConverter dateConverter = new DateConverter(null);
            dateConverter.setPattern("yyyy-MM-dd HH:mm:ss");
            ConvertUtils.register(dateConverter,Date.class);
            BeanUtils.setProperty(userEntity,"id",id);
            BeanUtils.setProperty(userEntity,"name",name);
            BeanUtils.setProperty(userEntity,"createTime",createTime);
            BeanUtils.setProperty(userEntity,"passward",passward);
            BeanUtils.setProperty(userEntity,"phone",phone);
            BeanUtils.setProperty(userEntity,"nickName",nickName);
            return userEntity;
        }
    }

### 2）、Mybatis XNode 解析 ###

## 2、SqlSession 实例创建 ##

package com.blog4java.mybatis.sqlsession;
    
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    import org.junit.Test;
    
    import java.io.IOException;
    import java.io.Reader;
    
    public class SqlSessionExample {
        
    
        @Test
        public void testSqlSession() throws IOException {
        
            // 获取Mybatis配置文件输入流
            Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
            // 通过SqlSessionFactoryBuilder创建SqlSessionFactory实例
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
            // 调用SqlSessionFactory的openSession（）方法，创建SqlSession实例
            SqlSession session = sqlSessionFactory.openSession();
        }
    }

## 3、SqlSession 创建过程详解 ##

### 3.1、初始化 Configuration对象 ###

*  1）、**SqlSessionFactoryBuilder\#build** 方法中初始化了 Configuration 对象（参考：**五、Mybatis 核心对象之 Configuration 对象初始化详解**）
 *  2）、SqlSession 采用工厂模式创建，所以需要创建 SqlSessionFactory 对象，SqlSessionFactory 只有一个默认实现 DefaultSqlSessionFactory

// 通过SqlSessionFactoryBuilder创建SqlSessionFactory实例
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);

public class SqlSessionFactoryBuilder {
        
    
      public SqlSessionFactory build(Reader reader) {
        
        return build(reader, null, null);
      }
    
      public SqlSessionFactory build(Reader reader, String environment) {
        
        return build(reader, environment, null);
      }
    
      public SqlSessionFactory build(Reader reader, Properties properties) {
        
        return build(reader, null, properties);
      }
    
      public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
        
        try {
        
            
           //初始化 Configuration 对象
          XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
          return build(parser.parse());
            
        } catch (Exception e) {
        
          throw ExceptionFactory.wrapException("Error building SqlSession.", e);
        } finally {
        
          ErrorContext.instance().reset();
          try {
        
            reader.close();
          } catch (IOException e) {
        
            // Intentionally ignore. Prefer previous error.
          }
        }
      }
    }

### 3.2、创建 SqlSession 对象 ###

*  1）、SqlSession 是 Mybatis 提供的面向用户操作数据库的 API
 *  2）、SqlSession 默认实现是 DefaultSqlSession

// 调用SqlSessionFactory的openSession（）方法，创建SqlSession实例
    SqlSession session = sqlSessionFactory.openSession();

public class DefaultSqlSessionFactory implements SqlSessionFactory {
        
    
      private final Configuration configuration;
    
      public DefaultSqlSessionFactory(Configuration configuration) {
        
        this.configuration = configuration;
      }
    
      @Override
      public SqlSession openSession() {
        
        return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
      }
        
      private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
        
        Transaction tx = null;
        try {
        
          // 获取Mybatis主配置文件配置的环境信息
          final Environment environment = configuration.getEnvironment();
          // 创建事务管理器工厂
          final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
          // 创建事务管理器
          tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
          // 根据Mybatis主配置文件中指定的Executor类型创建对应的Executor实例
          final Executor executor = configuration.newExecutor(tx, execType);
          // 创建DefaultSqlSession实例
          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();
        }
      }
    }

*  3）、Executor 是真正用来执行 SQL 的执行器
 *  4）、默认执行器为 SimpleExecutor

final Executor executor = configuration.newExecutor(tx, execType);

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
        
        executorType = executorType == null ? defaultExecutorType : executorType;
        executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
        Executor executor;
        // 根据executor类型创建对象的Executor对象
        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);
        }
        // 如果cacheEnabled属性为ture，这使用CachingExecutor对上面创建的Executor进行装饰
        if (cacheEnabled) {
        
          executor = new CachingExecutor(executor);
        }
        // 执行拦截器链的拦截逻辑
        executor = (Executor) interceptorChain.pluginAll(executor);
        return executor;
      }

## 4、Executor 执行 SQL 过程详解 ##

*  1）、初始化 SqlSession 对象，并拿到 Configuration 对象
 *  2）、通过全路径获取 MappedStatement

package com.blog4java.mybatis.example;
    
    import com.alibaba.fastjson.JSON;
    import com.blog4java.common.DbUtils;
    import com.blog4java.mybatis.example.entity.UserEntity;
    import org.apache.ibatis.executor.Executor;
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.mapping.MappedStatement;
    import org.apache.ibatis.session.*;
    import org.apache.ibatis.transaction.jdbc.JdbcTransaction;
    import org.junit.Before;
    import org.junit.Test;
    
    import java.io.IOException;
    import java.io.InputStream;
    import java.sql.SQLException;
    import java.util.List;
    
    public class ExecutorExample {
        
    
        @Before
        public void initData() {
        
            DbUtils.initData();
        }
        @Test
        public void testExecutor() throws IOException, SQLException {
        
            // 获取配置文件输入流
            InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
            // 通过SqlSessionFactoryBuilder的build()方法创建SqlSessionFactory实例
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            // 调用openSession()方法创建SqlSession实例
            SqlSession sqlSession = sqlSessionFactory.openSession();
            Configuration configuration = sqlSession.getConfiguration();
            // 从Configuration对象中获取描述SQL配置的MappedStatement对象
            MappedStatement listAllUserStmt = configuration.getMappedStatement(
                    "com.blog4java.mybatis.com.blog4java.mybatis.example.mapper.UserMapper.listAllUser");
            //创建ReuseExecutor实例
            Executor reuseExecutor = configuration.newExecutor(
                    new JdbcTransaction(sqlSession.getConnection()),
                    ExecutorType.REUSE
            );
            // 调用query()方法执行查询操作
            List<UserEntity> userList =  reuseExecutor.query(listAllUserStmt,
                    null,
                    RowBounds.DEFAULT,
                    Executor.NO_RESULT_HANDLER);
            System.out.println(JSON.toJSON(userList));
        }
    
    
    }

*  2）创建 Executor 对象

//创建ReuseExecutor实例
    Executor reuseExecutor = configuration.newExecutor(
        new JdbcTransaction(sqlSession.getConnection()),
        ExecutorType.REUSE
    );

*  3）、执行获取结果

// 调用query()方法执行查询操作
    List<UserEntity> userList =  reuseExecutor.query(listAllUserStmt,null,RowBounds.DEFAULT,Executor.NO_RESULT_HANDLER);
    System.out.println(JSON.toJSON(userList));

**BaseExecutor**

@Override
      public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
        
        // 获取BoundSql对象，BoundSql是对动态SQL解析生成的SQL语句和参数映射信息的封装
        BoundSql boundSql = ms.getBoundSql(parameter);
        // 创建CacheKey，用于缓存Key
        CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);
        // 调用重载的query（）方法
        return query(ms, parameter, rowBounds, resultHandler, key, boundSql);
     }
    
     @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++;
          // 从缓存中获取结果
          list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
          if (list != null) {
        
            handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
          } else {
        
            // 缓存中获取不到，则调用queryFromDatabase（）方法从数据库中查询
            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;
      }
    
      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 {
        
          // 调用doQuery（）方法查询
          list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
        } finally {
        
          localCache.removeObject(key);
        }
        // 缓存查询结果
        localCache.putObject(key, list);
        if (ms.getStatementType() == StatementType.CALLABLE) {
        
          localOutputParameterCache.putObject(key, parameter);
        }
        return list;
      }
    
    
      protected abstract <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
          throws SQLException;

**SimpleExecutor**

@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();
          // 获取StatementHandler对象
          StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
          // 调用prepareStatement（）方法,创建Statement对象，并进行设置参数等操作
          stmt = prepareStatement(handler, ms.getStatementLog());
          // 调用StatementHandler对象的query（）方法执行查询操作
          return handler.<E>query(stmt, resultHandler);
        } finally {
        
          closeStatement(stmt);
        }
      }