ibatis源码分析

背景：调试模式下，单步运行一个查询订单协议操作，记录了ibatis框架的执行动作，侧面剖析其原理。

一、简介：

1. dal 层的dao接口实现类通常会继承SqlMapClientDaoSupport。spring容器在初始化一个dao bean实例时，通常会注入两块信息DataSource（数据源）和sqlMapClient（主要是sql语句），这两块信息会封装到SqlMapClientTemplate

2. 其中数据源的实例通常采用apache的开源项目dbcp

代码配置如下：

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> 
	<property name="driverClassName" value="com.mysql.jdbc.Driver" />
	<property name="url" value="xxxx" />
	<property name="username"><value>xxxx</value></property>
        <property name="password"><value>xxxxx</value></property>
        <property name="maxActive"><value>20</value></property>
        <property name="initialSize"><value>1</value></property>
        <property name="maxWait"><value>60000</value></property>
        <property name="maxIdle"><value>20</value></property>
        <property name="minIdle"><value>3</value></property>
        <property name="removeAbandoned"><value>true</value></property>
        <property name="removeAbandonedTimeout"><value>180</value></property>
        <property name="connectionProperties"><value>clientEncoding=GBK</value></property>
</bean>

各配置参数的具体含义可参照：dbcp基本配置和重连配置

3.sqlMapClient

<bean id="sqlMapClient" class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
		<property name="configLocation">
			<value>classpath:sqlmap.xml</value>
		</property>
	</bean>

	<bean id="sqlMapClientTddl" class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
		<property name="dataSource" ref="tGroupDataSource" />
		<property name="configLocation" value="classpath:sqlmap.xml"/>
	</bean>

sqlMapClient，主要是借助于实现FactoryBean和InitializingBean两个接口，加载sql.xml文件资源信息，得到sqlMapClient组件

注：上面的sqlMapClient默认不配置数据源，后面的SqlMapClientTemplate优先从全局变量中取，如果没有再从sqlMapClient中查找。

public DataSource getDataSource() {
		DataSource ds = super.getDataSource();
		return (ds != null ? ds : this.sqlMapClient.getDataSource());
	}

构造sqlMapClient组件的代码块。

public void afterPropertiesSet() throws Exception {
		if (this.lobHandler != null) {
			// Make given LobHandler available for SqlMapClient configuration.
			// Do early because because mapping resource might refer to custom types.
			configTimeLobHandlerHolder.set(this.lobHandler);
		}

		try {
			this.sqlMapClient = buildSqlMapClient(this.configLocations, this.mappingLocations, this.sqlMapClientProperties);

			// Tell the SqlMapClient to use the given DataSource, if any.
			if (this.dataSource != null) {
				TransactionConfig transactionConfig = (TransactionConfig) this.transactionConfigClass.newInstance();
				DataSource dataSourceToUse = this.dataSource;
				if (this.useTransactionAwareDataSource && !(this.dataSource instanceof TransactionAwareDataSourceProxy)) {
					dataSourceToUse = new TransactionAwareDataSourceProxy(this.dataSource);
				}
				transactionConfig.setDataSource(dataSourceToUse);
				transactionConfig.initialize(this.transactionConfigProperties);
				applyTransactionConfig(this.sqlMapClient, transactionConfig);
			}
		}

		finally {
			if (this.lobHandler != null) {
				// Reset LobHandler holder.
				configTimeLobHandlerHolder.set(null);
			}
		}
	}

4.SqlMapExecutor

该接口是对SQL操作行为的抽象，提供了SQL单条执行和批处理涉及的所有操作方法

5. SqlMapTransactionManager
该接口是对事务行为的抽象，提供了事务执行过程中涉及的所有方法。

6. SqlMapClient
该接口定位是SQL执行客户端，是线程安全的，用于处理多个线程的sql执行。它继承了上面两个接口，这意味着该接口具有SQL执行和事务处理的能力，该接口的核心实现类是SqlMapClientImpl。

7. SqlMapSession
该接口在继承关系上和SqlMapClient一致，但它的定位是保存单线程sql执行过程的session信息。该接口的核心实现类是SqlMapSessionImpl

8. MappedStatement
该接口定位是单条SQL执行时的上下文环境信息，如SQL标识、SQL、参数信息、返回结果、操作行为等。

9. ParameterMap/ResultMap
该接口用于在SQL执行的前后提供参数准备和执行结果集的处理。

整体类图：

二、具体调用

接下来就到了数据持久层的代码调用，所有的数据库DML操作（增、删、改、查）都是借助于SqlMapClientTemplate来实现的。

public OrderEnsureProtocolDO getOrderEnsureProtocolByOrderId(Long orderId) {
        if (orderId == null) {
            return null;
        }
        return (OrderEnsureProtocolDO) this.getSqlMapClientTemplate().queryForObject("MS-FIND-ORDERENSUREPROTOCOL-BY-ORDERID",
                                                                                     orderId);
    }

如果一次执行的sql较多，我们会采用批处理的形式

 public void batchDeleteOfferSaleRecord(final List<Long> orderEntryIds) throws Exception {
        if (orderEntryIds == null || orderEntryIds.size() < 1 || orderEntryIds.size() > 50) {
            return;
        }

        this.getSqlMapClientTemplate().execute(new SqlMapClientCallback() {

            @Override
            public Object doInSqlMapClient(SqlMapExecutor executor) throws SQLException {
                executor.startBatch();
                for (Long entryId : orderEntryIds) {
                    executor.insert(MS_DELETE_SALE_RECORD, entryId);
                }

                return executor.executeBatch();
            }
        });
    }

不管采用上面哪种方式，查看源代码会发现，最后都是在调用execute(SqlMapClientCallback action)方法

public Object queryForObject(final String statementName, final Object parameterObject)
			throws DataAccessException {

		return execute(new SqlMapClientCallback() {
			public Object doInSqlMapClient(SqlMapExecutor executor) throws SQLException {
				return executor.queryForObject(statementName, parameterObject);
			}
		});
	}

public Object execute(SqlMapClientCallback action) throws DataAccessException {
		Assert.notNull(action, "Callback object must not be null");
		Assert.notNull(this.sqlMapClient, "No SqlMapClient specified");
		//获取session信息(SqlMapSessionImpl实例)
		SqlMapSession session = this.sqlMapClient.openSession();
		if (logger.isDebugEnabled()) {
			logger.debug("Opened SqlMapSession [" + session + "] for iBATIS operation");
		}
		Connection ibatisCon = null;

		try {
			Connection springCon = null;//数据库连接
			DataSource dataSource = getDataSource();
			boolean transactionAware = (dataSource instanceof TransactionAwareDataSourceProxy);

			try {
			    //获取数据获连接
				ibatisCon = session.getCurrentConnection();
				if (ibatisCon == null) {
					springCon = (transactionAware ?
							dataSource.getConnection() : DataSourceUtils.doGetConnection(dataSource));
					//将数据源set到session会话中
					session.setUserConnection(springCon);
					if (logger.isDebugEnabled()) {
						logger.debug("Obtained JDBC Connection [" + springCon + "] for iBATIS operation");
					}
				}
				else {
					if (logger.isDebugEnabled()) {
						logger.debug("Reusing JDBC Connection [" + ibatisCon + "] for iBATIS operation");
					}
				}
			}
			catch (SQLException ex) {
				throw new CannotGetJdbcConnectionException("Could not get JDBC Connection", ex);
			}
			try {
				//执行SQL 
				return action.doInSqlMapClient(session);
			}
			catch (SQLException ex) {
				throw getExceptionTranslator().translate("SqlMapClient operation", null, ex);
			}
			finally {
				省略。。。一系列的关闭工作
		}
	}

SqlMapSessionImpl().queryForObject()的方法很简单，直接交给代理对象SqlMapExecutorDelegate处理（里面注入了很多功能对象，负责具体的sql执行）

  public Object queryForObject(String id, Object paramObject) throws SQLException {
    return delegate.queryForObject(session, id, paramObject);
  }

经过N层重载，最后调用内部的通用方法

  入参： 
  id=MS-FIND-ORDERENSUREPROTOCOL-BY-ORDERID
  paramObject=26749329
  
  public Object queryForObject(SessionScope session, String id, Object paramObject, Object resultObject) throws SQLException {
    Object object = null;

	//MappedStatement对象集是上文中提及的初始化方法SqlMapClientFactoryBean.afterPropertiesSet()中，由配置文件构建而成
	//调试中的ms为SelectStatement，具体的执行器
    MappedStatement ms = getMappedStatement(id); 
	// 用于事务执行
    Transaction trans = getTransaction(session); 
    boolean autoStart = trans == null;

    try {
      trans = autoStartTransaction(session, autoStart, trans);
	  // 从RequestScope池中获取该次sql执行中的上下文环境RequestScope 
      RequestScope request = popRequest(session, ms);  
      try {
	    // 执行sql
        object = ms.executeQueryForObject(request, trans, paramObject, resultObject);   
      } finally {
        pushRequest(request);  //归还RequestScope
      }

      autoCommitTransaction(session, autoStart);
    } finally {
      autoEndTransaction(session, autoStart);
    }

    return object;
  }

接下来由MappedStatement.executeQueryForObject()来执行

 public Object executeQueryForObject(RequestScope request, Transaction trans, Object parameterObject, Object resultObject)
      throws SQLException {
    try {
      Object object = null;

      DefaultRowHandler rowHandler = new DefaultRowHandler();
	   //执行sql语句
      executeQueryWithCallback(request, trans.getConnection(), parameterObject, resultObject, rowHandler, SqlExecutor.NO_SKIPPED_RESULTS, SqlExecutor.NO_MAXIMUM_RESULTS);
      
      //结果处理，返回结果
      List list = rowHandler.getList(); 
      if (list.size() > 1) {
        throw new SQLException("Error: executeQueryForObject returned too many results.");
      } else if (list.size() > 0) {
        object = list.get(0);
      }
    。。。。。。。。。
  }

MappedStatement.executeQueryWithCallback()方法包含了参数值映射、sql准备和sql执行等关键过程

  protected void executeQueryWithCallback(RequestScope request, Connection conn, Object parameterObject, Object resultObject, RowHandler rowHandler, int skipResults, int maxResults)
      throws SQLException {
	 //预先封装错误信息，如果报错时便于排查问题
    ErrorContext errorContext = request.getErrorContext();
    errorContext.setActivity("preparing the mapped statement for execution");
    errorContext.setObjectId(this.getId());
    errorContext.setResource(this.getResource());
    try {
	  //验证入参
      parameterObject = validateParameter(parameterObject);  

	  //获取SQL对象
      Sql sql = getSql();  

      errorContext.setMoreInfo("Check the parameter map.");
	  // 入参映射
      ParameterMap parameterMap = sql.getParameterMap(request, parameterObject);

      errorContext.setMoreInfo("Check the result map.");
	  //获取结果
      ResultMap resultMap = sql.getResultMap(request, parameterObject); 

      request.setResultMap(resultMap);
      request.setParameterMap(parameterMap);

      errorContext.setMoreInfo("Check the parameter map.");
	  //获取参数值
      Object[] parameters = parameterMap.getParameterObjectValues(request, parameterObject);  

      errorContext.setMoreInfo("Check the SQL statement.");
	  //获取拼装后的sql语句
      String sqlString = sql.getSql(request, parameterObject);  

      errorContext.setActivity("executing mapped statement");
      errorContext.setMoreInfo("Check the SQL statement or the result map.");
      RowHandlerCallback callback = new RowHandlerCallback(resultMap, resultObject, rowHandler);
	   //sql执行
      sqlExecuteQuery(request, conn, sqlString, parameters, skipResults, maxResults, callback); 

      ....省略
  }

最后调用com.ibatis.sqlmap.engine.execution.SqlExecutor.executeQuery(RequestScope, Connection, String, Object[], int, int, RowHandlerCallback)

  public void executeQuery(RequestScope request, Connection conn, String sql, Object[] parameters, int skipResults, int maxResults, RowHandlerCallback callback) throws SQLException {
    ...省略
    PreparedStatement ps = null;
    ResultSet rs = null;
    setupResultObjectFactory(request);
    try {
      errorContext.setMoreInfo("Check the SQL Statement (preparation failed).");
      Integer rsType = request.getStatement().getResultSetType();
      //初始化PreparedStatement，设置sql、参数值等
      if (rsType != null) {
        ps = prepareStatement(request.getSession(), conn, sql, rsType);
      } else {
        ps = prepareStatement(request.getSession(), conn, sql);
      }
      setStatementTimeout(request.getStatement(), ps);
      Integer fetchSize = request.getStatement().getFetchSize();
      if (fetchSize != null) {
        ps.setFetchSize(fetchSize.intValue());
      }
      errorContext.setMoreInfo("Check the parameters (set parameters failed).");
      request.getParameterMap().setParameters(request, ps, parameters);
      errorContext.setMoreInfo("Check the statement (query failed).");
	   //执行
      ps.execute();
      errorContext.setMoreInfo("Check the results (failed to retrieve results).");

      //结果集处理
      rs = handleMultipleResults(ps, request, skipResults, maxResults, callback);
      
      。。。省略

  }