StatementHandler负责操作Statement对象和与数据库进行通信。ParameterHandler和ResultSetHandler也用于分配参数和映射结果集。1、StatementHandler中的主要方法是Statementprepare(Connectionconnection)throwsSQLException；voidparameterize(Statementstatement)抛出SQLException；int更新（语句语句）抛出SQLException；Listquery(Statementstatement,ResultHandlerresultHandler)throwsSQLException;prepare：用于创建Statement实例参数size：赋值给sql占位符update：用于通知Statement对象推送插入、更新、删除operationstothedatabasequery：用于通知Statement对象将select操作推送到数据库，并返回相应的查询结果RoutingStatementHandler：StatementHandler接口的默认实现，根据StatementType获取真正的StatementHandler，然后赋值给属性delegatepublicStatementHandlernewStatementHandler(Executorexecutor,MappedStatementmappedStatement,ObjectparameterObject,RowBoundsrowBounds,ResultHandlerresultHandler,BoundSqlboundSql){StatementHandlerstatementHandler=newRoutingStatementHandler(executor,mappedStatement,parameterObject,rowBounds,resultHandler,boundSql);StatementHandlerstatementHandler=(StatementHandler)this.interceptorChain.pluginAll(statementHandler);返回statementHandler;}publicRoutingStatementHandler(Executorexecutor,MappedStatementms,Objectparameter,RowBoundsrowBounds,ResultHandlerresultHandler,BoundSqlboundSql){switch(ms.getStatementType()){caseSTATEMENT:delegate=newSimpleStatementHandler(executor,ms,parameter,rowBounds,结果处理程序,boundSql);休息;casePREPARED:delegate=newPreparedStatementHandler(executor,ms,parameter,rowBounds,resultHandler,boundSql);休息;caseCALLABLE:delegate=newCallableStatementHandler(executor,ms,parameter,rowBounds,resultHandler,boundSql);休息;默认值：抛出新的ExecutorException("未知语句类型："+ms.getStatementType());}}BaseStatementHandler的三个实现类：SimpleStatementHandler：处理不需要预编译的sql，（不需要处理参数的sql）PreparedStatementHandler：处理需要预编译的sql（解析xml时指定StatementType为Prepared，所以被使用default)CallableStatementHandler：调用存储过程只会在操作数据库（select、update）时得到StatementHandler对象，所以由Executor管理和创建。以SimpleExecutor为例分析生成StatementHandler和Statement的源码try{配置configuration=ms.getConfiguration();StatementHandlerhandler=configuration.newStatementHandler(wrapper,ms,parameter,rowBounds,resultHandler,boundSql);//获取Statement对象stmt=prepareStatement(handler,ms.getStatementLog());返回处理程序。查询（stmt，resultHandler）；}最后{关闭语句（stmt）；}}获取Statement实例源码分析privateStatementprepareStatement(StatementHandlerhandler,LogstatementLog)throwsSQLException{Statementstmt;连接connection=getConnection(statementLog);//获取Statement实例stmt=handler.prepare(connection,transaction.getTimeout());//stmt进行参数处理//SimpleStatementHandler中的parameterize是一个空方法，因为它只处理简单的sql，带参数的sql由PreparedStatementHandler处理handler.parameterize(stmt);返回stmt；}//调用RoutingStatementHandler方法中的方法，本质上是调用了属性delegate的prepare方法//delegate的赋值上面说了publicStatementprepare(Connectionconnection,IntegertransactionTimeout)throwsSQLException{returndelegate.prepare(连接，事务超时）；}//在BaseStatementHandler中调用preparepublicStatementprepare(Connectionconnection,IntegertransactionTimeout)throwsSQLException{ErrorContext.instance().sql(boundSql.getSql());语句语句=无效的;try{//由子类提供实例statement=instantiateStatement(connection);setStatementTimeout（声明，交易超时）；setFetchSize（声明）；返回声明；}//SimpleStatementHandler提供的实际保护语句instantiateStatement(Connectionconnection)throwsSQLException{if(mappedStatement.getResultSetType()=null){returnconnection.createStatement(mappedStatement.getResultSetType().getValue(),ResultSet.CONCUR_READ_ONLY);}else{returnconnection.createStatement();}}
