读mybatis源码之八：声明处理器StatementHandler

在执行器中，都会获取声明处理器：

public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
    statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
    return statementHandler;
  }

statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);

使用拦截器，声明处理可以定义插件

使用路由声明处理器，可以获取SimpleStatementHandler、PreparedStatementHandler、CallableStatementHandler三大处理器。

到底使用哪个处理器，是由ms.getStatementType参数决定，默认是mappedStatement.statementType = StatementType.PREPARED;

在mapper里面的执行语句 xml标签中可以配置statementType属性：

Any one of STATEMENT, PREPARED or CALLABLE. This causes MyBatis to use Statement, PreparedStatement or CallableStatement 

respectively. Default: PREPARED.

BaseStatementHandler

声明处理器基类，主要是产生 :

protected final TypeHandlerRegistry typeHandlerRegistry; //类型处理注册

protected final ResultSetHandler resultSetHandler;  //结果处理

protected final ParameterHandler parameterHandler; //参数处理

另外还准备Statement，具体由各个处理器生成instantiateStatement