Mybatis中SqlSession下的四大核心组件分析

SqlSession下的四大核心组件
Mybatis中SqlSession下的四大核心组件：ParameterHandler 、ResultSetHandler 、StatementHandler 、Executor 。

关注源码类： Configuration.java

//ParameterHandler 处理sql的参数对象
public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
    ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
    //包装参数插件
    parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
    return parameterHandler;
}

//ResultSetHandler 处理sql的返回结果集
public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds, ParameterHandler parameterHandler,
                                            ResultHandler resultHandler, BoundSql boundSql) {
    ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds);
    //包装返回结果插件
    resultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);
    return resultSetHandler;
}

//StatementHandler 数据库的处理对象
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);
    //包装数据库执行sql插件
    statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
    return statementHandler;
}

public Executor newExecutor(Transaction transaction) {
    //创建Mybatis的执行器：Executor
    return newExecutor(transaction, defaultExecutorType);
}

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
    //mybatis支持的三种执行器：batch、reuse、simple，其中默认支持的是simple
    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);
    }
    if (cacheEnabled) {
        executor = new CachingExecutor(executor);
    }
    //包装执行器插件
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
}

Mybatis的框架设计中，Mapper执行的过程中是通过Executor、ParameterHandler、StatementHandler、ResultHandler来完成数据库操作并返回处理结果的。