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：Executorreturn 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simpleif (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。
