mybatis插件(拦截器)

1、作用

可以在sql执行前后 结果映射 参数解析阶段做拦截处理（AOP）

如：日志打印 性能监控等

 

2、拦截的4个对象

Execute StatementHandle ParameterHandle ResultHandle

• Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)，主要用于sql重写。
• ParameterHandler (getParameterObject, setParameters)，用于参数处理。
• ResultSetHandler (handleResultSets, handleOutputParameters)，用于结果集二次处理。
• StatementHandler (prepare, parameterize, batch, update, query)，用于jdbc层的控制。

 

 

3、使用

定义哪个对象 哪个方法进行拦截

如：plugin方法返回代理对象

 

 

4、原理

具体的方法定义可以参见每个类方法的签名，这里就不详细展开了。这四个类被创建后不是直接返回，而是创执行了interceptorChain.pluginAll(parameterHandler)才返回。如下所示：

pluginAll最终调用每个拦截器的plugin方法，返回代理对象，如果有多个拦截器，就会一层层代理。

//Configuration 中
public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
    ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
    parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
    return parameterHandler;
}
​
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);
    resultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);
    return resultSetHandler;
}
​
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;
}
​
public Executor newExecutor(Transaction transaction) {
    return newExecutor(transaction, defaultExecutorType);
}
​
// Execute默认使用SimpleExecutor
public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
    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);
    }
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
}

5、总结

使用的设计模式：代理模式、责任链模式

参考：

https://www.cnblogs.com/chenpi/p/10498921.htm

https://www.cnblogs.com/zhjh256/p/11516878.html

https://my.oschina.net/u/4365042/blog/3344199l