Mybatis源码学习第七天(插件开发原理)

插件概述:

插件是用来改变或者扩展mybatis的原有功能,mybatis的插件就是通过继承Interceptor拦截器实现的,在没有完全理解插件之前j禁止使用插件对mybatis进行扩展,有可能会导致严重的问题;

mybatis中能使用插件进行拦截的接口和方法如下:

Executor(update,query,flushStatement,commit,rollback,getTransation,close,isClose);

StatementHandler(prepare,parameterize,batch,update,query);

ParameterHandler(getParameterObject,setParameters);

ResultSetHandler(handleResultSets.handleCursorResultSets,handleOutputParameters);

插件实现步骤:

1:实现Interceptor接口方法

2:确定拦截的签名

3:在配置文件中配置插件

4:运行测试用例

本来不打算写的,后来想想写一个吧;

先看一下接口;

 /**
  *    Copyright 2009-2019 the original author or authors.
  *
  *    Licensed under the Apache License, Version 2.0 (the "License");
  *    you may not use this file except in compliance with the License.
  *    You may obtain a copy of the License at
  *
  *       http://www.apache.org/licenses/LICENSE-2.0
  *
  *    Unless required by applicable law or agreed to in writing, software
  *    distributed under the License is distributed on an "AS IS" BASIS,
  *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *    See the License for the specific language governing permissions and
  *    limitations under the License.
  */
 package org.apache.ibatis.plugin;

 import java.util.Properties;

 /**
  * @author Clinton Begin
  */
 public interface Interceptor {

   /**
    * 执行拦截逻辑的方法
    * @param invocation
    * @return
    * @throws Throwable
    */
   Object intercept(Invocation invocation) throws Throwable;

   /**
    *
    * @param target 被拦截的对象,他的作用就是给拦截的对象生成一个代理对象
    * @return
    */
   default Object plugin(Object target) {
     return Plugin.wrap(target, this);
   }

   /**
    * 读取 在plugin中设置的参数
    * @param properties
    */
   default void setProperties(Properties properties) {
     // NOP
   }

 }

手写慢SQL插件拦截器

 package org.apache.ibatis.plugin.impl;

 import org.apache.ibatis.executor.statement.StatementHandler;
 import org.apache.ibatis.logging.jdbc.PreparedStatementLogger;
 import org.apache.ibatis.plugin.Interceptor;
 import org.apache.ibatis.plugin.Intercepts;
 import org.apache.ibatis.plugin.Invocation;
 import org.apache.ibatis.plugin.Signature;
 import org.apache.ibatis.reflection.MetaObject;
 import org.apache.ibatis.reflection.SystemMetaObject;
 import org.apache.ibatis.session.ResultHandler;

 import java.sql.PreparedStatement;
 import java.sql.Statement;
 import java.util.Properties;

 /**
  * @Description 慢SQL查询日志拦截器
  * @ClassName ThresholdInterceptor
  * @Author mr.zhang
  * @Date 2020/3/23 21:35
  * @Version 1.0.0
  **/

 /**
  * 定义拦截位置
  * 参数解释:
  *  type:拦截的类
  *  method:该类的那个方法
  *  args:该方法的参数
  */
 @Intercepts({
   @Signature(type = StatementHandler.class, method = "query", args = {Statement.class,ResultHandler.class})
 })
 public class ThresholdInterceptor implements Interceptor {

   // 时间阈值
   private Long threshold;

   @Override
   public Object intercept(Invocation invocation) throws Throwable {
     long begin = System.currentTimeMillis();
     Object proceed = invocation.proceed();
     long end = System.currentTimeMillis();
     long runTime = end - begin;
     // 如果大于等于阈值那么记录慢SQL
     if(runTime>=threshold){
       // 获取参数
       Object[] args = invocation.getArgs();
       // 根据方法参数可得知第0个是Statement
       Statement stmt = (Statement) args[0];
       // 通过反射转化为metaObject
       MetaObject metaObject = SystemMetaObject.forObject(stmt);
       // getValue("h")是因为在动态代理中存在的InvocationHandler就是h
       // protected InvocationHandler h; 在Proxy类中定义的 在动态代理生成代理类时都会存在
       PreparedStatementLogger preparedStatementLogger = (PreparedStatementLogger) metaObject.getValue("h");
       PreparedStatement preparedStatement = preparedStatementLogger.getPreparedStatement();
       System.out.println("Sql语句:“"+preparedStatement.toString()+"”执行时间为:"+runTime+"毫秒,已经超过阈值!");
     }

     return proceed;
   }

   @Override
   public void setProperties(Properties properties) {
     this.threshold = Long.valueOf(properties.getProperty("threshold"));
   }
 }

如果需要使用在mybatis-config.xml 的plugins中配置就可以了,记得配置阈值哦;

作者：彼岸舞

时间：2020\03\23

内容关于：Mybatis

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