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：2020323

内容关于：Mybatis

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