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MyBatisr如何模拟生成Mapper代理对象

news 2026/6/5 22:53:49

MyBatis操作数据库使用Mapper接口和XML SQL定义，并没有创建接口实现类，MyBatis如何为Mapper接口生成代理对象的，MyBatis使用JDK proxy或Cglib生成一个代理对象，在org.apache.ibatis.session.SqlSession方法中扫描Mapper和XML完成对数据库操作。

本例通过两种方式演示MyBatis生成代理工作原理，
一是按照MyBatis规范设计Mapper接口和XML定义，自定义代理生成类MapperProxy，使用SqlSession触发方法。

TestMapper.xml<?xml version="1.0"encoding="UTF-8"?><!DOCTYPEmapperPUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.hk.mapper.TestMapper"><resultMap id="UserMap"type="com.hk.entity.UserInfo"><result column="id"property="id"/><result column="name"property="name"/><result column="login_id"property="loginId"/><result column="pwd"property="pwd"/><result column="version"property="version"/><result column="status"property="status"/><result column="org_name"property="orgName"/></resultMap><select id="getUserList"parameterType="String"resultType="com.hk.entity.UserInfo">select u.* from user u</select></mapper>TestMapper.javapackagecom.hk.mybatis;importcom.baomidou.mybatisplus.core.conditions.Wrapper;importcom.baomidou.mybatisplus.core.mapper.BaseMapper;importcom.baomidou.mybatisplus.core.metadata.IPage;importcom.baomidou.mybatisplus.core.toolkit.Constants;importcom.hk.entity.UserInfo;importorg.apache.ibatis.annotations.Mapper;importorg.apache.ibatis.annotations.Param;importjava.util.List;publicinterfaceTestMapperextendsBaseMapper<UserInfo>{publicList<UserInfo>getUserList();publicList<UserInfo>getUserByName(@Param("name")Stringname);}MapperProxy.javapackagecom.hk.mybatis;importorg.apache.ibatis.session.SqlSession;importjava.io.Serializable;importjava.lang.reflect.InvocationHandler;importjava.lang.reflect.Method;importjava.sql.*;importjava.util.ArrayList;importjava.util.HashMap;importjava.util.List;importjava.util.Map;publicclassMapperProxy<T>implementsInvocationHandler,Serializable{privatestaticfinallongserialVersionUID=-6424540398559729838L;privateSqlSessionsqlSession;privatefinalClass<T>mapperInterface;publicMapperProxy(SqlSessionsqlSession,Class<T>mapperInterface){this.sqlSession=sqlSession;this.mapperInterface=mapperInterface;}@OverridepublicObjectinvoke(Objectproxy,Methodmethod,Object[]args)throwsThrowable{if(Object.class.equals(method.getDeclaringClass())){// Object 提供的toString、hashCode等不需要代理执行returnmethod.invoke(this,args);}else{returnsqlSession.selectList(method.getName(),args);// 代理映射最终执行是 SqlSession}}}MapperProxyFactory.javapackagecom.hk.mybatis;importorg.apache.ibatis.session.SqlSession;importjava.lang.reflect.Proxy;importjava.util.Map;publicclassMapperProxyFactory<T>{privatefinalClass<T>mapperInterface;publicMapperProxyFactory(Class<T>mapperInterface){this.mapperInterface=mapperInterface;}publicTnewInstance(SqlSessionsqlSession){finalMapperProxy<T>mapperProxy=newMapperProxy<>(sqlSession,mapperInterface);// 注意：接口在扫描时通过ClassScanner.scanPackage()加载为了一个Java类return(T)Proxy.newProxyInstance(mapperInterface.getClassLoader(),newClass[]{mapperInterface},mapperProxy);// 传入类加载器、接口的类对象，代理目标类，创建 JDK 动态代理对象}}MapperProxyFactoryTest.javapackagecom.hk.mybatis;importcom.hk.Starter;importcom.hk.entity.UserInfo;importcom.hk.mapper.UserMapper;importorg.apache.ibatis.session.SqlSessionFactory;importorg.junit.Test;importorg.junit.runner.RunWith;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.boot.test.context.SpringBootTest;importorg.springframework.test.context.junit4.SpringRunner;importjava.util.HashMap;importjava.util.List;importjava.util.Map;@RunWith(SpringRunner.class)@SpringBootTest(webEnvironment=SpringBootTest.WebEnvironment.RANDOM_PORT,classes=Starter.class)publicclassMapperProxyFactoryTest{@AutowiredprivateSqlSessionFactorysqlSessionFactory;@Testpublicvoidtest_MapperProxyFactory(){MapperProxyFactory<TestMapper>factory=newMapperProxyFactory<>(TestMapper.class);Map<String,String>xmlMap=newHashMap<>();// 模拟 SqlSessionTestMapperuserDao=factory.newInstance(sqlSessionFactory.openSession());List<UserInfo>list=userDao.getUserList();System.out.println(list);}}

二是模拟代理类，自定义SQL操作，绕开SqlSession

MapperProxy.javapackagecom.hk.mybatis;importorg.apache.ibatis.session.SqlSession;importjava.io.Serializable;importjava.lang.reflect.InvocationHandler;importjava.lang.reflect.Method;importjava.sql.*;importjava.util.ArrayList;importjava.util.HashMap;importjava.util.List;importjava.util.Map;publicclassMapperProxy<T>implementsInvocationHandler,Serializable{privatestaticfinallongserialVersionUID=-6424540398559729838L;privateSqlSessionsqlSession;privatefinalClass<T>mapperInterface;privateMap<String,String>xmlMap;publicMapperProxy(SqlSessionsqlSession,Class<T>mapperInterface,Map<String,String>xmlMap){this.sqlSession=sqlSession;this.mapperInterface=mapperInterface;this.xmlMap=xmlMap;}@OverridepublicObjectinvoke(Objectproxy,Methodmethod,Object[]args)throwsThrowable{if(Object.class.equals(method.getDeclaringClass())){// Object 提供的toString、hashCode等不需要代理执行returnmethod.invoke(this,args);}else{Stringsql=xmlMap.get(method.getName());returnexecuteSql(sqlSession.getConnection(),sql);//return sqlSession.selectList(method.getName(), args); // 代理映射最终执行是 SqlSession}}publicObjectexecuteSql(Connectionconn,Stringsql)throwsThrowable{Listrtn=newArrayList();Statementstat=conn.createStatement();ResultSetrs=stat.executeQuery(sql);ResultSetMetaDatarsmd=rs.getMetaData();intcols=rsmd.getColumnCount();while(rs.next()){Mapm=newHashMap();for(inti=1;i<=cols;i++){StringcolName=rsmd.getColumnName(i);StringcolVal=rs.getString(colName);m.put(colName,colVal);}rtn.add(m);}returnrtn.toArray();}}MapperProxyFactory.javapackagecom.hk.mybatis;importorg.apache.ibatis.session.SqlSession;importjava.lang.reflect.Proxy;importjava.util.Map;publicclassMapperProxyFactory<T>{privatefinalClass<T>mapperInterface;publicMapperProxyFactory(Class<T>mapperInterface){this.mapperInterface=mapperInterface;}publicTnewInstance(SqlSessionsqlSession,Map<String,String>xmlMap){finalMapperProxy<T>mapperProxy=newMapperProxy<>(sqlSession,mapperInterface,xmlMap);// 注意：接口在扫描时通过ClassScanner.scanPackage()加载为了一个Java类return(T)Proxy.newProxyInstance(mapperInterface.getClassLoader(),newClass[]{mapperInterface},mapperProxy);// 传入类加载器、接口的类对象，代理目标类，创建 JDK 动态代理对象}}TestMapper.javapackagecom.hk.mybatis;importcom.baomidou.mybatisplus.core.conditions.Wrapper;importcom.baomidou.mybatisplus.core.mapper.BaseMapper;importcom.baomidou.mybatisplus.core.metadata.IPage;importcom.baomidou.mybatisplus.core.toolkit.Constants;importcom.hk.entity.UserInfo;importorg.apache.ibatis.annotations.Mapper;importorg.apache.ibatis.annotations.Param;importjava.util.List;publicinterfaceTestMapperextendsBaseMapper<UserInfo>{publicObjectgetUserList();publicObjectgetUserByName(@Param("name")Stringname);}MapperProxyFactoryTest.javapackagecom.hk.mybatis;importcom.hk.Starter;importcom.hk.entity.UserInfo;importcom.hk.mapper.UserMapper;importorg.apache.ibatis.session.SqlSessionFactory;importorg.junit.Test;importorg.junit.runner.RunWith;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.boot.test.context.SpringBootTest;importorg.springframework.test.context.junit4.SpringRunner;importjava.util.HashMap;importjava.util.List;importjava.util.Map;@RunWith(SpringRunner.class)@SpringBootTest(webEnvironment=SpringBootTest.WebEnvironment.RANDOM_PORT,classes=Starter.class)publicclassMapperProxyFactoryTest{@AutowiredprivateSqlSessionFactorysqlSessionFactory;@Testpublicvoidtest_MapperProxyFactory(){MapperProxyFactory<TestMapper>factory=newMapperProxyFactory<>(TestMapper.class);Map<String,String>xmlMap=newHashMap<>();// 模拟 SqlSessionxmlMap.put("getUserList","select u.* from user u");xmlMap.put("getUserByLoginId","模拟执行 Mapper.xml 中 SQL 语句的操作：查询用户信息");TestMapperuserDao=factory.newInstance(sqlSessionFactory.openSession(),xmlMap);Objectobj=userDao.getUserList();Object[]userDim=(Object[])obj;for(introw=0;row<userDim.length;row++){Mapmap=(Map)userDim[row];System.out.println(map);}}}