Mybatis框架之代理模式(Proxy Pattern)的实现

UserMapper (接口)
    ↓
SqlSession.getMapper(UserMapper.class)
    ↓
MapperProxy (JDK 动态代理)
    ↓
MappedStatement (映射 SQL)
    ↓
执行 SQL 并返回结果

package com.example.mapper;

import com.example.model.User;
import java.util.List;

public interface UserMapper {
    // 查询所有用户
    List<User> getAllUsers();

    // 根据 ID 查询用户
    User getUserById(int id);
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.mapper.UserMapper">
    <select id="getAllUsers" resultType="com.example.model.User">
        SELECT * FROM users;
    </select>

    <select id="getUserById" parameterType="int" resultType="com.example.model.User">
        SELECT * FROM users WHERE id = #{id};
    </select>
</mapper>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
    PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mydatabase"/>
                <property name="username" value="root"/>
                <property name="password" value="password"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/example/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import com.example.mapper.UserMapper;
import com.example.model.User;
import java.io.InputStream;
import java.util.List;

public class MyBatisExample {
    public static void main(String[] args) {
        String resource = "mybatis-config.xml";
        try (InputStream inputStream = Resources.getResourceAsStream(resource)) {
            // 创建 SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

            // 打开 SqlSession
            try (SqlSession session = sqlSessionFactory.openSession()) {
                // 获取 Mapper 接口的代理对象
                UserMapper userMapper = session.getMapper(UserMapper.class);

                // 调用代理对象的方法
                List<User> users = userMapper.getAllUsers();
                users.forEach(user -> System.out.println(user.getName()));

                // 根据 ID 查询用户
                User user = userMapper.getUserById(1);
                System.out.println("User ID 1: " + user.getName());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public class MapperProxy implements InvocationHandler {
    private SqlSession sqlSession;
    private Class<?> mapperInterface;

    public MapperProxy(SqlSession sqlSession, Class<?> mapperInterface) {
        this.sqlSession = sqlSession;
        this.mapperInterface = mapperInterface;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        String statementId = mapperInterface.getName() + "." + method.getName();
        return sqlSession.selectList(statementId, args);
    }
}