Mybatis原始碼解析5—— 介面代理

本篇文章，可樂將為大家介紹通過介面代理的方式去執行SQL操作。話不多說，直接上圖：

其實無論哪種方式，我們最終是需要找到對應的 SQL 語句，介面代理的方式就是通過 【包名.方法名】 的方式，去找到 xxxMapper.xml 檔案中的 SQL 語句。

很明顯，通過動態代理的方式，我們能夠實現該功能。下面，可樂將為大家手擼一個 Mybatis 的介面代理。

1、建立介面

package com.itcoke.mapperproxy;

import com.itcoke.bean.Person;

public interface PersonMapper {

    Person selectPersonById(Long pid);

}

2、建立代理類

package com.itcoke.mapperproxy;

import org.apache.ibatis.session.SqlSession;

import java.lang.reflect.InvocationHandler;

import java.lang.reflect.Method;

public class MapperProxyHandler implements InvocationHandler {

    private SqlSession sqlSession;

    private Class<?> targetInterface;

    public MapperProxyHandler(SqlSession sqlSession,Class<?> targetInterface){

        this.sqlSession = sqlSession;

        this.targetInterface = targetInterface;

    }

    @Override

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        String className = targetInterface.getName();

        String methodName = method.getName();

        String statement = className + "." + methodName;

        return sqlSession.selectOne(statement,args[0]);

    }

}

3、建立代理工廠類

package com.itcoke.mapperproxy;

import java.lang.reflect.Proxy;

public class MapperProxyFactory {

    private Class<?> targetInterface;

    public MapperProxyFactory(Class<?> targetInterface){

        this.targetInterface = targetInterface;

    }

    public Object newInstance(MapperProxyHandler handler){

        return Proxy.newProxyInstance(targetInterface.getClassLoader(),

                new Class[]{targetInterface},

                handler);

    }

}

4、建立測試類

package com.itcoke.mapperproxy;

import com.itcoke.bean.Person;

import org.apache.ibatis.io.Resources;

import org.apache.ibatis.session.SqlSession;

import org.apache.ibatis.session.SqlSessionFactory;

import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;

import java.io.InputStream;

public class MapperProxyTest {

    public static void main(String[] args) {

        // 1、獲取目標介面物件

        Class<?> targetInterface = PersonMapper.class;

        // 2、獲取 SqlSession 物件

        SqlSession sqlSession = getSqlSession();

        MapperProxyHandler proxyHandler = new MapperProxyHandler(sqlSession,targetInterface);

        MapperProxyFactory mapperProxyFactory = new MapperProxyFactory(PersonMapper.class);

        PersonMapper personMapper = (PersonMapper)mapperProxyFactory.newInstance(proxyHandler);

        Person person = personMapper.selectPersonById(1L);

        System.out.println(person);

    }

    public static SqlSession getSqlSession() {

        //定義mybatis全域性配置檔案

        String resource = "mybatis-config.xml";

        //載入 mybatis 全域性配置檔案

        InputStream inputStream = null;

        try {

            inputStream = Resources.getResourceAsStream(resource);

        } catch (IOException e) {

            e.printStackTrace();

        }

        //構建sqlSession的工廠

        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        return  sessionFactory.openSession();

    }

}

5、總結

其實 Mybatis 內部實現方式大體上和上面差不多，在加入一些型別處理器，其實就是一個簡易版本的 Mybatis