Mybatis -- MyBatis的Dao层实现（传统方式实现、接口代理方式实现）

预备：准备工作

准备工作 创建一个maven工程：

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1.1 添加Mybatis坐标（导入相关的依赖）

pom.xml

    
        smm_heima
        com.tian
        1.0-SNAPSHOT
        ../../pom.xml
    
    4.0.0

    mybatis_01
    
        
        
            mysql
            mysql-connector-java
            8.0.25
        
        
        
            org.mybatis
            mybatis
            3.4.6
        
        
        
            junit
            junit
            4.13.2
        
        
        
            log4j
            log4j
            1.2.17
        
    

    
        8
        8
    

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1.2 创建User数据表（搭建数据库环境）

执行下列sql语句

CREATE DATAbase `test`;
USE `test`;
CREATE TABLE `user` ( 
 `id` INT NOT NULL PRIMARY KEY, 
 `username` VARCHAR ( 30 ) DEFAULT NULL, 
 `password` VARCHAR ( 30 ) DEFAULT NULL 
 ) ENGINE = INNODB DEFAULT CHARSET = utf8;
 
 INSERT INTO USER (`id`, `username`, `password`) VALUES
 (1,'thylove', '123456'), 
 (2, 'root', '123456'), 
 (3, 'admin', '123456');

执行结果：

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1.3 编写User实体类

User.java

package com.tian.pojo;

public class User {
    private int id;
    private String username;
    private String password;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + ''' +
                ", password='" + password + ''' +
                '}';
    }
}

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1.4 编写映射文件UserMapper.xml

UserMapper.xml

    
    
        select *
        from user
    

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1.5 编写核心文件SqIMapConfig.xml

准备工作：编写数据库配置文件：

jdbc.properties

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/test
jdbc.username=root
jdbc.password=317525

正式开始：

SqIMapConfig.xml

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1. 传统方式实现

UserDao.java

package com.tian.dao;

import com.tian.pojo.User;

import java.util.List;


public interface UserDao {
    List findAll() throws Exception;
}

UserDaoImpl.java

package com.tian.dao.impl;

import com.tian.dao.UserDao;
import com.tian.pojo.User;
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.InputStream;
import java.util.List;


public class UserDaoImpl implements UserDao {
    @Override
    public List findAll() throws Exception {
        //获得核心配置文件
        InputStream resourceAsStream = Resources.getResourceAsStream("SqIMapConfig.xml");
        //获得session工厂对象
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        //获得session回话对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //执行操作  参数：namespace+id
        List userList = sqlSession.selectList("userMapper.findAll");
        //释放资源
        sqlSession.close();
        return userList;
    }
}

测试代码:

MyBatisTest.java

package com.tian.test;

import com.tian.dao.impl.UserDaoImpl;
import org.junit.Test;

public class MyBatisTest {

    @Test
    //查询操作
    public void test1() throws Exception {
        System.out.println(new UserDaoImpl().findAll());
    }
}

运行结果：

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2. 接口代理方式实现（常用）

说明：

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实例：

1. 我们先删除dao层的impl的包
   

2. 修改UserMapper.xml
   

    
    
        select *
        from user
    

3. 测试：
   
   MyBatisTest.java

package com.tian.test;

import com.tian.dao.UserDao;
import com.tian.pojo.User;
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 org.junit.Test;

import java.io.InputStream;
import java.util.List;

public class MyBatisTest {

    @Test
    //查询操作
    public void test1() throws Exception {
        // 获取SqlSession
        InputStream resourceAsStream = Resources.getResourceAsStream("SqIMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        // 调用dao层方法
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        List userList = mapper.findAll();
        System.out.println(userList);
    }
}

运行结果：

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3. 比较2种方式

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