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

Posted 2021-12-07 CodeJiao

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

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>smm_heima</artifactId>
        <groupId>com.tian</groupId>
        <version>1.0-SNAPSHOT</version>
        <relativePath>../../pom.xml</relativePath>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>mybatis_01</artifactId>
    <dependencies>
        <!--        mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.25</version>
        </dependency>
        <!--        mybatis依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.6</version>
        </dependency>
        <!--        单元测试-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
        </dependency>
        <!--        日志打印-->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
    </dependencies>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

</project>

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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

<?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="userMapper">
    <!--查询操作-->
    <select id="findAll" resultType="com.tian.pojo.User">
        select *
        from user
    </select>
</mapper>

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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

<?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>

    <!--通过properties标签加载外部properties文件-->
    <properties resource="jdbc.properties"/>

    <!--数据源环境-->
    <environments default="developement">
        <environment id="developement">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    <!--加载映射文件-->
    <mappers>
        <mapper resource="com.tian.mapper/UserMapper.xml"/>
    </mappers>
</configuration>

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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;

/**
 * ClassName: UserDao
 * Description: 查询所有用户
 *
 * @author Tianjiao
 * @date 2021/11/5 19:19
 */
public interface UserDao {
    List<User> 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;

/**
 * ClassName: UserDaoImpl
 * Description:
 *
 * @author Tianjiao
 * @date 2021/11/5 19:20
 */
public class UserDaoImpl implements UserDao {
    @Override
    public List<User> 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<User> 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
   

<?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">
<!--现在的namespace对应UserDao的全限定类名-->
<mapper namespace="com.tian.dao.UserDao">

    <!--查询操作 id对象UserDao的方法名-->
    <select id="findAll" resultType="com.tian.pojo.User">
        select *
        from user
    </select>
</mapper>

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<User> 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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