MyBatis框架入门：CRUD操作详解-优快云博客

1 Mybatis是什么

MyBatis 是一款优秀的持久层框架，它支持自定义 SQL、存储过程以及高级映射。MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。

2 CRUD

2.1 准备工作

项目整体架构如下图

2.1.1 准备数据库（表）

#创建数据库
create database `mybatis`;

#切换数据库
use mybatis;

#创建表
create table user( 
`id` bigint not null primary key, 
`name` varchar(30) default null, 
`pwd` varchar(30) default null
)ENGINE=innodb default charset=utf8;

#插入数据
insert into `user` (`id`, `name`, `pwd`) values 
(1, 'Jason', '123456'),
(2, 'john', '123456'),
(3, 'leo', '123456');

2.1.2 配置文件

1、jdbc.properties文件

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone=GMT
jdbc.username=root
jdbc.password=xxxx

2、mybatis-config.xml文件

<?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>
    <properties resource="jdbc.properties"></properties>

    <environments default="development">
        <environment id="development">
            <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>

    <!--每一个Mapper.xml都需要在此注册-->
    <mappers>
        <mapper resource="com/jason/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

2.1.3 工具类

编写工具类用以获取SqlSession，以下代码为MybatisUtils的内容

package com.jason.utils;

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 MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            //获取SqlSessionFactory对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }

}

2.1.3 pojo类

创建User类，与数据库形成映射关系

package com.jason.pojo;

public class User {
    private long id;
    private String name;
    private String pwd;

    public User() {
    }

    public User(long id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

2.2 mapper类

编写mapper类（相当于jdbc中的DAO接口），实现crud（增删改查），UserMapper类代码如下：

package com.jason.mapper;

import com.jason.pojo.User;

import java.util.List;

public interface UserMapper {
    List<User> getUserList();

    User getUserById(long id);

    int addUser(User user);

    int updateUser(User user);

    int deleteUser(User user);
}

2.3 mapper对应xml文件

编写mapper对应xml文件（相当于jdbc中DAO的实现类），用xml配置文件替代代码，具体如下：

<?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">
<!--namespace绑定一个对应的Mapper（Dao）接口-->
<mapper namespace="com.jason.mapper.UserMapper">

    <!--select查询语句-->
    <select id="getUserList" resultType="com.jason.pojo.User">
        select *
        from mybatis.user
    </select>

    <select id="getUserById" parameterType="long" resultType="com.jason.pojo.User">
        select *
        from mybatis.user
        where id = #{id}
    </select>

    <!--新增用户-->
    <insert id="addUser" parameterType="com.jason.pojo.User">
        insert into user (id, name, pwd)
        values (#{id}, #{name}, #{pwd})
    </insert>

    <update id="updateUser" parameterType="com.jason.pojo.User">
        update user
        set pwd  = #{pwd},
            name = #{name}
        where id = #{id};
    </update>

    <delete id="deleteUser" parameterType="com.jason.pojo.User">
        delete
        from user
        where id = #{id}
          and name = #{name}
          and pwd = #{pwd};
    </delete>

</mapper>

切记在mybatis-config.xml中注册mapper的XML文件

<!--每一个Mapper.xml都需要在此注册-->
    <mappers>
        <mapper resource="com/jason/mapper/UserMapper.xml"/>
    </mappers>

2.4 测试

注意测试类（尽量）和main包下的路径保持一致，UserMapperTest代码如下：

package com.jason.mapper;

import com.jason.pojo.User;
import com.jason.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserMapperTest {
    @Test
    public void getUserListTest() {
        //第一步：获取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        //第二步：getMapper
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = userMapper.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }

        //第三步：关闭SqlSession
        sqlSession.close();
    }

    @Test
    public void getUserByIdTest() {
        //第一步：获取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        //第二步：getMapper
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.getUserById(4);
        System.out.println(user);
        //第三步：关闭SqlSession
        sqlSession.close();
    }

    // 增删改需要提交事务
    @Test
    public void addUserTest() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = new User(4, "Mary", "123");
        int res = mapper.addUser(user);
        System.out.println("影响行数：" + res);

        //提交事务
        sqlSession.commit();

        sqlSession.close();
    }

    @Test
    public void updateUserTest() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        int res = mapper.updateUser(new User(4, "Lisa", "123456"));
        System.out.println("影响行数：" + res);

        //提交事务
        sqlSession.commit();

        sqlSession.close();

    }

    @Test
    public void deleteUserTest() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        int res = mapper.deleteUser(new User(4, "Mary", "123"));
        System.out.println("影响行数：" + res);

        sqlSession.commit();

        sqlSession.close();
    }

}

注意，增删改的时候需要commit，否则操作不生效！！！