SpringBoot 从入门到入门（九 ORM-MyBatis）

一.增加 dependency

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.4</version>
        </dependency>

二.增加配置文件

在resources文件夹中新增 mybatis-config.xml 用以存放MyBatis配置

<?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="properties.yml"/>
    <environments default="mysql">
        <environment id="mysql">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="UserMapper.xml"/>
    </mappers>
</configuration>

其中，properties.yml同样位于resources文件夹中 存放的是一些数据库配置信息，也可以存放其他配置

driver: com.mysql.cj.jdbc.Driver
url: jdbc:mysql://127.0.0.1:3306/test
username: root
password: 123456

UserMapper.xml同样位于resources文件夹中，存放具体的查询信息，id为调用标识，resultType为返回数据类型

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.demo.mapper.UserMapper">
    <select id="getUser" resultType="com.example.demo.entity.UserEntity">
        select * from user
    </select>
</mapper>

三.创建路由并访问

    @RequestMapping("/users")
    public List<UserEntity> users() throws IOException {
        // mybatis-config.xml 为第二步中创建的文件
        String resource = "mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(in);
        SqlSession sqlSession = sessionFactory.openSession(true);
        // getUser 为UserMapper.xml中定义好的查询id
        return sqlSession.selectList("getUser");
    }

四.带有参数的查询

编辑 UserMapper.xml，增加如下查询

<select id="getOneUser" resultType="com.example.demo.entity.User">
        select * from user where id = #{id}
</select>

创建路由并访问

@RequestMapping("/user")
    public UserEntityuser(int id) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(in);
        SqlSession sqlSession = sessionFactory.openSession(true);
        return sqlSession.selectOne("getOneUser",id);
    }

五.如上方式在调用时，不够清晰明了，可以用另外一种方式调用

com.example.demo下创建mapper package，并创建UserMapper

package com.example.demo.mapper;

import com.example.demo.entity.UserEntity;
import org.apache.ibatis.annotations.Param;

import java.util.List;

public interface UserMapper {
    List<UserEntity> getUser();
    UserEntity getOneUser(@Param("id") int id);
}

创建路由并访问

    @RequestMapping("/users1")
    public List<UserEntity> users1() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(in);
        SqlSession sqlSession = sessionFactory.openSession(true);
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        return mapper.getUser();
    }

    @RequestMapping("/user1")
    public UserEntityuser1(int id) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(in);
        SqlSession sqlSession = sessionFactory.openSession(true);
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        return mapper.getOneUser(id);
    }

六.除了之上mapper的引入方式，还有其他的引入方式

https://www.cnblogs.com/my-ordinary/p/13503085.html