mybatis配置和使用

1，配置

MyBatis实现映射器的2种方式：XML文件形式和注解形式，下文主要是用xml形式，比较好维护

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">
<!-- 填写自己的mysql用户名和密码， 还有连接的url要加上"?serverTimezone=GMT%2B8"不然会报错 -->
<configuration>
    <!--环境的配置...  -->
    <properties resource="jdbc-prod.properties"/>
    <settings>
        <!--其他配置...  -->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
        <!--其他配置...  -->
    </settings>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver" />
                <property name="url" value="${database.url}" />
                <property name="username" value="${database.username}" />
                <property name="password" value="${database.password}" />
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="mapper/ActionMapper.xml"/>
        <mapper resource="mapper/OperatorMapper.xml"/>
    </mappers>
</configuration>

jdbc-dev.properties文件：

database.url=jdbc:mysql://localhost:3306/demo?serverTimezone=GMT%2B8
database.username=root
database.password=

2，使用

新建数据表

新建实体：

package com.hanlin.bean;

import java.util.List;

public class User {

    private int id;

    private String name;

    private String address;

    private List<Computer> computerList;

    public int getId() {
        return id;
    }

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

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getName() {
        return name;
    }

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

    public List<Computer> getComputerList() {
        return computerList;
    }

    public void setComputerList(List<Computer> computerList) {
        this.computerList = computerList;
    }

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

package com.hanlin.bean;

public class Computer {
    private int id;
    private String name;

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

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

ComputerMapper文件：

package com.hanlin.mapper;

import com.hanlin.bean.Computer;
import com.hanlin.bean.User;

import java.util.List;

public interface ComputerMapper {

    List<User> getList();

}

computer.xml文件

<?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="com.hanlin.mapper.ComputerMapper">
    <resultMap id="UserMap" type="com.hanlin.bean.User">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="address" column="address"/>
        <collection property="computerList" ofType="com.hanlin.bean.Computer">
            <id property="id" column="computer_id"/> //这个id要自己另外起别名
            <result property="name" column="computer_name"/>
        </collection>
    </resultMap>

    <select id="getList" resultMap="UserMap">
        select u.*,c.`name`as computer_name from computer as c RIGHT JOIN user as u on u.id = c.user_id;
    </select>

</mapper>

SqlSessionFactoryUtil文件：

package com.hanlin.util;

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;
import java.io.Reader;

public class SqlSessionFactoryUtil {
    private static final String resource = "mybatis-cfg.xml";

    public static SqlSession getSqlSession() throws IOException {
        //获取配置的资源文件
        Reader reader = Resources.getResourceAsReader(resource);
        //得到SqlSessionFactory，使用类加载器加载xml文件
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader);
        //得到sqlsession对象，这个对象就能执行配置文件中的sql语句啦
        SqlSession session = factory.openSession();

        return session;
    }
}

UserTest文件：

public class UserTest {

    public static void main(String[] args) throws Exception{
        SqlSession session = SqlSessionFactoryUtil.getSqlSession();
        System.out.println("********************************************");

        ComputerMapper computerMapper = session.getMapper(ComputerMapper.class);
        List<User> userList = computerMapper.getList();
        for (User user:userList){
            System.out.println(user.toString());
        }
    }
}

运行结果