mybatis3--link

第一步maven项目：配置jar包

<?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">
    <modelVersion>4.0.0</modelVersion>
    <!--父工程-->
    <groupId>com.xuwen</groupId>
    <artifactId>Mybatis</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>mybatis-01</module>
    </modules>


    <dependencies>
        <!--mysql-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <!--junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
    </dependencies>


</project>

第二步：Mybatis核心配置文件

2.1编写mybatis的核心配置文件
新建，resources--新建mybatis-config.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>
  <environments default="development">
    <environment id="development">
      <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}"/>
               <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://rm-uf6t9m0yx22dxrya5no.mysql.rds.aliyuncs.com:3306/koa2weibo?serverTimezone=Asia/Shanghai&amp;useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF8&amp;"/>
                <property name="username" value="koa2weibo"/>
                <property name="password" value="passMYblog123"/>
      </dataSource>
    </environment>
  </environments>
    <!--每一个Mapper.xml都需要在Mybatis核心配置文件中注册！！！-->
    <mappers>
        <mapper resource="com/xuwen/dao/UserMapper.xml"/>
    </mappers>
</configuration>

2.2编写mybatis工具类

固定写法，是个套路。

package com.xuwen.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;

/**
 * author:xuwen
 * Created on 2021/7/20
 */
//工具类
    //sqlSessionFactory
public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;

    //静态代码块，初始化就加载
    static{
        InputStream inputStream = null;
        try {
            //第一步：获取sqlSessionFacotry对象
            //官网三句话是套路
            String resource = "mybatis-config.xml";
            inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //获取sqlsession完全包含了，面向数据库执行SQL命令的所有方法
    public static SqlSession getSqlSession(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession;
    }


}

编写代码：

实体类（POJO）-->Dao接口/Mapper（interface）-->接口实现类

实体类，private，无参构造，带参构造，getter/setter

注解注入/xml配置

实体类

package com.xuwen.pojo;

/**
 * author:xuwen
 * Created on 2021/7/21
 */
public class User {
    private int id;
    private String name;
    private String pwd;
    //无参构造
    public User(){}
    //带参构造
    public User(int id, String name,String pwd){
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    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;
    }

    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 + '\'' +
                '}';
    }
}

Dao接口Mapper

package com.xuwen.dao;
import com.xuwen.pojo.User;
import java.util.List;

/**
 * author:xuwen
 * Created on 2021/7/21
 */
public interface UserDao {
    List<User> getUserList();

}

接口实现类

<?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">
<!--Mybatis3官网案例-->
<!--namespace="绑定一个对应的DAO/Mapper接口的类"-->
<!--xml绑定DAO/Mapper接口-->
<mapper namespace="com.xuwen.dao.UserDao">
    <!--select查询-->
    <!--id="DAO包中类，对应方法名"-->
    <!--resultType="pojo包里面对应的类"-->
    <select id="getUserList" resultType="com.xuwen.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

测试代码：

package com.xuwen.dao;

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

import java.util.List;

/**
 * author:xuwen
 * Created on 2021/7/21
 */
public class UserDaoTest {
    @Test
    public void test(){
        //第一步：获得SqlSession对象
       SqlSession sqlSession = MybatisUtils.getSqlSession();
       //第二步：执行sql
        //方法一：getMapper，为了拿到里面的方法
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }

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

    }

}