[Java知识库]Mybatis学习笔记01

目录

1.创建数据库

2.导入Mybatis的依赖

3.Mybatis核心配置文件

4.创建Mybatis工具类

5、创建实体类

6、编写Mapper接口类

7、编写Mapper.xml配置文件

8、编写测试类

1.数据库创建

CREATE DATABASE `mybatis`;

USE `mybatis`;
DROP TABLE IF EXISTS `user`;

CREATE TABLE `user` (
`id` INT(20) NOT NULL,
`name` VARCHAR(30) DEFAULT NULL,
`pwd` VARCHAR(30) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT  INTO `user`(`id`,`name`,`pwd`) VALUES (1,'chen','sdgasjkdg'),(2,'wang','888888'),(3,'li','5645645');

2.导入依赖

<?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>

    <groupId>org.example</groupId>
    <artifactId>com.chang.Mybatis</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>mybatis-01</module>
    </modules>

    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
    </dependencies>


</project>

3.核心配置文件

<?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">
<!--core configuration file-->
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=utf8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

</configuration>

4.工具类

//工具类的目的： 将资源加载进来 并且创建一个可以执行sql的对象(sqlsession)

package com.chang.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;
//工具类的目的： 将资源加载进来 并且创建一个可以执行sql的对象(sqlsession)
public class MybatisUtils {
//提升sqlsessionFactory的作用域
    private static SqlSessionFactory sqlSessionFactory;
//使用Mybatis先要构建工具类 :从 XML 中构建 SqlSessionFactory

    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    //有了SqlSessionFactory 就要获取sqlsession
    //获取SqlSession连接  sqlsession就是操作数据库的对象了，里面有很多操作数据库的方法
    public static SqlSession getSession(){
        return sqlSessionFactory.openSession();
    }

}

5.实体类

package com.chang.pojo;

public class User {
    private int id;  //id
    private String name;   //姓名
    private String pwd;   //密码

    public User() {
    }

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

6.Mapper接口

Mapper接口相当于Userdao接口

package com.chang.dao;

import com.chang.pojo.User;

import java.util.List;

public interface UserDao {
    List<User> getUserList();
}

7.Mapper.xml文件

相当于是Mapper接口的实现类

<?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">
<!--这个xml文件就相当于dao接口的实现类-->
<!--namespace绑定一个对应的dao\mapper接口-->
<mapper namespace="com.chang.dao.UserDao">
<!--相当于实现了UserDao接口-->
<!--    “<” 符号下有提示很多种sql方法 这里用选择（select）语句来举例-->
    <select id="selectUser" resultType="com.chang.pojo.User">
  select * from user
 </select>
</mapper>

注意命名空间Namespace是Mapper(UserDao）接中的方法名

结果类型 resultType是实体类User? 也就是说对应数据库中的一张User表。

8.测试类

package com.chang.dao;

import com.chang.pojo.User;
import com.chang.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.graalvm.compiler.lir.LIRInstruction;
import org.junit.Test;

import java.util.List;

public class UserDaoTest {
    @Test
    public void test(){
        //测试类第一步：获得sqlsession对象 通过刚才创建的MybatisUtils的工具类中的getSession()方法获得sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSession();
        //第二步 通过反射机制获得接口UserDao接口中的方法 执行sql
        //方法一 getMapper
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();
        for (User user: userList){
            System.out.println(user);
        }
        sqlSession.close();
    }
}