Mybatis学习笔记(二)

2024-01-02 19:26:40

一、第一个Mybatis案例

1.搭建数据库环境

CREATE DATABASE `mybatis`;
USE `mybatis`;
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,'Autumn27','123456'),(2,'法外狂徒张三','333333'),(3,'西装暴徒李四','444444')

创建好数据库后，刷新数据库

2.导入Mybatis相关jar包，推荐用Maven进行项目管理

　　Maven仓库：https://mvnrepository.com/

<dependencies>
    <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.7</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.25</version>
    </dependency>
　　　　<!-- https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-api -->
　　　　<dependency>
　　　　　　<groupId>org.junit.jupiter</groupId>
　　　　　　<artifactId>junit-jupiter-api</artifactId>
　　　　　　<version>5.8.0-M1</version>
　　　　　　<scope>test</scope>
　　　　</dependency>

</dependencies>

　　相关jar包：　

mybatis需要jar包：mybatis-3.5.7.jar(必备)
mysql驱动jar包：mysql-connector-java-8.0.25.jar(必备)
JUnit jar包：junit-jupiter-api-5.8.0-M1.jar(推荐，用于测试代码)

3.编写mybatis核心配置文件

　　MyBatis 的xml配置文件（configuration XML）中包含了对 MyBatis 系统的核心设置，包含获取数据库连接实例的数据源（DataSource）和决定事务作用域和控制方式的事务管理器（TransactionManager）

　　编写配置文件mybatis-config.xml

<?xml version="1.0" encoding="UTF8" ?>
<!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="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/autumn/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

4.编写工具类文件 MybatisUtils.java

//工具类 sqlSessionFactory 生产 sqlSession
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();
        }
    }

    //获取sqlSessionFactory生产的 sqlSession对象
    //sqlSession包含了面向数据库执行的 所有SQL语句 所需的方法
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();

    }
}

5.创建实体类及其对应Mapper接口

　　实体类User.java

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

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

　　UserMapper.java

public interface UserMapper {
    //查询所有用户
    List<User> getUserList();
}

6.编写UserMapper.xml，xml文件中存放对应的Sql语句

<?xml version="1.0" encoding="UTF8"?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.autumn.mapper.UserMapper">

    <!-- id 等价于 重写接口的方法名 -->
    <!-- select标签 内写 sql语句 -->
    <!-- 查询所有用户 -->
    <select id="getUserList" resultType="com.autumn.pojo.User">
        select *
        from mybatis.user;
    </select>

</mapper>

　　其中 <mapper namespace="com.autumn.mapper.UserMapper"> 用来绑定xml对应的Mapper接口

　　有关select相关语句在Mybatis中文文档下的XML 映射器文件有说明。

7.编写测试文件UserMapperTest.java

　　查询所有用户

@Test
    public void testGetUserList(){

        //获取sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        try{
            //执行
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            List<User> userList = userMapper.getUserList();

            for (User user : userList) {
                System.out.println(user);
            }

        }finally {
            //关闭sqlSession
            sqlSession.close();
        }
    }

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