第一个MyBatis程序

第一个MyBatis程序

思路：搭建环境->导入MyBatis->编写代码->测试

搭建数据库

CREATE DATABASE `mybatis`;
USE `mybatis`;

CREATE TABLE `user` (
	`id` INT ( 20 ) NOT NULL,
	`name` VARCHAR ( 30 ) DEFAULT NULL,
	`pwd` VARCHAR ( 200 ) DEFAULT NULL,
PRIMARY KEY (id) 
)ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT INTO `user`(`id`, `name`, `pwd`) VALUES (1,'张三','123456'),(2,'李四','123456'), (3,'王五','123456');

新建项目

1.新建一个普通的maven项目
2.删除src目录
3.导入Maven依赖

<!--导入依赖-->
    <dependencies>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</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>

创建一个模块

• 编写mybatis的核心配置文件

<?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">
<!--核心配置文件-->
<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=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/mybatis/example/BlogMapper.xml"/>
    </mappers>
</configuration>

• 编写mybatis的工具类

//sqlSessionFactory -->sqlSession
public class MybatisUtil {
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            //使用Mybatis的第一步，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();
        }
    }

    //既然有了SqlSecessionFactory， 顾名思义，我们就可以从中获得SqlSession的实例了。
    //SqlSession完全包含了面向数据库执行的Sql命令所需的所有方法。
    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }

}

编写代码

• 实体类

package com.ultraBlast.pojo;

/**
 * @Auther: UltraBlast
 * @Date : 2021/2/26 - 02 - 26 - 2021 - 18:08
 * @Description : com.ultraBlast.pojo
 * @version: 1.0
 */
public class user {
    private int id;
    private String name;
    private String pwd;

    public user(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public user() {
    }

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

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

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public String getPwd() {
        return pwd;
    }
}

• 实现类（Dao接口）

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

• 接口实现类（由原来的UserDaoImpl转换为一个mapper配置文件）

<?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">
<!--namespace=绑定一个对应的DAO/MAPPER接口-->
<mapper namespace="com.ultraBlast.dao.UserDao">
    <select id="getUserList" resultType="com.ultraBlast.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

测试

注意点：org.apache.ibatis.binding.BindingException: Type interface com.ultraBlast.dao.UserMapper is not known to the MapperRegistry.
MapperRegistry是什么？
核心配置文件中注册mappers

• 使用JUnit测试

    @Test
    public void test() {
        //获取sqlsession对象
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        //执行sql
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = userMapper.getUserList();

        for (User user : userList) {
            System.out.println(user.toString());
        }
        //关闭sqlsession
        sqlSession.close();
    }

可能会遇到的问题
1.配置文件没有注册
2.绑定接口错误
3.方法名不对
4.返回类型不对
5.Maven导出资源问题