MyBatis第一个程序

思路

搭建环境 --> 导入MyBatis --> 编写代码 --> 测试

代码演示

环境说明：

• JDK 8
• MySQL 5.7.19
• maven-3.6.0
• IDEA

1. 创建数据库并插入数据

CREATE DATABASE `mybatis`;

USE `mybatis`;

DROP TABLE IF EXISTS `user` (
    `id` int(10) AUTO_INCREMENT PRIMARY KEY,
    `name` varchar(30) DEFAULT NULL,
    `pwd` varchar(30) DEFAULT NULL
) ENGIN=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO `user` (`name`,`pwd`) values ("linux","linux123") ("windows","windows123","macos","macos123");

2. 导入MyBatis相关jar包

可以去Maven Respository去搜索相关jar包。

    org.mybatis
    mybatis
    3.5.4




    mysql
    mysql-connector-java
    8.0.19

3. 编写配置文件

4. 编写MyBatis工具类

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;

public class MyBatisUtils {
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //获取SqlSession连接
    public static SqlSession getSession() {
        return sqlSessionFactory.openSession();
    }
}

5. 创建实体类

public class User {
    private int id;
    private String name;
    private String pwd;
    
    //有参构造器
    //无参构造器
    //set方法
    //get方法
    //toString重写
}

上面注释的部分自己写，或使用IDEA就能生成，在编辑区快捷键Alt + Insert，toString要重写，不然第8步打印会输出该对象的引用，格式为包名.类名.@八位字符。

6. 编写Mapper接口类

import com.geek.pojo.User;
import java.util.List;

public interface UserMapper {
    List selectUser();
}

7. 编写Mapper.xml配置文件

注意：namespace不要写错，否则会报错

  
    select * from user
  

8. 编写测试类

Junit包测试

public class MyTest {
    @Test
    public void selectUser() {
        SqlSession session = MybatisUtils.getSession();
        //方法一:
        //List users = session.selectList("com.geek.mapper.UserMapper.selectUser");
        //方法二:
        UserMapper mapper = session.getMapper(UserMapper.class);
        List users = mapper.selectUser();

        for (User user: users){
            System.out.println(user);
        }
        session.close();
    }
}

9. 运行测试

可能出现的问题

Maven静态资源过滤问题

    
        src/main/java
        
            **/*.properties
            **/*.xml
        
        false
    
    
        src/main/resources
        
            **/*.properties
            **/*.xml
        
        false
    

第7步Mapper.xml中命名空间写错，可能会报类似这样的错误

Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException:
### Error updating database. Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for xxdfly.mapping.userMaper.updateUser
### Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for xxdfly.mapping.userMaper.updateUser
at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:26)
at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:154)
at test.MybatisTest.main(MybatisTest.java:37)
Caused by: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for xxdfly.mapping.userMaper.updateUser