MyBatis笔记-快速使用

MyBatis官方文档：https://mybatis.org/mybatis-3/

完整目录结构如下

1. 创建数据库表

首先创建一个User表，便于之后的测试

建表语句

create database `mybatis`;

use `mybatis`;

create table `user` (
	`id` int(20) not null,
    `name` varchar(30) default null,
    `pwd` varchar(30) default null
)engine = innodb default charset = utf8;

insert into `user`(`id`, `name`, `pwd`) values
(1,'a','123456'),
(2,'b','123456'),
(3,'c','123456')

user 表中内容

2 导入依赖包

新建一个maven项目，pom.xml中导入相关的包

    org.mybatis
    mybatis
    3.5.10



    mysql
    mysql-connector-java
    8.0.29



    junit
    junit
    4.13.1
    test

3 数据库连接配置

在 mybatis-config.xml 中可以对 MyBatis 进行配置

官方配置文档：https://mybatis.org/mybatis-3/zh/configuration.html

下面是一个数据库连接的配置例子

4 获取 SqlSession 封装

将官网提供的下面三行代码封装成工具类 MyBatisUtils，便于获取 sqlSession 实例

String resource = "org/mybatis/example/mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

public class MyBatisUtils {
    private static final SqlSessionFactory sqlSessionFactory;

    static {
        String resource = "org/mybatis/example/mybatis-config.xml";
        InputStream inputStream = null;
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        try {
            inputStream = Resources.getResourceAsStream(resource);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
}

5 编写实体类和接口

实体类 User

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

    // 省略 getter 和 setter 方法

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

UserMapper 接口

public interface UserMapper {
    List getUserList();
}

6 XML 定义 SQL 映射

userMapper.xml

    
        select * from user
    

7 Mapper 注册

mybatis-config.xml

8 Maven 资源过滤配置

maven 项目默认资源是在 resources 目录下

如果目标资源文件在其他目录下，比如userMapper 就在 src/main/java目录下，需要在配置 resources，

pom.xml

    
        
            src/main/resources
            
                ***.xml
            
            true
        
        
            src/main/java
            
                ***.xml
            
            true
        
    

9 测试执行 SQL

通过 SqlSession 实例来直接执行已映射的 SQL 语句

方式一

try (SqlSession session = sqlSessionFactory.openSession()) {
  Blog blog = (Blog) session.selectOne("org.mybatis.example.BlogMapper.selectBlog", 101);
}

方式二（推荐）

try (SqlSession session = sqlSessionFactory.openSession()) {
  BlogMapper mapper = session.getMapper(BlogMapper.class);
  Blog blog = mapper.selectBlog(101);
}

注意：确保 SqlSession 在finally代码中或try-resource中被关闭

public class UserMapperTest extends TestCase {
    SqlSession sqlSession = MyBatisUtils.getSqlSession();;
    public void testGetUserList() {
        try {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            List userList = userMapper.getUserList();
            for (User user : userList) {
                System.out.println(user);
            }
        } finally {
          sqlSession.close();
        }
    }
}