Mybatis初体验

内容介绍

本文通过一个demo演示Mybatis是如何使用的，不涉及与spring集成相关。本文使用mysql进行演示

本文demo地址：

https://github.com/wheijxiaotbai/HXB_Knowledge.git
分支：hxb_demo_mybatis_01

环境准备

依赖包的导入

在demo中使用的是gradle ，直接在gradle配置文件中加入以下依赖即可

// https://mvnrepository.com/artifact/org.mybatis/mybatis
compile group: 'org.mybatis', name: 'mybatis', version: '3.5.0'

// https://mvnrepository.com/artifact/mysql/mysql-connector-java
compile group: 'mysql', name: 'mysql-connector-java', version: '8.0.15'

mysql环境的准备，表的创建

在具有docker的linux环境下执行
```
docker run -dit --name demo_mysql -p 3306:3306 -e MYSQL_ROOT_PASSWORD=123456 mysql
```
这样，就能快速启动一个mysql容器，账户为root，密码为123456，当然你可以自己修改MYSQL_ROOT_PASSWORD=123456参数以修改密码

执行下面sql语句创建User表
```
create table user (
      `id` int,
  `name` VARCHAR(32),
  `age` int,
  PRIMARY KEY (`id`)
) 
```

原生方式

配置mybatis-config.xml

配置数据模型对应的sql.xml（比如User模型对应的User.xml）

创建model类（User）

mybatis-config.xml




    
        
            
            
                //数据库驱动
                
                //配置数据库参数
                
                
                
            
        
    
    
        //User.xml文件

User.xml




//这里将命名空间设置为test

    
    //parameterType为传入参数类型，resultType为输出数据类型，#{value}即为传入的参数
    

    
    
        insert into user (id , name , age)
        values (#{id},#{name},#{age})
    

    
    
        delete from user where id = #{value}
    

    
    
        update user
        set name = #{name} , age = #{age}
        where id = #{id}

User，user类和你刚刚创建的表一致

public class User {

    private int id;
    private String name;
    private int age;

    public User() {}

    private User(Builder builder) {
        setId(builder.id);
        setName(builder.name);
        setAge(builder.age);
    }

    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 int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public static final class Builder {
        private int id;
        private String name;
        private int age;

        public Builder() {
        }

        public Builder id(int val) {
            id = val;
            return this;
        }

        public Builder name(String val) {
            name = val;
            return this;
        }

        public Builder age(int val) {
            age = val;
            return this;
        }

        public User build() {
            return new User(this);
        }
    }
}

接下来进行测试 MybatisTest

import model.User;
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 org.junit.Test;

import java.io.InputStream;

public class MybatisTest {

    /**
     * add user
     * @throws Exception
     */
    @Test
    public void addUserTest() throws Exception {

        //加载核心配置文件
        String resource = "mybatisxml/mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //执行Sql语句
        //通过test.addUser找到user.xml中对于的sql语句，test为user.xml中的命名空间
        sqlSession.insert("test.addUser",
                new User.Builder()
                .id(5)
                .name("张三")
                .age(67)
                .build()
        );
        sqlSession.commit();

    }

    /**
     * find user by id test
     * @throws Exception
     */
    @Test
    public void findUserByIdTest() throws Exception {

        //加载核心配置文件
        String resource = "mybatisxml/mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //执行Sql语句
        User user = sqlSession.selectOne("test.findUserById", 1);
        System.out.println(user.getName());

    }

    /**
     * update user by id
     * @throws Exception
     */
    @Test
    public void updateUserByIdTest() throws Exception {

        //加载核心配置文件
        String reource = "mybatisxml/mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(reource);
        //创建sqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //执行Sql语句
        sqlSession.update("test.updateUserById" ,
                new User.Builder()
                .id(5)
                .name("李四")
                .age(8)
                .build()
        );
        sqlSession.commit();

    }

    @Test
    public void deleteUserByID() throws Exception {

        //加载核心配置文件
        String reource = "mybatisxml/mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(reource);
        //创建sqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //执行sql语句
        sqlSession.delete("test.deleteUserByID" , 5);
        sqlSession.commit();

    }

}

mapper动态代理方式

配置mybatis-config.xml

配置数据模型对应的sql.xml（比如User模型对应的User.xml）

创建model类（User）

mapper映射接口

mapper动态代理方式的mybatis-config.xml，User文件与上一种一致user.xml略有区别

User.xml




//这里的命名空间改为user的mapper映射接口

    
    

    
    
        insert into user (id , name , age)
        values (#{id},#{name},#{age})
    

    
    
        delete from user where id = #{value}
    

    
    
        update user
        set name = #{name} , age = #{age}
        where id = #{id}

UserMapper

public interface UserMapper {

    //遵循四个原则
    //接口 方法名  == User.xml 中 id 名
    //返回值类型  与  Mapper.xml文件中返回值类型要一致
    //方法的入参类型 与Mapper.xml中入参的类型要一致
    //命名空间 绑定此接口
    public User findUserById(int id);

    public void addUser(User user);

    public void updateUserById(User user);

    public void deleteUserByID(int id);

}

接下来进行测试

MybatisMapperTest

import mapper.UserMapper;
import model.User;
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 org.junit.Test;

import java.io.InputStream;

public class MybatisMapperTest {

    /**
     * add user
     * @throws Exception
     */
    @Test
    public void addUserTest() throws Exception {

        //加载核心配置文件
        String resource = "mybatisxml/mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //sqlSession生成实现类
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //调用方法
        userMapper.addUser(
                new User.Builder()
                        .id(5)
                        .name("张三")
                        .age(67)
                        .build()
        );
        sqlSession.commit();

    }

    /**
     * find user by id test
     * @throws Exception
     */
    @Test
    public void findUserByIdTest() throws Exception {

        //加载核心配置文件
        String resource = "mybatisxml/mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //sqlSession生成实现类
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //调用方法
        User user = userMapper.findUserById(1);
        System.out.println(user.getName());

    }

    /**
     * update user by id
     * @throws Exception
     */
    @Test
    public void updateUserByIdTest() throws Exception {

        //加载核心配置文件
        String reource = "mybatisxml/mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(reource);
        //创建sqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //sqlSession生成实现类
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //调用方法
        userMapper.updateUserById(
                new User.Builder()
                        .id(5)
                        .name("李四")
                        .age(8)
                        .build()
        );
        sqlSession.commit();

    }

    @Test
    public void deleteUserByID() throws Exception {

        //加载核心配置文件
        String reource = "mybatisxml/mybatis-config.xml";
        InputStream in = Resources.getResourceAsStream(reource);
        //创建sqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //sqlSession生成实现类
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //调用方法
        userMapper.deleteUserByID(5);
        sqlSession.commit();

    }

}

可能会出现的问题

can not found xxx.xml

这种一般是你的xml文件放的位置不对，或者你写的路径不正确
在mybatis-config.xml中导入失败或者错误，会导致在test的时候空指针异常，应为没有连接上数据库