MyBatis的相应API与传统和代理开发的Dao层实现

短命女 2024-03-30 11:18 77阅读 0赞

## MyBatis的相应API ##

### 1、SqlSession工厂构建器SqlSessionFactoryBuilder ###

常用API：SqlSessionFactory build(InputStream inputStream)

通过加载mybatis的核心文件的输入流的形式构建一个SqlSessionFactory对象

![cc0d24fa3e226c786c7e7b8ea486ab81.png][]

其中，mybatis-config.xml是类加载器的路径，在maven工程下就是resource资源下，Resources工具类，这个类在org.apache.ibatis.io包中。Resource类帮助你从类路径下、文件系统或一个webURL中加载资源文件。

sqkSessionFactory有多个方法创建SqlSession实例，常用的有两个

![852c125f389d9dd576ad95b2dd37a4d5.png][]

### 2、SqlSession会话对象 ###

SqlSession实例在MyBatis是非常强大的一个类，在这里会看到所有执行语句、提交或回滚事务和获取映射实例的方法有

![3cfe9cc35503be7ce68be1a29d7c759c.png][]

操作事务的方法主要有

![294155fd414efe2caef3e302f66eaaea.png][]

## Mybatis的Dao层实现 ##

### 1、传统开发方式-编写UserDao接口 ###

测试编写UserDao接口

> controller包下UserController类下

package com_Dao.controller;
     
    import com_Dao.service.Impl.UserServiceImpl;
    import com_Dao.service.UserService;
    import com_mybatis.pojo.User;
     
    import java.io.IOException;
    import java.util.List;
     
    public class UserController {
        public static void main(String[] args) throws IOException {
            UserService userService=new UserServiceImpl();
            List<User> userList = userService.findAll();
            System.out.println(userList);
        }
     
    }

> service包下UserService下

接口

package com_Dao.service;
     
    import com_mybatis.pojo.User;
     
    import java.io.IOException;
    import java.util.List;
     
    public interface UserService {
     
     public List<User> findAll() throws IOException;
    }

实现类下

package com_Dao.service.Impl;
     
    import com_Dao.Dao.Impl.UserDaoImpl;
    import com_Dao.Dao.UserDao;
    import com_Dao.service.UserService;
    import com_mybatis.pojo.User;
     
    import java.io.IOException;
    import java.util.List;
     
    public class UserServiceImpl implements UserService {
     UserDao userDao=new UserDaoImpl();
        @Override
        public List<User> findAll() throws IOException {
            return userDao.findAll();
        }
    }

> dao包下的UserDao下

接口下

package com_Dao.Dao;
     
    import com_mybatis.pojo.User;
     
    import java.io.IOException;
    import java.util.List;
     
    public interface UserDao {
        public List<User> findAll() throws IOException;
    }

实现类下

package com_Dao.Dao.Impl;
     
    import com_Dao.Dao.UserDao;
    import com_mybatis.pojo.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 java.io.IOException;
    import java.io.InputStream;
    import java.util.List;
     
    public class UserDaoImpl implements UserDao {
        @Override
        public List<User> findAll() throws IOException {
     
            //获得核心配置文件
            InputStream resourceAsFile = Resources.getResourceAsStream("sqlMapConfig.xml");
            //获得session工厂对象
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsFile);
            //获得session会话对象
            SqlSession sqlSession = sqlSessionFactory.openSession();
            //执行操作 参数：namespace+id
            List<User> userList = sqlSession.selectList("userMapper.findAll");
            return userList;
        }
    }

其他文件，如sqlMapConfig.xml和UserMapper.xml等中的配置和之前的一致

运行结果

![4814873d8044f207a7e1a71e049e5b39.png][]

### 2、代理开发方式 ###

介绍

采用Mybatis的电路考法方式实现Dao层的开发，这种方式是我们进入企业的主流。

Mapper接口开发方法只需要程序员编写Mapper接口(相当于Dao接口)，由Mybatis框架根据接口定义创建接口的动态代理对象，代理对象的方法体同上边Dao接口实现类方法。 Mapper接口开发需要遵循以下规范:

1.Mapper.xml文件中的namespace与mapper接口的全限定名相同  
2.Mapper接口方法名和Mapperxml中定义的每个statement的id相同  
3.Mapper接口方法的输入参数类型和mapper.xml中定义的每个sql的parameterType的类型相同  
4.Mapper接口方法的输出参数类型和mapper.xml中定义的每个sql的resultType的类型相同  
规范图示对应

![4b3309c44f3f26b4b8e106d3abb34275.png][]

代码测试代理开发

> UserDao下

package com_Dao_DaiLi.Dao;
    import com_mybatis.pojo.User;
    import java.io.IOException;
     
    public interface  UserDao {
        public User findById(int id) throws IOException;
    }

> service包下

package com_Dao_DaiLi.service;
     
    import com_Dao_DaiLi.Dao.UserDao;
    import com_mybatis.pojo.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 java.io.IOException;
    import java.io.InputStream;
     
    public class ServiceTest {
        public static void main(String[] args) throws IOException {
            InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();
     
            UserDao mapper = sqlSession.getMapper(UserDao.class);
            User user = mapper.findById(1);
            System.out.println(user);
     
        }
    }

> UserMapper1.xml下

<?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">
    <mapper namespace="com_Dao_DaiLi.Dao.UserDao">
     
     
    
        <select id="findById" parameterType="int" resultType="user">
            select *from user where id=#{id}
        </select>
     
     
     
    </mapper>

> 还需注意将sqlMapConfig.xml下加载UserMapper1.xml下

![bf12e77e968279847fc81dd8e3d88806.png][]

运行结果

![2fee09410f86b1744894e1676904859d.png][]

[cc0d24fa3e226c786c7e7b8ea486ab81.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/20d2816a1cd846fa9ba04727af264855.png
[852c125f389d9dd576ad95b2dd37a4d5.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/1c0486a06db44cba90d4df43cc7829b0.png
[3cfe9cc35503be7ce68be1a29d7c759c.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/016b6a609581490d8e97033fde8ac305.png
[294155fd414efe2caef3e302f66eaaea.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/2df7e84b5a144798a9090199a48c73a9.png
[4814873d8044f207a7e1a71e049e5b39.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/96fb98e412bf4e98a2f72868b762f2f1.png
[4b3309c44f3f26b4b8e106d3abb34275.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/84b30d726756401dbf08542d36c1bbc3.png
[bf12e77e968279847fc81dd8e3d88806.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/c30bdcfc307e4959b196236911ca86c4.png
[2fee09410f86b1744894e1676904859d.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/f7b448790b11486f80f289d208d2eb40.png