Mybatis的Mapper动态代理方式连接mysql数据库

女爷i 2022-05-17 08:10 305阅读 0赞

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接口的类路径相同。**
2.  **Mapper接口方法名和Mapper.xml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**

--------------------

### 1.UserMapper.xml(映射文件) ###

定义mapper映射文件UserMapper.xml（内容同Users.xml），需要修改namespace的值为 UserMapper接口路径。将UserMapper.xml放在classpath 下mapper目录 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="mybatisMapper.UserMapper">
    
        
    	<select id="findUserById" parameterType="int" resultType="mybatis.User">
    		 select * from user where id = #{id}
    	</select>
    	
    	
    	<select id="countLineNumbers"  resultType="int">
    		 select count(*) from user
    	</select>
    	
        
    	<select id="findUserByUsername" parameterType="String" resultType="mybatis.User">
    	     select * from user where username like '%${value}%' 
    	</select>
    	
        
    	<insert id="insertUser" parameterType="mybatis.User">
    	     <selectKey keyProperty="id" order="AFTER" resultType="Integer">
    		     select LAST_INSERT_ID()
    	     </selectKey>
    	     insert into user(username,birthday,sex,address) values(#{username},#{birthday},#{sex},#{address})
        </insert>
         
    </mapper>

### 2.Mapper.java(接口文件) ###

package mybatisMapper;
    
    import java.util.List;
    import mybatis.User;
    
    /**
     * 用户管理mapper的接口
     */
    public interface UserMapper {
    	
    	//根据用户id查询用户信息
    	public User findUserById(int id);
    	//查询用户列表
    	public List<User> findUserByUsername(String username);
    	//添加用户信息
    	public void insertUser(User user); 
    	//获取数据库行数
    	public int countLineNumbers();
    }

接口定义有如下特点：

1.  Mapper接口方法名和UserMapper.xml中定义的statement的id相同
2.  Mapper接口方法的输入参数类型和UserMapper.xml中定义的statement的parameterType的类型相同
3.  Mapper接口方法的输出参数类型和UserMapper.xml中定义的statement的resultType的类型相同

### 3.SqlMapConfig.xml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">
    
    <configuration>
        <properties resource="db.properties"/>
    	
    	<environments default="development">
    		<environment id="development">
    		
    			<transactionManager type="JDBC" />
    		
    			<dataSource type="POOLED">
    				<property name="driver" value="${jdbc.driver}" />
    				<property name="url" value="${jdbc.url}" />
    				<property name="username" value="${jdbc.username}" />
    				<property name="password" value="${jdbc.password}" />
    			</dataSource>
    		</environment>
    	</environments>	
    	
    	<mappers>
    		 <mapper resource="sqlmap/User.xml"/>
    		 
    		 <mapper resource="mapper/UserMapper.xml"/> 				
        </mappers>
       
    </configuration>

### 4.测试文件 ###

package mybatisMapper;
    
    import java.io.InputStream;
    import java.util.List;
    import junit.framework.TestCase;
    import mybatis.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.Before;
    
    /**
    *类描述:测试动态代理测试方式利用mybatis连接数据库
    *@author: 张宇
    *@date: 日期: 2018年8月8日 时间: 上午10:36:24
     */
    
    public class UserMapperTest extends TestCase {
    
    	private SqlSessionFactory sqlSessionFactory;
    	
    	@Before
    	protected void setUp() throws Exception {
    		//mybatis配置文件
    		String resource = "sqlMapConfig.xml";
    		InputStream inputStream = Resources.getResourceAsStream(resource);
    		//使用SqlSessionFactoryBuilder创建sessionFactory
    		sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    	}
    	
    	/*public void testFindUserById() throws Exception {
    		//获取session
    		SqlSession session = sqlSessionFactory.openSession();
    		//获取mapper接口的代理对象
    		UserMapper userMapper = session.getMapper(UserMapper.class);
    		//调用代理对象方法
    		User user = userMapper.findUserById(93);
    		System.out.println(user);
    		//关闭session
    		session.close();
    		
    	}
    		
        public void testFindUserByUsername() throws Exception {
    		SqlSession sqlSession = sqlSessionFactory.openSession();
    		UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    		List<User> list = userMapper.findUserByUsername("张");
    		System.out.println(list.size());
    
    	}*/
    	
        /*public void testInsertUser() throws Exception {
    		//获取session
    		SqlSession session = sqlSessionFactory.openSession();
    		//获取mapper接口的代理对象
    		UserMapper userMapper = session.getMapper(UserMapper.class);
    		//要添加的数据
    		User user = new User();
    		user.setUsername("张三");
    		user.setBirthday(new Date());
    		user.setSex("1");
    		user.setAddress("北京市");
    		//通过mapper接口添加用户
    		userMapper.insertUser(user);
    		//提交
    		session.commit();
    		//关闭session
    		session.close();
    	}*/
    	
    	public void testCountLineNumbers() throws Exception {
    		//获取session
    		SqlSession session = sqlSessionFactory.openSession();
    		//获取mapper接口的代理对象
    		UserMapper userMapper = session.getMapper(UserMapper.class);
    		//调用代理对象方法
    		int count = userMapper.countLineNumbers();
    		System.out.println(count);
    		//关闭session
    		session.close();		
    	}
    }

mybatis官方推荐使用mapper代理方法开发mapper接口，程序员不用编写mapper接口实现类，使用mapper代理方法时，输入参数可以使用pojo包装对象或map对象，保证dao的通用性。