Mybatis中配置Mapper的方法

客官°小女子只卖身不卖艺 2022-04-11 06:56 492阅读 0赞

我们知道在Mybatis中定义Mapper信息有两种方式，一种是利用xml写一个对应的包含Mapper信息的配置文件；另一种就是定义一个Mapper接口，然后定义一些相应的操作方法，再辅以相应的操作注解。

现假设我有这样一个实体类：

package com.bijian.model;
    
    public class User {
    
        private int id;
        private String name;
        private int 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;
        }
        
        @Override
        public String toString() {
            return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
        }
    }

它对应的数据库表结构是这样的：

![69191876-d137-3843-b793-fc25001694d7.png][]  
        然后我要利用Mybatis对它做一个简单的增删改查操作，那么如果利用xml配置Mapper的方式来定义的话，我对应的UserMapper.xml文件会是这样：

<?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.bijian.mapper.UserMapper">
        <insert id="insertUser" parameterType="User" useGeneratedKeys="true" keyColumn="id">
           insert into user_tb(name, age) values(#{name}, #{age})
        </insert>
       
        <update id="updateUser" parameterType="User">
           update user_tb set name=#{name}, age=#{age} where id=#{id}
        </update>
       
        <select id="findById" parameterType="int" resultType="User">
           select * from user_tb where id=#{id}
        </select>
       
        <delete id="deleteUser" parameterType="int">
           delete from user_tb where id=#{id}
        </delete>
    </mapper>

如果使用接口加注解的方式，那么我们的UserMapper接口应该这样定义：

package com.bijian.mapperinterface;
    
    import org.apache.ibatis.annotations.Delete;
    import org.apache.ibatis.annotations.Insert;
    import org.apache.ibatis.annotations.Select;
    import org.apache.ibatis.annotations.Update;
    
    import com.bijian.model.User;
    
    public interface UserMapper {
    
        @Insert("insert into user_tb(name, age) values(#{name}, #{age})")
        public void insertUser(User user);
    
        @Update("update user_tb set name=#{name}, age=#{age} where id=#{id}")
        public void updateUser(User user);
    
        @Select("select * from user_tb where id=#{id}")
        public User findById(int id);
    
        @Delete("delete from user_tb where id=#{id}")
        public void deleteUser(int id);
    }

注意看这里我故意把UserMapper接口的namespace也就是它的包名置为与UserMapper.xml的namespace属性不一样。这主要是为了要更好的讲以下的内容。

接下来要做的就是把Mapper信息注册到Mybatis的配置中，告诉Mybatis我们定义了哪些Mapper信息。这主要是在Mybatis的配置文件中通过mappers元素来进行的。在以前版本的Mybatis中我们在Mybatis的配置文件中需要这样定义Mapper信息资源的位置。

这主要是通过mapper元素的resource和url属性来指定的，resource属性指定的是相对于跟类路径下的资源，url属性指定的是通过URL可以获取到的资源。这有一点不好的地方，当我们使用Mapper接口加注解来定义当前Mapper的操作信息时，我们还需要定义一个与它对应的Mapper.xml文件。如：

我发现在现在使用的这个Mybatis3.2.1中这个问题已经得到了改善，现在我们在定义基于接口的定义的Mapper时可以通过一个class属性来指定接口。

这里的一个package只针对于一个包。当在多个包里面定义有Mapper接口时，我们需要定义对应的多个package元素。

这四种注册Mapper的方式就是我想在这篇文章中表达的。总结一下：

当使用mapper元素进行Mapper定义的时候需要注意：mapper的三个属性resource、url和class对于每个mapper元素只能指定一个，要么指定resource属性，要么指定url属性，要么指定class属性，不能都指定，也不能都不指定。

下面将对上面的代码给出一些对应的测试代码。

先看下工程结构图：

![02743dea-229a-368f-84f2-0254021b46e6.png][]

再贴出测试对应的Mybatis的配置文件：

<?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>
        <typeAliases>
            <typeAlias alias="User" type="com.bijian.model.User" />
        </typeAliases>
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC" />
                <dataSource type="POOLED">
                    <property name="driver" value="com.mysql.jdbc.Driver" />
                    <property name="url" value="jdbc:mysql://127.0.0.1:3306/test?characterEncoding=utf8" />
                    <property name="username" value="test" />
                    <property name="password" value="test" />
                </dataSource>
            </environment>
        </environments>
        <mappers>
       		
    		<mapper resource="com/bijian/mapper/UserMapper.xml" />
    		
    		<package name="com.bijian.mapperinterface" />
    	</mappers>
    </configuration>

Util.java

package com.bijian.util;
    
    import java.io.IOException;
    import java.io.Reader;
    
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    
    public class Util {
    
        public static SqlSessionFactory getSqlSessionFactory() {
            
            String resource = "configure.xml";
            Reader reader = null;
            try {
                reader = Resources.getResourceAsReader(resource);
            } catch (IOException e) {
                e.printStackTrace();
            }
    
            SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader);
            return factory;
        }
    }

一.对于使用xml方式定义的UserMapper.xml，然后直接使用SqlSession访问定义在其中的statement的测试：

package com.bijian.test;
    
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.junit.Before;
    import org.junit.Test;
    
    import com.bijian.model.User;
    import com.bijian.util.Util;
    
    /**
     * 这个类主要用来测试直接使用SqlSession访问定义在UserMapper.xml文件中的statement
     */
    public class UserMapperTest {
    
        SqlSessionFactory sqlSessionFactory = null;
    
        @Before
        public void before() {
            sqlSessionFactory = Util.getSqlSessionFactory();
        }
    
        @Test
        public void testInsert() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                User user = new User();
                user.setName("张三");
                user.setAge(30);
                sqlSession.insert("com.bijian.mapper.UserMapper.insertUser", user);
                sqlSession.commit();
            } finally {
                sqlSession.close();
            }
        }
    
        @Test
        public void testUpdate() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                User user = new User();
                user.setId(1);
                user.setName("李四");
                user.setAge(34);
                sqlSession.update("com.bijian.mapper.UserMapper.updateUser", user);
                sqlSession.commit();
            } finally {
                sqlSession.close();
            }
        }
    
        @Test
        public void testFind() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                User user = sqlSession.selectOne("com.bijian.mapper.UserMapper.findById", 1);
                System.out.println(user.getId() + "--" + user.getName() + "--" + user.getAge());
            } finally {
                sqlSession.close();
            }
        }
    
        @Test
        public void testDelele() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                sqlSession.delete("com.bijian.mapper.UserMapper.deleteUser", 2);
                sqlSession.commit();
            } finally {
                sqlSession.close();
            }
        }
    }

二.对于使用Mapper接口加对应的注解来定义的Mapper信息直接使用SqlSession访问Mapper接口中使用注解定义好的statement的测试：

package com.bijian.test;
    
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.junit.Before;
    import org.junit.Test;
    
    import com.bijian.model.User;
    import com.bijian.util.Util;
    
    /**
     *这个类是测试直接使用SqlSession访问UserMapper接口中使用注解定义好的statement
     */
    public class UserMapperTest2 {
    
        SqlSessionFactory sqlSessionFactory = null;
    
        @Before
        public void before() {
            sqlSessionFactory = Util.getSqlSessionFactory();
        }
        
        @Test
        public void testInsert() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                User user = new User();
                user.setName("张三");
                user.setAge(30);
                sqlSession.insert("com.bijian.mapperinterface.UserMapper.insertUser", user);
                sqlSession.commit();
            } finally {
                sqlSession.close();
            }
        }
    
        @Test
        public void testUpdate() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                User user = new User();
                user.setId(1);
                user.setName("李四");
                user.setAge(34);
                sqlSession.update("com.bijian.mapperinterface.UserMapper.updateUser", user);
                sqlSession.commit();
            } finally {
                sqlSession.close();
            }
        }
    
        @Test
        public void testFind() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                User user = sqlSession.selectOne("com.bijian.mapperinterface.UserMapper.findById", 1);
                System.out.println(user.getId() + "--" + user.getName() + "--" + user.getAge());
            } finally {
                sqlSession.close();
            }
        }
    
        @Test
        public void testDelele() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                sqlSession.delete("com.bijian.mapperinterface.UserMapper.deleteUser", 3);
                sqlSession.commit();
            } finally {
                sqlSession.close();
            }
        }
    }

三.对于使用Mapper接口加注解定义好的Mapper信息通过SqlSession获取其对应的Mapper接口来操作其中定义好的statement的测试：

package com.bijian.test;
    
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.junit.Before;
    import org.junit.Test;
    
    import com.bijian.mapperinterface.UserMapper;
    import com.bijian.model.User;
    import com.bijian.util.Util;
    
    /**
     *这个类是测试使用SqlSession获取UserMapper接口来执行使用注解定义在UserMapper接口中的statement
     */
    public class UserMapperTest3 {
    
        SqlSessionFactory sqlSessionFactory = null;
    
        @Before
        public void before() {
            sqlSessionFactory = Util.getSqlSessionFactory();
        }
        
        @Test
        public void testInsert() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                User user = new User();
                user.setName("张三");
                user.setAge(30);
                UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
                userMapper.insertUser(user);
                sqlSession.commit();
            } finally {
                sqlSession.close();
            }
        }
    
        @Test
        public void testUpdate() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                User user = new User();
                user.setId(1);
                user.setName("李四");
                user.setAge(34);
                UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
                userMapper.updateUser(user);
                sqlSession.commit();
            } finally {
                sqlSession.close();
            }
        }
    
        @Test
        public void testFind() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
                User user = userMapper.findById(1);
                System.out.println(user.getId() + "--" + user.getName() + "--" + user.getAge());
            } finally {
                sqlSession.close();
            }
        }
    
        @Test
        public void testDelele() {
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
                userMapper.deleteUser(5);
                sqlSession.commit();
            } finally {
                sqlSession.close();
            }
        }
    }

文章来源：[http://haohaoxuexi.iteye.com/blog/1841033][http_haohaoxuexi.iteye.com_blog_1841033]

[69191876-d137-3843-b793-fc25001694d7.png]: /images/20220411/ebd5ac6ab19f43828e86fa5c6be4a903.png
[02743dea-229a-368f-84f2-0254021b46e6.png]: /images/20220411/8456a8950fe94e32960cf34f79e3250d.png
[http_haohaoxuexi.iteye.com_blog_1841033]: http://haohaoxuexi.iteye.com/blog/1841033