MyBatis 笔记（二）——XML vs 注解

心已赠人 2022-06-10 13:09 206阅读 0赞

MyBatis 支持注解和 XML 两种配置。这一节延续 MyBatis 笔记（一）继续讲。

# 1. 基于 XML 的配置 #

基于 XML 的配置其实和 MyBatis 笔记（一）几乎是一样的。先看最基础的配置文件：

<?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>
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC"/>
                <dataSource type="POOLED">
                    <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql://127.0.0.1:3306/test?useSSL=true"/>
                    <property name="username" value="root"/>
                    <property name="password" value="123456"/>
                </dataSource>
            </environment>
        </environments>
    
        <mappers>
            
            <mapper resource="edu/wzm/mybatis/mapping/PersonMapper.xml"/>
        </mappers>
    </configuration>

最后一行指向 XML 映射文件，XML 映射文件配置要执行的 SQL 语句：

<?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="edu.wzm.mybatis.mapping.PersonMapper">
      
    
      <insert id="insert" parameterType="edu.wzm.mybatis.domain.Person">
        insert into person(name, age) values(#{name}, #{age})
      </insert>
    
      <select id="getById" resultType="edu.wzm.mybatis.domain.Person">
        select *
        from person
        where id = #{id}
      </select>
    
      <select id="getAll" resultType="edu.wzm.mybatis.domain.Person">
        select * from person;
      </select>
    
      <update id="update" parameterType="edu.wzm.mybatis.domain.Person">
        update person set age = #{age} where id = #{id}
      </update>
    
      <delete id="delete" parameterType="int">
        delete from person where id = #{id}
      </delete>
    </mapper>

在用 MyBatis 调用这些 SQL 语句时，需要写出 XML 的全路径，同时加上每个 SQL 语句的 id 名：

public class PersonServices {
        
    
        public void add(){
            Person person = new Person("Alice", 30);
            SqlSession sqlSession = MyBatisUtils.getSqlSession(true);
            /**
             * 映射sql的标识字符串。
             * edu.wzm.mybatis.mapping.PersonMapper是PersonMapper.xml中mapper标签的namespace属性的值，
             * insert是insert标签的id属性值，通过update标签的id属性值就可以找到要执行的SQL。
             */
            int result = sqlSession.insert("edu.wzm.mybatis.mapping.PersonMapper.insert", person);
    
            System.out.println(result);
            sqlSession.close();
        }
    
        public void getAll(){
            SqlSession sqlSession = MyBatisUtils.getSqlSession();
            List<Person> persons = sqlSession.selectList("edu.wzm.mybatis.mapping.PersonMapper.getAll");
    
            System.out.println(persons);
    
            sqlSession.close();
        }
    
        public void getById(){
            SqlSession sqlSession = MyBatisUtils.getSqlSession();
            Person person = sqlSession.selectOne("edu.wzm.mybatis.mapping.PersonMapper.getById", 1);
    
            System.out.println(person);
    
            sqlSession.close();
        }
    
        public void update(){
            Person person = new Person();
            person.setId(7);
            person.setAge(27);
    
            SqlSession sqlSession = MyBatisUtils.getSqlSession(true);
            int result = sqlSession.update("edu.wzm.mybatis.mapping.PersonMapper.update", person);
    
            System.out.println(result);
    
            sqlSession.close();
        }
    
        public void delete(){
            SqlSession sqlSession = MyBatisUtils.getSqlSession(true);
            int result = sqlSession.update("edu.wzm.mybatis.mapping.PersonMapper.delete", 6);
            System.out.println(result);
    
            sqlSession.close();
        }
    }

# 2. 基于注解的配置 #

这里我们只看配置这部分，其他部分和 MyBatis 笔记（一）一样。首先是最基础的配置文件：

<?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>
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC"/>
                <dataSource type="POOLED">
                    <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql://127.0.0.1:3306/test?useSSL=true"/>
                    <property name="username" value="root"/>
                    <property name="password" value="123456"/>
                </dataSource>
            </environment>
        </environments>
    
        <mappers>
            
            <mapper class="edu.wzm.mybatis.mapping.PersonMapper"/>
        </mappers>
    </configuration>

最后一行配置指向注解配置的 Mapping 映射文件。这个映射文件是 Java 的接口，每个方法上面会用注解配置 SQL 语句：

public interface PersonMapper {
        
    
        @Insert("insert into person(name, age) values(#{name}, #{age})")
        public int add(Person person);
    
        @Select("select * " +
                "from person " +
                "where id = #{id}")
        public Person getById(int id);
    
        @Select("select * from person")
        public List<Person> getAll();
    
        @Update("update person set age = #{age} where id = #{id}")
        public int update(Person person);
    
        @Delete("delete from person where id = #{id}")
        public int deleteById(int id);
    
    }

在启动 MyBatis 访问数据库时，也和 XML 不同。它不需要写 XML 映射文件的全路径，直接指定接口名即可：

public class PersonServices {
    
        public void add(){
            Person person = new Person("Kim", 30);
            SqlSession sqlSession = MyBatisUtils.getSqlSession(true);
            PersonMapper mapper = sqlSession.getMapper(PersonMapper.class);
            int result = mapper.add(person);
    
            System.out.println(result);
            sqlSession.close();
        }
    
        public void getAll(){
            SqlSession sqlSession = MyBatisUtils.getSqlSession();
            PersonMapper mapper = sqlSession.getMapper(PersonMapper.class);
            List<Person> person = mapper.getAll();
    
            System.out.println(person);
    
            sqlSession.close();
        }
    
        public void getById(){
            SqlSession sqlSession = MyBatisUtils.getSqlSession();
            PersonMapper mapper = sqlSession.getMapper(PersonMapper.class);
            Person person = mapper.getById(1);
    
            System.out.println(person);
    
            sqlSession.close();
        }
    
        public void update(){
            SqlSession sqlSession = MyBatisUtils.getSqlSession(true);
            PersonMapper mapper = sqlSession.getMapper(PersonMapper.class);
    
            Person person = new Person();
            person.setId(6);
            person.setAge(50);
            int result = mapper.update(person);
    
            System.out.println(result);
    
            sqlSession.close();
        }
    
        public void delete(){
            SqlSession sqlSession = MyBatisUtils.getSqlSession(true);
            PersonMapper mapper = sqlSession.getMapper(PersonMapper.class);
    
            int result = mapper.deleteById(7);
    
            System.out.println(result);
    
            sqlSession.close();
        }
    }

[查看完整代码][Link 1]

[Link 1]: https://github.com/GatsbyNewton/learning-mybatis