MyBatis 笔记（二）——XML vs 注解

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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>        <!-- 基于XML配置文件 -->        <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"><!--  为这个mapper指定一个唯一的namespace，namespace的值习惯上设置成包名+sql映射文件名，这样就能够保证namespace的值是唯一的  例如：namespace="edu.wzm.mybatis.mapping.PersonMapper"(userMapper.xml文件去除后缀)--><mapper namespace="edu.wzm.mybatis.mapping.PersonMapper">  <!--    在select、insert、update、delete标签中编写查询的SQL语句， 设置标签的id属性值必须是唯一的，不能够重复。使用parameterType属性    指明查询时，使用的参数类型。resultType属性指明查询返回的结果集类型，resultType="edu.wzm.mybatis.domain.Person"就表示将查询    结果封装成一个Person类的对象返回，Person类就是person表所对应的实体类。  -->  <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>        <!-- 基于注解 -->        <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();    }}

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