Mybatis注解开发

Mybatis注解开发其实就是可以省略掉我们的映射文件，直接在接口上编写sql，虽然很方便，但是复杂的sql语句还是使用xml文件来编写更好

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首先，我们需要先创建一个Maven项目，可参考我之前编写的Maven项目的创建

1.导入相关依赖包

<!-- Mybatis核心 -->
<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>3.5.7</version>
</dependency>
<!-- junit测试 -->
<dependency>
  <groupId>junit</groupId>
  <artifactId>junit</artifactId>
  <version>4.12</version>
  <scope>test</scope>
</dependency>
<!-- MySQL驱动 -->
<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>5.1.3</version>
</dependency>
<!-- lombok插件 -->
<dependency>
  <groupId>org.projectlombok</groupId>
  <artifactId>lombok</artifactId>
  <version>1.18.10</version>
</dependency>

2.创建MyBatis的核心配置文件

先配置一个数据库配置文件db.properties，配置文件存放的位置是src/main/resources目录下

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://192.168.111.131:3306/mybatis?characterEncoding=UTF-8
username=root
password=123456

然后创建MyBatis核心配置文件，习惯上命名为mybatis-config.xml，核心配置文件存放的位置是src/main/resources目录下

<?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>
    <!--引入外部配置文件-->
    <properties resource="db.properties"/>

    <settings>
        <!--实体类驼峰命名与数据库_命名映射开启-->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>

    <!--设置连接数据库的环境-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <!--这里绑定的就不是映射文件，注解开发的话要绑定接口文件-->
    <mappers>
        <mapper class="com.chen.mybatis.mapper.UserMapper" />
    </mappers>

</configuration>

3.创建实体类

该地方我们使用的是Lombok配置实体类，可以通过Lombok的配置使用对其进行了解

@AllArgsConstructor
@NoArgsConstructor
@Data
public class User {

    private Integer id;
    private String username;
    private String password;
    private Integer age;
    private String sex;
    private String email;

}

4.创建Mapper接口

MyBatis中的mapper接口相当于以前的dao。在Mybatis注解开发中，我们的sql语句也写在该地方。

public interface UserMapper {

    @Select("select * from t_user")
    List<User> getUser();

    @Select("select * from t_user where id = #{id}")
    User getUsersById(@Param("id")int id);

    @Insert("insert into t_user values(#{id},#{username},#{password},#{age},#{sex},#{email})")
    int addUser(User user);

}

5.编写Mybatis工具类

public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            //读取MyBatis的核心配置文件
            InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
            //创建SqlSessionFactoryBuilder对象
            SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
            //通过核心配置文件所对应的字节输入流创建工厂类SqlSessionFactory，生产SqlSession对象
            sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession(){
        //参数true为设置自动提交
        return sqlSessionFactory.openSession(true);
    }
}

6.测试

getUser语句

public class MybatisTest {
    @Test
    public void testMybatis() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        List<User> userList = userMapper.getUser();
        for(User user:userList){
            System.out.println(user);
        }
        sqlSession.close();
    }
}

 getUsersById语句

public class MybatisTest {
    @Test
    public void testMybatis() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        User user = userMapper.getUsersById(3);
        System.out.println(user);

        sqlSession.close();
    }
}

addUser语句

public class MybatisTest {
 @Test
    public void testMybatis() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        userMapper.addUser(new User(10,"admin","123",11,"man","123@qq.com"));

        sqlSession.close();
    }
}