mybatis面向接口式的数据库操作

面向接口式的数据库操作

在mybatis中可以动态为我们生成dao接口的实现类

mybatis当中实际上使用了代理模式，在内存中生成dao接口的代理类，然后创建代理类的实例

使用mybatis的这种代理机制的前提：SqlMapper.xml文件中namespace必须是dao接口的全限定名称，id必须是dao接口中的方法名，mybatis-config中的mapper标签改为package标签，并指明mapper接口的包；mapper.xml文件需要放在同mapper接口相同的包路径下，文件名要与接口名相同

mybatis-config配置文件

    <mappers>
        <!-- 指定mapper接口的包 -->
        <package name="com.atli.mapper"/>
    </mappers>

工具类

public class SqlSessionUtil {
    // 全局唯一的工厂对象
    private static SqlSessionFactory sqlSessionFactory;
    // 全局唯一的线程资源管理
    private static ThreadLocal<SqlSession> local = new ThreadLocal<SqlSession>();

    // 工厂对象是全局唯一的，在类加载时创建刚好满足需求
    static{
        String resource = "mybatis-config.xml";
        try {
            // 通过流读取配置文件并使用build方法创造工厂对象
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader(resource));
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static SqlSession getSqlSession(){
        // 获取SqlSession时，若当前线程SqlSession为空就new一个并绑定在当前线程
        if(local.get() == null){
            local.set(sqlSessionFactory.openSession());
        }
        return local.get();

    }

    public static void closeSqlSession(){
        if(local.get() != null){
            local.get().close();
            local.remove();
        }
    }
}

mapper层

public interface StudentMapper {
    int addStudent(Student student);

    int updateStudent(Student student);

    int deleteStudent(int id);

    Student getStudentById(int id);

    List<Student> getAllStudent();
}

mapper配置文件

<!-- 放在resources/com/atli/mapper目录下,且命名为StudentMapper -->
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- 命名空间是使用的mapper接口的全类名 -->
<mapper namespace="com.atli.mapper.StudentMapper">
    <!-- 方法id要与mapper接口中方法名相同 -->
    <insert id="addStudent" parameterType="com.atli.pojo.Student">
        <!-- 所插入的变量名要与mapper接口中变量名相同 -->
        insert into student (stu_id, stu_name, stu_age, classes_id) value (#{stuId},#{stuName},#{stuAge},#{classesId})
    </insert>
    <update id="updateStudent" parameterType="com.atli.pojo.Student">
        update student set stu_name=#{stuName}, stu_age=#{stuAge}, classes_id=#{classesId}
    </update>
    <delete id="deleteStudent">
        delete from student where stu_id=#{stuId}
    </delete>
    <select id="getStudentById" resultType="com.atli.pojo.Student">
        select * from student where stu_id=#{stuId}
    </select>
    <select id="getAllStudent" resultType="com.atli.pojo.Student">
        select * from student
    </select>
</mapper>

service实现类

public class StudentServiceImpl implements StudentService {
    @Override
    public int addStudent(Student student) {
        SqlSession sqlSession = SqlSessionUtil.getSqlSession();
        // SqlSession的getMapper提供了对于Mapper的一个代理，可以直接调用配置文件中sql语句
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        return mapper.addStudent(student);
    }

    @Override
    public int updateStudent(Student student) {
        SqlSession sqlSession = SqlSessionUtil.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        return mapper.updateStudent(student);
    }

    @Override
    public int deleteStudent(int id) {
        SqlSession sqlSession = SqlSessionUtil.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        return mapper.deleteStudent(id);
    }

    @Override
    public Student getStudentById(int id) {
        SqlSession sqlSession = SqlSessionUtil.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        return mapper.getStudentById(id);
    }

    @Override
    public List<Student> getAllStudent() {
        SqlSession sqlSession = SqlSessionUtil.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        return mapper.getAllStudent();
    }
}