mybatis（面向接口编程、注解开发、@Param注解）

1、面向接口编程

（1）面向接口编程的优点

解耦、可扩展、提高复用、分层开发中，上层不用管具体的实现，大家都遵循共同的标准，提高代码的规范性

（2）对接口的理解

定义（规范、约束）与实现的分离

反映了设计人员对系统的抽象理解

接口有两类：抽象体（对一个个体的抽象）和抽象面（对一个个体某一方面的抽象），一个个体可以有多个抽象面

2、使用注解开发

（1）接口：

  @Select("select * from student")
    List<Student> getStudents();

（2）配置文件（核心配置文件，不用再对mapper.xml进行配置）

<mappers>
    <mapper class="pers.zhb.mapper.StudentMapper"></mapper>
</mappers>

（3）测试：

    @Test
    public void testZhuJie(){
        SqlSession sqlSession= MybatisUtils.getSqlSession();
        StudentMapper studentMapper=sqlSession.getMapper(StudentMapper.class);
        List<Student> students=studentMapper.getStudents();
        for (Student student : students) {
            System.out.println(student);
        }
        sqlSession.close();
    }

DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - Opening JDBC Connection
DEBUG [main] - Created connection 249155636.
DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@ed9d034]
DEBUG [main] - ==>  Preparing: select * from student 
DEBUG [main] - ==> Parameters: 
DEBUG [main] - <==      Total: 11
Student{studentno='201811', sname='zhai', sex='男', birthday='1998-11-11', classno='80501', point='890', phone='1234567890', email='null', clas=null}
Student{studentno='201812', sname='zhai2', sex='男', birthday='1998-11-11', classno='80601', point='893', phone='19837372533', email='null', clas=null}
Student{studentno='201813', sname='zhai3', sex='男', birthday='1998-11-11', classno='80501', point='892', phone='19837372534', email='null', clas=null}
Student{studentno='201814', sname='zhai3', sex='男', birthday='1998-11-11', classno='80501', point='892', phone='19837372534', email='null', clas=null}
Student{studentno='201815', sname='qwerr', sex='男', birthday='1998-11-11', classno='80501', point='892', phone='19837372534', email='null', clas=null}
Student{studentno='201816', sname='jiayou', sex='男', birthday='1998-11-11', classno='80501', point='892', phone='19837372534', email='null', clas=null}
Student{studentno='201817', sname='null', sex='null', birthday='null', classno='2', point='null', phone='null', email='null', clas=null}
Student{studentno='201818', sname='null', sex='null', birthday='null', classno='2', point='null', phone='null', email='null', clas=null}
Student{studentno='2', sname='2', sex='2', birthday='null', classno='null', point='null', phone='2', email='null', clas=null}
Student{studentno='1', sname='1', sex='1', birthday='null', classno='null', point='null', phone='1', email='null', clas=null}
Student{studentno='21', sname='21', sex='21', birthday='null', classno='null', point='null', phone='21', email='null', clas=null}
DEBUG [main] - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@ed9d034]
DEBUG [main] - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@ed9d034]
DEBUG [main] - Returned connection 249155636 to pool.

使用注解来映射简单语句会使代码显得更加简洁，但对于稍微复杂一点的语句，Java 注解不仅力不从心，还会让你本就复杂的 SQL 语句更加混乱不堪。 因此，如果你需要做一些很复杂的操作，最好用 XML 来映射语句。摘自：（https://mybatis.org/mybatis-3/zh/getting-started.html）

3、注解实现增删改查

自动提交事务（mybatis工具类）：

    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession(true);//不需要手动提交
    }

在使用注解的方式进行增删改查的操作的时候，不再需要对mapper.xml进行配置，只需要在核心配置文件中添加如下代码：

<mappers>
    <mapper class="pers.zhb.mapper.StudentMapper"></mapper>
</mappers>

（1）查询：

  @Select("select * from student where studentno=#{id}")
    Student findStudentById(@Param("id") Integer studentno);

    @Test
    public void testZhuJie(){
        SqlSession sqlSession= MybatisUtils.getSqlSession();
        StudentMapper studentMapper=sqlSession.getMapper(StudentMapper.class);
        Student student=studentMapper.findStudentById(201816);
        System.out.println(student);
        sqlSession.close();
    }

（2）添加：

  @Insert(" insert into student(studentno,sname,sex,phone) values (#{studentno},#{sname},#{sex},#{phone})")
    int addStudent(Student student);

 @Test
    public void testZhuJie(){
        SqlSession sqlSession= MybatisUtils.getSqlSession();
        StudentMapper studentMapper=sqlSession.getMapper(StudentMapper.class);
        Student student=new Student();
        student.setStudentno("20200426");
        student.setSname("tom");
        student.setSex("女");
        student.setPhone("12345678901");
        studentMapper.addStudent(student);
        sqlSession.close();
    }

（3）修改：

    @Update("update student set phone=#{phone} where studentno=#{studentno}")
    int updateStudent(Student student);

    @Test
    public void testZhuJie(){
        SqlSession sqlSession= MybatisUtils.getSqlSession();
        StudentMapper studentMapper=sqlSession.getMapper(StudentMapper.class);
        Student student=new Student();
        student.setStudentno("20200426");
        student.setPhone("20191817161");
        studentMapper.updateStudent(student);
        sqlSession.close();
    }

 （4）删除：

 @Delete("delete from student where studentno=#{id}")
    int deleteStudent(@Param("id") Integer studentno);

    @Test
    public void testZhuJie(){
        SqlSession sqlSession= MybatisUtils.getSqlSession();
        StudentMapper studentMapper=sqlSession.getMapper(StudentMapper.class);
        studentMapper.deleteStudent(20200426);
        sqlSession.close();
    }

与使用配置文件的方式相比，在增删改查的时候，使用注解的方式去除了对mapper.xml配置文件的配置，只需要对接口进行定义（在接口中书写注解），以及书写测试类。当然，二者都需要被核心配置文件引入。

4、关于@Param注解

（1）基本数据类型或者String类型，需要添加@Param

（2）引用数据类型不需要

（3）如果只有一个基本的数据类型的话，可以忽略

（4）在SQL中引用的就是我们这里的@Param中设定的属性名

    @Select("select * from student where studentno=#{id}")
    Student findStudentById(@Param("id") Integer studentno);