【MyBtis】配置和映射

MyBatis 的真正强大之外在于它的映射语句，这也是它的魅力所在。由于它的异常强大，映射器的XML文件就显得相对简单。如果将其与具有相同功能的 JDBC 代码进行对比，会立即发现其省掉了将近 95% 的代码。MyBatis 就是针对 SQL 构建的并且比普通的方法效果更好。

11.1 示例:实现表数据的增、删、改、查

1.创建工程mybatis_DML demo

在 idea 中创建 Maven Project，如图11-1所示，“GroupID“ 选项中输入 “com.mialab” ，在 “ArtifactId” 选项输入“student”最终完成的 student 工程目录和 student 初始表数据如图11-1和图11-2所示。

图11-1 mybatisDML_demo 工程目录结构

图11-2student表中的数据

2.创建数据库操作的工具类：DBOperatorMgr.java

在MyBatis 使用中，如果每个方法执行时都需要读取配置文件，并根据配置文件的信息构建SqlSessionFactory对象，然后创建SqlSession 对象，这会导致类大量的重复代码。为了简化开发，需要将重复代码封装到一个工具类中。如下：

public class DBOperatorMgr {
	static Logger logger = Logger.getLogger(DBOperatorMgr.class.getName());
	private static DBOperatorMgr dbMgr;
	private SqlSessionFactory sqlSessionFactory;

	private DBOperatorMgr() {
		String resource = "mybatis-config.xml";
		InputStream inputStream;

		try {
			inputStream = Resources.getResourceAsStream(resource);
			sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
		} catch (Exception e) {
			logger.error(e.toString());
		}
	}

	public static DBOperatorMgr getInstance() {
		if (dbMgr == null) {
			dbMgr = new DBOperatorMgr();
		}
		return dbMgr;
	}
	
	public SqlSessionFactory getSqlSessionFactory() {
		return sqlSessionFactory;
	}	
}

3.创建映射接口

public interface StudentMapper {
	public Student getStudent(String sno);

	public int addStudent(Student student);

	public List<Student> getSudentAll();

	public int updateStudent(Student student);

	public int deleteStudent(String sno);
}

4.创建XML映射文件

在包com.mialab.mybatis_DML_demomapper 中创建 StudentMapper.xml文件。

<mapper namespace="com.mialab.mybatis_DML_demo.mapper.StudentMapper">
	<select id="getStudent" resultType="com.mialab.mybatis_DML_demo.domain.Student">
		select * from student where
		sno = #{sno}
	</select>
	<insert id="addStudent" parameterType="student">
		insert into
		student(sno,name,sex,age,dept_no)
		values(#{sno},#{name},#{sex},#{age},#{dept_no})
	</insert>

	<resultMap id="studentResultMap" type="student">
		<id property="sno" column="sno" />
		<result property="name" column="name" />
		<result property="sex" column="sex" />
		<result property="age" column="age" />
		<result property="dept_no" column="dept_no" />
	</resultMap>
	<select id="getSudentAll" resultMap="studentResultMap">
		select * from student
	</select>


	<update id="updateStudent" parameterType="student">
		update student set name
		= #{name}, sex = #{sex}, age = #{age}, dept_no = #{dept_no}
		where sno =
		#{sno}
	</update>

	<delete id="deleteStudent" parameterType="String">
		delete from student
		where sno = #{sno}
	</delete>

</mapper>

5.测试

如图11-1所示，在src/main/java 中创建 Package“com.mialab.mybatis_DML demo.main”。在此包中创建测试类DML_Mainjava，主要代码：

public class DML_Main {	
	
	public static void main(String[] args) {
		//testInsert();
		//testSelectAll();
		testSelect("20171509");
		//testUpdate();
//		testDelete("20171622");
	}	

	private static void testDelete(String sno) {
		Logger log = Logger.getLogger(DML_Main.class);
		SqlSession session = null;
		try {
			session = DBOperatorMgr.getInstance().getSqlSessionFactory().openSession();
			StudentMapper mapper = session.getMapper(StudentMapper.class);			
			mapper.deleteStudent(sno);			
			session.commit();
		} catch(Exception ex) {
			session.rollback();
			ex.printStackTrace();
		} finally {
			if (session != null) {
				session.close();
			}
		}		
	}

	private static void testSelectAll() {
		Logger log = Logger.getLogger(DML_Main.class);
		SqlSession session = null;
		try {
			session = DBOperatorMgr.getInstance().getSqlSessionFactory().openSession();
			StudentMapper mapper = session.getMapper(StudentMapper.class);
			List<Student> stu_list = mapper.getSudentAll();
			for(Student stu:stu_list) {
				//System.out.println(stu);
				log.info(stu);
			}
		} finally {
			if (session != null) {
				session.close();
			}
		}
	}

	private static void testInsert() {
		Logger log = Logger.getLogger(DML_Main.class);
		SqlSession session = null;
		try {
			session = DBOperatorMgr.getInstance().getSqlSessionFactory().openSession();
			StudentMapper mapper = session.getMapper(StudentMapper.class);
			Student student = new Student();
			student.setSno("20171622");
			student.setName("李白");
			student.setAge(88);
			student.setSex("男");
			student.setDept_no("2609");
			log.info(student);
			mapper.addStudent(student);
			session.commit();
		} catch(Exception ex) {
			session.rollback();
			ex.printStackTrace();
		} finally {
			if (session != null) {
				session.close();
			}
		}
	}

	private static void testSelect(String sno) {
		Logger log = Logger.getLogger(DML_Main.class);
		SqlSession session = null;
		try {
			session = DBOperatorMgr.getInstance().getSqlSessionFactory().openSession();
			StudentMapper mapper = session.getMapper(StudentMapper.class);
			Student student = mapper.getStudent(sno);
			//System.out.println(student);
			log.info(student);
		} finally {
			if (session != null) {
				session.close();
			}
		}		
	}
	
	private static void testUpdate() {
		Logger log = Logger.getLogger(DML_Main.class);
		SqlSession session = null;
		try {
			session = DBOperatorMgr.getInstance().getSqlSessionFactory().openSession();
			StudentMapper mapper = session.getMapper(StudentMapper.class);
			Student student = new Student();
			student.setSno("20171622");
			student.setName("苏东坡");
			student.setAge(68);
			student.setSex("女");
			student.setDept_no("2612");
			log.info(student);
			mapper.updateStudent(student);
			session.commit();
		} catch(Exception ex) {
			session.rollback();
			ex.printStackTrace();
		} finally {
			if (session != null) {
				session.close();
			}
		}
	}
}

先测试 testSelectA11() 方法。如图 11-1 所示，右击comm.ialab.mybatis _DML_demo.main包中的DML_Main.java，在弹出的快捷菜单中选择“Run DML_Main.java”选项，在控制台中可以得到以下的结果：

 INFO [main] - Student [sno=20171508, name=李勇, sex=男, age=20, dept_no=2601]
 INFO [main] - Student [sno=20171509, name=刘娟, sex=女, age=19, dept_no=2602]
 INFO [main] - Student [sno=20171622, name=李白, sex=男, age=88, dept_no=2609]

可分别对增、删、改、查的方法testInsert()、testUpdate()等进行测试。