程序涉及到对数据库的增删改的操作时，需要事务的支持，
否则数据库里就会有许多脏数据；
一般增删改业务逻辑都是在service层进行处理，所以对事务的处理也放在service层
使用注解 @Transactional标记需要事务处理的方法

@Service
public class EmployJpaService {

    @Autowired
    private EmployeeJpaReposity employeeJpaReposity;
    /**
     * 保存
     *
     * @param employees
     * @return
     */
    @Transactional
    public List<Employee> save(List<Employee> employees) {
        List<Employee> employeeList = employeeJpaReposity.save(employees);
        return employeeList;
    }

    /**
     * 修改
     * <p>
     * 判断是否存在
     * 不存在 插入
     * 存在 删除
     *
     * @param employee
     */
    @Transactional
    public void update(Employee employee) {
        Integer id = employee.getEmpno();
        boolean exists = employeeJpaReposity.exists(id);
        if (exists) {
            employeeJpaReposity.delete(employee);
        }else {
            employeeJpaReposity.save(employee);
        }

    }
}
----------------------------
测试：
    @Test
    public void testTransaction(){
        Employee employee = new Employee();
        employee.setEmpno(1234);
        employee.setEname("noddles");
        employee.setSal(100.0);
        employee.setJob("coder");
        employee.setDeptno(20);
        employee.setHiredate(new Date(System.currentTimeMillis()));
        employee.setMgr(200);
        employee.setComm(100.0);
        List<Employee> employees = Arrays.asList(employee);
        employJpaService.save(employees);
        Employee one = employeeJpaReposity.findOne(1234);
        System.out.println("更新操作前---------------");
        System.out.println(one);
        boolean exists = employeeJpaReposity.exists(1234);
        System.out.println("------------->"+exists);
         employJpaService.update(employee);
        exists = employeeJpaReposity.exists(1234);
        System.out.println("------------->"+exists);
        one = employeeJpaReposity.findOne(1234);
        System.out.println("更新操作后---------------");
        System.out.println(one);
    }
-------------------------------------------------------------------------
测试结果：
更新操作前---------------
Employee{empno=1234, ename='noddles', job='coder', mgr=200, hiredate=2018-02-07, sal=100.0, comm=100.0, deptno=20}
------------->true
------------->false
更新操作后---------------
null

由于 JpaRepository接口中没提供update 方法，需要update 操作 还需 使用@Query注解，但要在之前加上
@Modifying注解，标识这个是update 或者delete操作！需要事务支持。

  定义接口：
    //更新工资
    @Modifying
    @Query(nativeQuery = true,value = "update EMP set sal=?1 where empno=?2")
    public void updateSal(Double sal,Integer empno);

   service层：
    @Transactional
    public void upateSal(Double sal,Integer enpno){
        employeeJpaReposity.updateSal(sal,enpno);
    }

测试：
    @Test
    public void testUpdateSal(){
        Employee one = employeeJpaReposity.findOne(1234);
        System.out.println("---------更新前--------->"+one);
        employJpaService.upateSal(1200.0,1234);
        one = employeeJpaReposity.findOne(1234);
        System.out.println("---------更新后--------->"+one);
    }
------------------------------------
测试结果：
---------更新前--------->Employee{empno=1234, ename='noddles', job='coder', mgr=200, hiredate=2018-02-07, sal=100.0, comm=100.0, deptno=20}
---------更新后--------->Employee{empno=1234, ename='noddles', job='coder', mgr=200, hiredate=2018-02-07, sal=1200.0, comm=100.0, deptno=20}