public String execute(){
		LibraryManagementFacade facade = new LibraryManagementFacade();
		String retValue = SUCCESS ;
		if(getSubmit() != null && SUBMIT.equals(getSubmit())) {
			try {
				setStudentVO(facade.updateStudent(getStudentVO())); 
				if(studentVO != null){
					this.setId(getStudentVO().getId());
					addActionError("Update successfully");
				}
			} catch (LibraryManagementException e) {
				retValue = ERROR;
			}
		} else {
			StudentVO requestVO = new StudentVO();
			requestVO.setId(getId());
			try {
				studentVO = facade.showUser(requestVO);
			} catch (LibraryManagementException e) {
				retValue = ERROR;
			}

		}
		
		return retValue;
	}