Spring注入属性为null

public class QuestionDTO implements Serializable {

    private static final long serialVersionUID = -3460493378289082953L;
    private Integer pageNum = 1;
    private Integer pageSize = 10;
    private String title;
    private Integer classificationFirst;
    private String classificationFirstName;
    private String startDate;
    private String endDate;
    private Integer status;
    private Long questionId;
    private Integer emergencyStatus;