问无法通过反射hibernate JPA + GF 4获取字段值

EN

@Entity  
@Table(name="purchaseorder")
@PersistenceUnit(name="dstarwarehouse",unitName="dstarwarehouse")
public class PurchaseOrder implements Serializable{

    @Id @GeneratedValue(strategy=GenerationType.AUTO)
    private int idpurchaseorder; 
    private boolean cash;
    private boolean credit;
    private String supplier;
    private String orderedBy;
    private String submittedBy;
    private String approvedBy;
    private Date expectedDate;
    private Date creationDate;
    private Date submittedDate;
    private Date approvalDate;
    private String purchaserName;

    private double total;

    @JoinColumn(name="idpurchaseorder", referencedColumnName="idpurchaseorder")
    private List<Part> parts;