IllegalArgumentException：必须管理实体才能调用remove

Question

控制器页面具有以下代码

                BigDecimal id=new BigDecimal(request.getParameter("empId"));
                employee.setEmpno(id);
                flag = factory.removeEmployee(employee);

TransactionFactory类

    public final class EntityTransactionFactory implements TransactionFactory{

    @PersistenceContext
    private EntityManagerFactory Factory;
    private EntityManager Manager;
    @Resource
    private UserTransaction Transaction;
    private static final TransactionFactory transaction = new EntityTransactionFactory();

    private EntityTransactionFactory() {

    }

    public static TransactionFactory getInstance() {
        return transaction;
    }


    /**
     * @return the Factory
     */
    @Override
    public EntityManagerFactory getFactory() {
        Factory= Persistence.createEntityManagerFactory("SampleBeanPU");
        return Factory;
    }

    /**
     * @return the Manager
     */
    @Override
    public EntityManager getManager() {
        Manager=getFactory().createEntityManager();
        return Manager;
    }

    /**
     * @return the Transaction
     */
    @Override
    public UserTransaction getTransaction() {
        try {
            Transaction = (UserTransaction) new InitialContext().lookup("java:comp/UserTransaction");
        } catch (NamingException e) {
            Transaction=null;
        }
        return Transaction;
    }
}

emp Emp类型的变量名称。

        TransactionFactory factory=EntityTransactionFactory.getInstance();
        factory.getTransaction().begin();
        factory.getManager().joinTransaction();

        Emp ref= factory.getManager().getReference(Emp.class, emp.getEmpno());
        System.out.println(ref.getEname());
        factory.getManager().remove(factory.getManager().merge(ref));
        System.out.println(factory.getTransaction().getStatus());
        factory.getTransaction().commit();
        System.out.println(factory.getTransaction().getStatus());
        //factory.getManager().flush();
        factory.getManager().close();
        factory.getFactory().close();

但是，出现以下异常，该异常指向上面的代码。

 java.lang.IllegalArgumentException: Entity must be managed to call remove: com.entity.Emp[ empno=1234 ], try merging the detached and try the remove again.

Answer 1

正如@JBNizet建议的

通过将其放入私有构造函数并通过此类的getter方法检索实例，我仅创建EntityManagerFactory实例一次。

为了删除实体，我使用了以下代码

        Emp ref = factory.getManager().find(Emp.class, emp.getEmpno());           
        factory.getManager().remove(ref);

而且，它有效。