CDI事件和仿制药 [英] CDI events and generics

问题描述

我正在尝试发送事件并进行一般的操作。我的意思是 - 创建一个具有通用类型的抽象基础DAO类，并从其方法触发事件。这应该适用于所有后代。如果我定义确切的类型，但不是 - 如果我使用泛型，这可以工作。我的意思是：

AbstractDAO（泛型 - 不触发事件）：

  public abstract class AbstractDAO< T extends Persistable>实现Serializable {
 @Inject @PostSaveEvent Event< T> postSaveEvent; 
 
 public T saveOrUpdate（T object）throws DatabaseException {
 T obj = em.merge（object）; 
 
 postSaveEvent.fire（obj）; 
} 
} 
  

AbstractDAO（没有泛型，只是简单的类公开抽象类AbstractDAO< T扩展可持续性> $ / $实现Serializable {
@Inject @PostSaveEvent Event< Polis> postSaveEvent;

public T saveOrUpdate（T object）throws DatabaseException {
T obj = em.merge（object）;

postSaveEvent.fire（（Polis）obj）;
}
}

PolisDAO类扩展了AbstractDAO并定义了通用类型：

  @Stateless 
 @Named 
 @PolisType 
 public class PolisDAO扩展了AbstractDAO< Polis> ; {
 //某些方法（saveOrUpdate不被覆盖）
} 
  

我的观察员类：

  @Stateless 
 @Named 
 public class ProlongationService {
 
 public void attachProlongationToPolisOnSave（@Observes @PostSaveEvent Polis polis）throws DatabaseException {
 // ...使用polis对象进行smth。这不是在第一种情况下调用，而是在第二个
 
中调用
  

对于我来说奇怪，因为CDI事件的 fire（）方法应该在运行时定义事件类型，而不是在编译或部署期间...当我调试时，我看到

  postSaveEvent.fire（obj）;第一个样本的
  

与Polis实体完全一致。但是没有发生任何事件...

更新。我尝试了基础泛型类，但没有运气：

  @Inject @PostSaveEvent事件< Persistable> postSaveEvent; 
  

谢谢。

解决方案

在理论上应该是有效的，但实际上在Java Reflection中运行时检查通用对象的类型有时是不可能的。这是由于类型擦除。 IIRC具体子类的类型没有被清除，所以应该可以重新连接这个，但我猜这个实现现在不是这样做的。

将其作为 http://issues.jboss.org/browse/WELD 问题的错误提交跟踪器（如果您使用的是Weld），以您提供的课程为例，我们可以尝试修复。

要解决问题，请尝试将事件注入具体的子类，并将其作为参数传递，或使用访问器方法将其转换为抽象超类。

I'm trying to send events and do this generically. I mean - create one abstract base DAO class with generic type and fire the event from its method. This should work for all descendants. This works if I define the exact type, but doesn't - if I use generics. What I mean:

AbstractDAO (with generics - doesn't fire the event):

public abstract class AbstractDAO<T extends Persistable> implements Serializable {
   @Inject @PostSaveEvent Event<T> postSaveEvent;

   public T saveOrUpdate(T object) throws DatabaseException {
      T obj = em.merge(object);

      postSaveEvent.fire(obj);
   }
}

AbstractDAO (no generics, just simple class cast - fires the event):

public abstract class AbstractDAO<T extends Persistable> implements Serializable {
   @Inject @PostSaveEvent Event<Polis> postSaveEvent;

   public T saveOrUpdate(T object) throws DatabaseException {
      T obj = em.merge(object);

      postSaveEvent.fire((Polis)obj);
   }
}

PolisDAO class, which extends AbstractDAO and defines the generic type:

@Stateless
@Named
@PolisType
public class PolisDAO extends AbstractDAO<Polis> {
   // some methods (saveOrUpdate is not overriden!)
}

My observer class:

@Stateless
@Named
public class ProlongationService {

    public void attachProlongationToPolisOnSave(@Observes @PostSaveEvent Polis polis) throws DatabaseException {
        // ... DO smth with polis object. This is NOT called in the first case and  called in the second
    }

THis is very strange for me, as "fire()" method for CDI event should define the event type on runtime, not during compilation or deployment... When I debug, I see, that

postSaveEvent.fire(obj);

from the first sample operates exactly with Polis entity. But no event is fired nevertheless...

Upd. I tried the base generic class, but no luck:

@Inject @PostSaveEvent Event<Persistable> postSaveEvent;

Thanks.

解决方案

This should, in theory, work, however in practice inspecting the type of generic objects at runtime with Java Reflection is, at times, impossible. This is due to type erasure. IIRC the type of the concrete sub class isn't erased, so it should be possible to reconnect this, but I guess the implementation isn't doing this right now.

File this as a bug in the http://issues.jboss.org/browse/WELD issue tracker (if you are using Weld), with the classes you provide as an example and we can try to fix it.

To work around, try injecting the event into the concrete subclass, and passing it as an argument, or using an accessor method, to get it into the abstract super class.

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