JavaEE CDI中的Weld：Generic Events？ [英] JavaEE CDI in Weld: Generic Events?

问题描述

我对基于泛型的特定事件处理有一个想法，但似乎Weld无法处理它们。我问谷歌，但找不到替代CDI扩展。

问题：是否有CDI扩展名，可处理泛型类型事件的事件传播？

我有三个一般事件，EntityCreated，EntityChanged和EntityDeleted 。它们的基类是这样定义的：

  public abstract class DatabaseEvent< TargetType> {
 
 public TargetType target; 
 
 public DatabaseEvent（TargetType target）{
 this.target = target; 
 
 
 $ / code> 

事件是简单的继承类：

  public class EntityCreatedEvent< TargetType>扩展DatabaseEvent< TargetType> {
 
 public EntityCreatedEvent（TargetType target）{
 super（target）; 
 
 
  

我像这样解雇他们：

  public abstract class MyHome< EntityType> {
 
私有EntityType实体; 
 
 @Inject 
事件< EntityCreatedEvent< EntityType>> entityCreatedEvent; 
 
 public void fireCreatedEvent（）{
 EntityCreatedEvent< EntityType> payload = new EntityCreatedEvent< EntityType>（entity）; 
 entityCreatedEvent.fire（payload）; 
 
 
  

我想要像这样观察它们：

  public void handleProjectCreated（@Observes EntityCreatedEvent< Project> event）{...} 
  

启动服务器Weld告诉我它无法处理泛型事件。 CDI的做法是使用额外的限定符代替泛型来区分它们，例如：



  public void handleProjectCreated （@Observes @ProjectEvent EntityCreatedEvent event）{...} 
  

但是， MyHome 基类，我不能用 @ProjectEvent 来触发它：它可能不是一个项目，而是另一个

到目前为止，我的解决方案是跳过这个输入并像这样处理它们：

  public void handleProjectCreated（@Observes EntityCreatedEvent event）{
 if（event.target instanceof Project）{...} 
} 
  
 
 
 
这个解决方案是可以的，但并不完美。  
解决方案
我想你可以用dinamically绑定限定符成员来做到这一点。这就是你的代码的样子：
  public abstract class MyHome {
 
 private EntityType entity; 
 
 @Inject 
事件< EntityCreatedEvent> entityCreatedEvent; 
 
 public void fireCreatedEvent（）{
 entityCreatedEvent.select（getTypeBinding（））。fire（new EntityCreatedEvent（entity））; 
} 
 
 private TypeBinding getTypeBinding（）{
返回新的TypeBinding（）{
 public Class< ;?扩展EntityType> value（）{return entity.getClass（）;} 
}; 
 
 
 @Qualifier 
 @Target（{PARAMETER，FIELD}）
 @Retention（RUNTIME）
 public @interface EntityTypeQualifier {
类< ;?扩展EntityType>值（）; 
} 
 
公共抽象类TypeBinding扩展AnnotationLiteral< EntityTypeQualifier> implements EntityTypeQualifier {} 
 
 // Observers 
 public void handleEntityType1Created（@Observes @EntityTypeQualifier（EntityType1.class）EntityCreatedEvent event）{} 
 public void handleEntityType2Created（@Observes @EntityTypeQualifier EntityType2.class）EntityCreatedEvent event）{} 
  
 
I have an idea for a specific event handling based on generics, but seems like Weld can't handle them. I asked google but couldn't find an alternative CDI extension for this. 


Question: is there a CDI extension, that can handle event propagation of generic-typed events? 

In the following the explicit problem I have.

I have three general events, EntityCreated, EntityChanged and EntityDeleted. The base class for them is defined like this: 
public abstract class DatabaseEvent<TargetType> {

    public TargetType target;

    public DatabaseEvent(TargetType target) {
        this.target = target;
    }
}
The events then are simple inherited classes:
public class EntityCreatedEvent<TargetType> extends DatabaseEvent<TargetType> {

    public EntityCreatedEvent(TargetType target) {
        super(target);
    }
}
I fire them like this:
public abstract class MyHome<EntityType> {

    private EntityType entity;

    @Inject
    Event<EntityCreatedEvent<EntityType>> entityCreatedEvent;

    public void fireCreatedEvent() {
        EntityCreatedEvent<EntityType> payload = new EntityCreatedEvent<EntityType>(entity);
        entityCreatedEvent.fire(payload);
    }
}
I want to observe them like this:
public void handleProjectCreated(@Observes EntityCreatedEvent<Project> event) { ... }
When launching the server Weld tells me it can't handle generic-typed events. The CDI-way of doing things would be to use additional qualifiers instead of the generics to distiguish them, e.g.:
public void handleProjectCreated(@Observes @ProjectEvent EntityCreatedEvent event) { ... }
However, I fire the events from that MyHome base class, where I can't just fire with the @ProjectEvent: it might not be a project but another type.

My solution up to now is to skip that typing altogether and handle them like this:
public void handleProjectCreated(@Observes EntityCreatedEvent event) { 
    if(event.target instanceof Project) { ... }
}
This solution is okay, but not perfect.
解决方案
I guess you can do this with dinamically binding qualifier members. This is what your code would look like:
public abstract class MyHome {

    private EntityType entity;

    @Inject
    Event<EntityCreatedEvent> entityCreatedEvent;

    public void fireCreatedEvent() {
        entityCreatedEvent.select(getTypeBinding()).fire(new EntityCreatedEvent(entity));
    }

    private TypeBinding getTypeBinding() {
        return new TypeBinding() {
        public Class<? extends EntityType> value() {return entity.getClass();}
    };
}

@Qualifier
@Target({ PARAMETER, FIELD })
@Retention(RUNTIME)
public @interface EntityTypeQualifier {
    Class<? extends EntityType> value();
}

public abstract class TypeBinding extends AnnotationLiteral<EntityTypeQualifier> implements EntityTypeQualifier {}

//Observers
public void handleEntityType1Created(@Observes @EntityTypeQualifier(EntityType1.class) EntityCreatedEvent event) {}
public void handleEntityType2Created(@Observes @EntityTypeQualifier(EntityType2.class) EntityCreatedEvent event) {}


                        
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