EJB 3.1 @LocalBean vs no annotation [英] EJB 3.1 @LocalBean vs no annotation

问题描述

我了解本地视图，远程视图和无界面视图之间的区别。我只是不明白无视图（无注释）和无界面视图之间的区别是什么。还有为什么要用 @Local 注释我的界面？如果我没有注释接口，有什么区别吗？

解决方案

规则是（从内存） ：

1. Bean有一个 @LocalBean 注释 - > bean有一个无界面查看


2. Bean有一个 @Local 注释 - > bean有本地视图


3. Bean有一个 @Remote 注释 - > bean有一个远程视图


4. Bean没有视图注释，但是直接实现一个接口， @Local注释 - > bean具有本地视图


5. Bean没有视图注释，但是直接实现了一个具有@Remote注释的界面 - > bean具有远程视图


6. Bean没有视图注释，但是直接实现没有视图注释的接口 - > bean具有本地视图


7. Bean没有视图注释，并且不实现接口 - > bean具有无界面视图

所以，使用 @LocalBean 并且根本不使用任何注释都是获取无界面视图的方式。如果你只想要一个无界面的视图，那么最简单的就是不要注释。如果您还没有实现任何接口。

存在原因的一部分原因 @LocalBean 接口视图到一个也有一个接口视图的bean。我想象，规范作者的头脑中最重要的一个场景是一个你拥有如下的bean：

  @Stateless 
 public class UserPreferences {
 public String getPreference（String preferenceName）; 
 public Map< String，String>的getPreferences（）; 
} 
  

您希望在本地公开这两种方法，但只有粗糙度 getPreferences（）远程。您可以通过仅使用该方法声明远程接口，然后在bean类上轻敲 @LocalBean 来实现。没有它，你必须写一个无意义的本地界面，只是为了在本地公开这两种方法。

或者，另外看看， @LocalBean 存在，因为有一个像无界面视图这样的东西，没有注释选项作为一个方便的快捷方式存在。

I understand the difference between local view, remote view and no-interface view. I just don't understand what is the difference between "no view" (no annotation) and no-interface view. And also why should I annotate my interface with @Local? What if I don't annotate the interface in at all, is there a difference?

解决方案

The rules are (from memory):

1. Bean has a @LocalBean annotation -> bean has a no-interface view
2. Bean has a @Local annotation -> bean has a local view
3. Bean has a @Remote annotation -> bean has a remote view
4. Bean has no view annotations, but directly implements an interface which has a @Local annotation -> bean has a local view
5. Bean has no view annotations, but directly implements an interface which has a @Remote annotation -> bean has a remote view
6. Bean has no view annotations, but directly implements an interface which has no view annotations -> bean has a local view
7. Bean has no view annotations, and implements no interfaces -> bean has a no-interface view

So, using @LocalBean and using no annotation at all are both ways of getting a no-interface view. If you just want a no-interface view, then the simplest thing is not to annotate. Provided you're not also implementing any interfaces.

Part of the reason @LocalBean exists to add a no-interface view to a bean which also has an interface view. I imagine the scenario uppermost in the spec authors' minds was one where you have a bean like:

@Stateless
public class UserPreferences {
    public String getPreference(String preferenceName);
    public Map<String, String> getPreferences();
}

Where you would want to expose both methods locally, but only the coarser-grained getPreferences() remotely. You can do that by declaring a remote interface with just that method, then just slapping @LocalBean on the bean class. Without it, you'd have to write a pointless local interface just to expose both methods locally.

Or, to look at it another way, the @LocalBean exists because there is such a thing as a no-interface view, and the no-annotation option exists as a handy shortcut.

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