EJB 3.1 @LocalBean 与无注释 [英] EJB 3.1 @LocalBean vs no annotation

问题描述

我了解本地视图、远程视图和无接口视图之间的区别.我只是不明白无视图"(无注释)和无界面视图有什么区别.还有为什么我应该用 @Local 注释我的界面?如果我完全不注释接口，那有什么区别吗?

解决方案

规则是(凭记忆):

1. Bean 有一个 @LocalBean 注释 -> bean 有一个无接口视图
2. Bean 有一个 @Local 注释 -> Bean 有一个本地视图
3. Bean 有一个 @Remote 注释 -> Bean 有一个远程视图
4. Bean 没有视图注解，而是直接实现了一个带有@Local 注解的接口 -> bean 有一个本地视图
5. Bean没有视图注解，而是直接实现了一个带有@Remote注解的接口-> bean有一个远程视图
6. Bean没有视图注解，而是直接实现了一个没有视图注解的接口-> bean有一个本地视图
7. Bean 没有视图注解，也没有实现接口 -> bean 没有接口视图

因此，使用 @LocalBean 和根本不使用注释都是获得无接口视图的两种方式.如果你只是想要一个无接口的视图，那么最简单的事情就是不要注释.前提是您还没有实现任何接口.

@LocalBean 存在的部分原因是为了向也有接口视图的 bean 添加一个无接口视图.我想在规范作者的脑海中最重要的场景是你有一个像这样的 bean:

@Stateless公共类用户偏好{公共字符串 getPreference(字符串首选项名称)；公共地图<字符串，字符串>获取首选项()；}

您希望在本地公开两种方法，但仅远程公开粗粒度的 getPreferences().您可以通过仅使用该方法声明远程接口，然后在 bean 类上添加 @LocalBean 来实现.没有它，您就必须编写一个毫无意义的本地接口来在本地公开这两种方法.

或者，换个角度来看，@LocalBean 的存在是因为存在无接口视图这样的东西，而无注释选项作为一种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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