Servlet 从远程 EJB3 会话 Bean 接收空对象
我确信这是一个初学者错误...
所以我有一个 Java EE 6 应用程序，其中包含实体、外观（实现持久层）和带有远程接口（通过外观提供对实体的访问）的无状态会话 Bean (EJB3)。
这工作正常。通过 SLSB，我可以检索和操作实体。
现在，我尝试从 Web 应用程序执行此操作（部署在同一个 Glassfish 上，来自 Java EE 应用程序的实体+接口定义作为单独的 jar 导入）。我有一个 Servlet，它接收注入的 SLSB 实例。我让它检索一个实体，然后发生以下情况（我可以在日志中看到它）：
- 远程 SLSB 被实例化，其名为
- SLSB 的方法实例化外观，调用“get”方法
- 外观从数据库检索实体实例，返回它
- SLSB 将实体的实例返回给调用者
- （在此之前一切都很好）
- 调用servlet接收..实体的空实例！
出了什么问题？这应该有效，对吧？
MyServlet：
public class MyServlet extends HttpServlet {
@EJB
private CampaignControllerRemote campaignController; // remote SLSB
protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/plain");
PrintWriter out = response.getWriter();
try {
Campaign c = campaignController.getCampaign(5L); // id of an existing campaign
out.println("Got "+ c.getSomeString()); // is null !!
} finally {
out.close();
}
}
...
}
如果您想查看其他代码，请告诉我，我会更新帖子。
I'm sure this is a beginner error...
So I have a Java EE 6 application with entities, facades (implementing the persistence layer) and Stateless Session Beans (EJB3) with Remote interfaces (providing access to the entities via facades).
This is working fine. Via the SLSB I can retrieve and manipulate entities.
Now, I'm trying to do this from a Web Application (deployed on the same Glassfish, entity+interface definitions from Java EE app imported as separate jar). I have a Servlet, that receives an instance of the SLSB injected. I get it to retrieve an entity, and the following happens (I can see it in the logs):
- the remote SLSB gets instantiated, its method called
- SLSB instantiates the facade, calls the 'get' method
- facade retrieves instance of entity from DB, returns it
- SLSB returns the instance of the entity to the caller
- (all is good until here)
- calling servlet receives .. an empty instance of the entity !!
What is going wrong? This should work, right?
MyServlet:
public class MyServlet extends HttpServlet {
@EJB
private CampaignControllerRemote campaignController; // remote SLSB
protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/plain");
PrintWriter out = response.getWriter();
try {
Campaign c = campaignController.getCampaign(5L); // id of an existing campaign
out.println("Got "+ c.getSomeString()); // is null !!
} finally {
out.close();
}
}
...
}
Pls let me know if you want to see other code, and I'll update the post.
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...天哪，这有点尴尬...
事实证明，我一直忽略了一个关于使用
Vector作为包含@ 的字段类型的漂亮小警告xxToMany与 FetchType.LAZY 的关系：两种可能的解决方案可以修复我的行为：
FetchType.EAGER（然后我可以继续使用Vector）List（正如规范所说...... .)... oh boy, this is sort of embarrassing ...
It turns out, I have been ignoring a nice little warning regarding the use of
Vectoras type of a field that holds a@xxToManyrelationship withFetchType.LAZY:Two possible solutions can fix my behaviour:
FetchType.EAGER(then I could stay withVector)List(as the spec says...)