Lookup返回有状态会话bean的新实例 [英] Lookup returns new instance of Stateful session bean

问题描述

我正在使用 Java EE 5 ， EJB 3.0 ， Jboss AS 4.3.2 。

我最简单有状态 bean

I am using Java EE 5, EJB 3.0, Jboss AS 4.3.2.
I have simplest Stateful bean

@Local
public interface IStateBean 
{
}
@Stateful
public class StateBean implements IStateBean
{  
   private static int number = 0;

   @PostConstruct
   void init()
   {
      number++;
      System.out.println("@PostConstruct: " + number);
   }

   @PreDestroy
   void destroy()
   {
      number--;
      System.out.println("@PreDestroy: " + number);  
   }
}

我在servlet中查找此bean

I do lookup in servlet for this bean

public class MyServlet extends HttpServlet
{  
   @Override
   public void doGet(final HttpServletRequest aRequest, final HttpServletResponse aResponse) throws ServletException, IOException
   {  
      IStateBean bean = new InitialContext().lookup("app-ear/StateBean/local");
      // ...
   }
}  

但每个时间新的 StateBean 实例已创建。

我可以调用 lookup 两次但新实例再次创建 StateBean

But each time new instance of StateBean is created.
I can call lookup twice but new instance of StateBean is created again

   @Override
   public void doGet(final HttpServletRequest aRequest, final HttpServletResponse aResponse) throws ServletException, IOException
   {  
      IStateBean bean1 = new InitialContext().lookup("app-ear/StateBean/local"); 
      IStateBean bean2 = new InitialContext().lookup("app-ear/StateBean/local"); // new instance is created
      // ...
   }  

我希望在同一个http-session中使用相同的实例

web.xml中的Servlet映射

Servlet mapping in web.xml

   <servlet>
      <servlet-name>MyServlet</servlet-name>
      <servlet-class>com.package.MyServlet</servlet-class>
   </servlet>  
   <servlet-mapping>
      <servlet-name>MyServlet</servlet-name>
      <url-pattern>*.html</url-pattern>
   </servlet-mapping>

推荐答案

EJB规范没有说多个查找将会返回有状态会话bean的同一个实例。相反：服务器甚至需要创建两个不同的实例，以保证每个客户端在服务器上获得自己的实例。

The EJB spec does not say, that multiple lookups will return the same instance of a stateful session bean. In opposite: It is even required for the server to create two different instances, to guarantee that every client gets his own instance on the server.

EJB规范只说明了当您引用有状态会话bean时，它会在多个方法调用中保留其内部状态：

The EJB spec only says that while you're referencing a stateful session bean, it retains its internal state across multiple method invocations:

IStateBean bean = new InitialContext().lookup("app-ear/StateBean/local");
bean.myMethod1();
bean.myMethod2(); // affects the same EJB instance on the server

请注意，使用无状态时可能不是这种情况会话bean。在这里，上面显示的两个方法调用可能会转到服务器上的不同实例！

Note that this might NOT be the case when using stateless session beans. Here, the two method calls shown above might go to different instances on the server!

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