EJB 问题 - 有状态会话 Bean 和 Servlet

Question

我有一个 servlet 代码，它调用 ejb 有状态会话 bean 代码，如下所示，

public class UsesBeansSF extends HttpServlet {   
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
    try {
          // do something
       }

    finally {}
 } 

private SessionBeanSFRemote lookupSessionBeanSFRemote() {
    try {
        Context c = new InitialContext();
        return (SessionBeanSFRemote) c.lookup("java:global/MyEJBSF/SessionBeanSF!ejbSF.SessionBeanSFRemote");
    } catch (NamingException ne) {
        Logger.getLogger(getClass().getName()).log(Level.SEVERE, "exception caught", ne);
        throw new RuntimeException(ne);
    }
}

}

该代码在没有 * 标记之间的情况下运行良好。但是，当我添加 SessionBeanSFRemote sessionBeanSF = LookupSessionBeanSFRemote() 这行（意味着调用有状态会话 Bean）时，代码给出错误。实际上，我必须调用无状态会话 bean 才能执行某些工作。谁能帮助我为什么会发生这种情况？提前致谢。

错误消息如下：

类型异常报告消息

descriptionThe server encountered an internal error () that prevented it from fulfilling this request.

异常

javax.servlet.ServletException: PWC1392: Error instantiating servlet class websSF.comsSF.UsesBeansSF

根本原因

com.sun.enterprise.container.common.spi.util.InjectionException: 
         Error creating managed object for class websSF.comsSF.UsesBeansSF

根本原因

java.lang.reflect.InvocationTargetException

根本原因 >

java.lang.RuntimeException: javax.naming.NamingException: 
Lookup failed for 'java:global/MyEJBSF/SessionBeanSF!ejbSF.SessionBeanSFRemote' in SerialContext  
[Root exception is javax.naming.NamingException: 
ejb ref resolution error for remote business interfaceejbSF.SessionBeanSFRemote [Root exception is java.lang.NullPointerException]]

根本原因

javax.naming.NamingException: 
Lookup failed for 'java:global/MyEJBSF/SessionBeanSF!ejbSF.SessionBeanSFRemote' in SerialContext  
[Root exception is javax.naming.NamingException: 
ejb ref resolution error for remote business interfaceejbSF.SessionBeanSFRemote
[Root exception is java.lang.NullPointerException]]

根本原因

javax.naming.NamingException: ejb ref resolution error for remote business 
interfaceejbSF.SessionBeanSFRemote [Root exception is java.lang.NullPointerException]

根本原因

java.lang.NullPointerException
note The full stack traces of the exception and its root causes are available in the GlassFish Server Open Source Edition 3.0.1 logs.

服务器：GlassFish Server 开源版 3.0.1

Answer 1

我不确定您是否已正确设置 Stateful bean。你可以尝试这个：

@Stateful(mappedName = "ejb/myStatefulBean")
public class MyStatefulBean implements MyStatefulRemoteInterface {
   // Your implementation
}

然后你可以用以下命令查找它：

InitialContext context = new InitialContext();
MyStatefulRemoteInterface myStatefulBean = (MyStatefulRemoteInterface) context.lookup("ejb/myStatefulBean");

此外，这个有状态bean应该保存到每个客户端的会话中以供重复使用：

HttpSession clientSession = request.getSession(false);
clientSession.setAttribute("myStatefulBean", myStatefulBean);

在将来的请求中，你可以尝试先从客户端的会话中获取bean，然后再创建一个给他新的。