JAVA：RMI回调 – >对象已导出
这是我的第一个问题，很抱歉，如果我说错了，我的英语。
我必须在java中做一个分布式挂起项目，有客人，玩家和主人（更多匹配）。 当用户（已经注册）自己登录或主人打开比赛时，服务器必须通知所有客人（仅限客人）该事件。 在客户端我必须创建2个存根，1为服务器，另一个为图形界面（swing）。
线程池用于管理匹配，现在不使用。 这是客户端代码：
package User; public class Utente extends RemoteServer implements UserInterface, GraphicInterface,Serializable { private static final long serialVersionUID = 2L; private String name; private String password; private String host = "localhost"; private Socket soc; private int port = 1800; private UserInterface stub = null; private RegistryInterface server_interface = null; private Registry server_registry; public Utente(){ super(); this.name = "user"; this.password = "passwd"; //per connettersi al server try { server_registry = LocateRegistry.getRegistry(host); server_interface = (RegistryInterface)server_registry.lookup("HANGMAN-SERVER"); } catch (RemoteException | NotBoundException e) { System.out.println("errore connessione lato client"); e.printStackTrace(); } //per l' rmi con la gui } public synchronized boolean login(String n, String p) throws RemoteException { boolean esito = false; export(); esito = server_interface.login(n,p,stub); return esito; } public synchronized boolean logout() throws RemoteException { boolean esito = false; esito = server_interface.logout(name,stub); return esito; } public synchronized void notifyMatch(ArrayList lista_partite) throws RemoteException { if(lista_partite!=null){ if(lista_partite.size()==0){ System.out.println("Ancora nessuna partita aperta."); } else{ for(int i = 0;i<lista_partite.size();i++){ System.out.println(lista_partite.get(i).getNameMatch()); } } } } public void connect(){ try { soc = new Socket(host, port); } catch (UnknownHostException e1) { e1.printStackTrace(); } catch (IOException e1) { e1.printStackTrace(); } } public static void main(String[] args) { Utente user = new Utente(); Registry c; GraphicInterface stubExport = null; try{ stubExport = (GraphicInterface)UnicastRemoteObject.exportObject(user,3900); LocateRegistry.createRegistry(5000); c=LocateRegistry.getRegistry(); c.rebind("GraphicUI", stubExport); } catch (RemoteException e) { System.out.println("errore nel client: " + e.toString()); } MainPanel startPanel = new MainPanel(); startPanel.setVisible(true); } } 错误列表：
UI export problems java.rmi.server.ExportException: object already exported at sun.rmi.transport.ObjectTable.putTarget(Unknown Source) at sun.rmi.transport.Transport.exportObject(Unknown Source) at sun.rmi.transport.tcp.TCPTransport.exportObject(Unknown Source) at sun.rmi.transport.tcp.TCPEndpoint.exportObject(Unknown Source) at sun.rmi.transport.LiveRef.exportObject(Unknown Source) at sun.rmi.server.UnicastServerRef.exportObject(Unknown Source) at java.rmi.server.UnicastRemoteObject.exportObject(Unknown Source) at java.rmi.server.UnicastRemoteObject.exportObject(Unknown Source) at User.Utente.export(Utente.java:59) at User.Utente.login(Utente.java:100) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source) at sun.rmi.transport.Transport$1.run(Unknown Source) at sun.rmi.transport.Transport$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.Transport.serviceCall(Unknown Source) at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$254(Unknown Source) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$1/1989325584.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at registry.Server.callbackClient(Server.java:189) at registry.Server.login(Server.java:201) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source) at sun.rmi.transport.Transport$1.run(Unknown Source) at sun.rmi.transport.Transport$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.Transport.serviceCall(Unknown Source) at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$254(Unknown Source) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$1/1786588690.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(Unknown Source) at sun.rmi.transport.StreamRemoteCall.executeCall(Unknown Source) at sun.rmi.server.UnicastRef.invoke(Unknown Source) at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(Unknown Source) at java.rmi.server.RemoteObjectInvocationHandler.invoke(Unknown Source) at com.sun.proxy.$Proxy0.login(Unknown Source) at User.Utente.login(Utente.java:101) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source) at sun.rmi.transport.Transport$1.run(Unknown Source) at sun.rmi.transport.Transport$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.Transport.serviceCall(Unknown Source) at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$254(Unknown Source) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$1/1989325584.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(Unknown Source) at sun.rmi.transport.StreamRemoteCall.executeCall(Unknown Source) at sun.rmi.server.UnicastRef.invoke(Unknown Source) at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(Unknown Source) at java.rmi.server.RemoteObjectInvocationHandler.invoke(Unknown Source) at com.sun.proxy.$Proxy1.login(Unknown Source) at gui.MainPanel$2.actionPerformed(MainPanel.java:110) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.setPressed(Unknown Source) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) at java.awt.Component.processMouseEvent(Unknown Source) at javax.swing.JComponent.processMouseEvent(Unknown Source) at java.awt.Component.processEvent(Unknown Source) at java.awt.Container.processEvent(Unknown Source) at java.awt.Component.dispatchEventImpl(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Window.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.EventQueue.dispatchEventImpl(Unknown Source) at java.awt.EventQueue.access$500(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.run(Unknown Source)
感谢您的耐心等待，我希望这个问题能够很好地形成。 代码是丑陋我知道，没多少时间我改变了很多。
可能，我想我在你的Utente课程中发现了错误。 您已在代码中的2个位置导出对象，这会导致java.rmi.server.ExportException:object already exported.
在你的Utente的main（）方法中，你有
stubExport = (GraphicInterface)UnicastRemoteObject.exportObject(user,3900);
其中user是Utente类的对象。
此外，在同一个类的login（）方法中，您调用的是export（）方法，其中包含： –
stub = (UserInterface) UnicastRemoteObject.exportObject(this,0);
在这里， this将与Utente当前的调用对象有关，在这种情况下，该对象将是先前已导出的用户。
因此，您似乎要将对象导出两次，从而导致抛出exception。
请回复是否有帮助。 祝好运！