通过 Java Webstart 运行时 invokeLater 中的 NullPointerException [英] NullPointerException in invokeLater while running through Java Webstart

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问题描述

从 JRE 1.7.0_21 升级到 1.7.0_25-b15 后，我的应用程序在从 Java WebStart 运行时开始在 SwingUtilities.invokeLater(...) 中抛出 NullPointerException.令人惊讶的是，当它作为独立应用程序(在 JWS 之外)执行时，效果很好.

这是栈顶:

线程AWT-EventQueue-2"中的异常 java.lang.NullPointerException在 sun.awt.SunToolkit.getSystemEventQueueImplPP(SunToolkit.java:1011)在 sun.awt.SunToolkit.getSystemEventQueueImplPP(SunToolkit.java:1007)在 sun.awt.SunToolkit.getSystemEventQueueImpl(SunToolkit.java:1002)在 java.awt.Toolkit.getEventQueue(Toolkit.java:1730)在 java.awt.EventQueue.invokeLater(EventQueue.java:1217)在 javax.swing.SwingUtilities.invokeLater(SwingUtilities.java:1290)在 AppletView$8.setBaseUnits(AppletView.java:536)(...)

为了让您全面了解:方法 setBaseUnits(..) 被远程服务器调用作为来自 RMI 的回调.完整的堆栈跟踪很长.

RMI 或 JWS 中安全模型中的某些更改可能会破坏某些内容吗?如果是这样，我会期待一些安全异常，但它可能是在 JRE 中未正确检测到并导致 NPE 的问题.

感谢任何建议.

<小时>

---- 更新1:

JRE 1.7.0_25 更新存在类似问题，可能与一些安全更改和 AppContext 对象有关:

其他相关错误:

解决方案

问题出现在Webstart环境.在 Java 7u25 的 Webstart 版本之前，AppContext 是在系统线程组上设置的.然而它被设置在主线程组上.

如果您的线程基于其父线程组或祖父线程组不是主线程组，则它没有 sun.awt.AppContext.

您应该根据安全管理器的线程组(如果存在)创建线程.

可运行任务 = ....ThreadGroup threadGroup = System.getSecurityManager() != null?System.getSecurityManager().getThreadGroup(): Thread.currentThread().getThreadGroup();线程 t = new Thread(threadGroup, task, "我的线程", 0);

After upgraded from JRE 1.7.0_21 to 1.7.0_25-b15 my application started to throw NullPointerException in SwingUtilities.invokeLater(...) when it is run from Java WebStart. Surprisingly when it is executed as a standalone application (outside JWS), it works great.

Here is the top of the stack:

Exception in thread "AWT-EventQueue-2" java.lang.NullPointerException
at sun.awt.SunToolkit.getSystemEventQueueImplPP(SunToolkit.java:1011)
at sun.awt.SunToolkit.getSystemEventQueueImplPP(SunToolkit.java:1007)
at sun.awt.SunToolkit.getSystemEventQueueImpl(SunToolkit.java:1002)
at java.awt.Toolkit.getEventQueue(Toolkit.java:1730)
at java.awt.EventQueue.invokeLater(EventQueue.java:1217)
at javax.swing.SwingUtilities.invokeLater(SwingUtilities.java:1290)
at AppletView$8.setBaseUnits(AppletView.java:536)
    (...)

To get you full picture: the method setBaseUnits(..) is called as a callback from RMI by remote server. The full stack trace is quite long.

Is there something in security model that changed in RMI or JWS that could break things ? If so I would expect some security exception, but it could be something that is not correctly detected in JRE and leads to NPE.

Any suggestions are appreciated.

---- Update1:

There are similar issues with JRE 1.7.0_25 update probably regarding some security changes and AppContext objects: https://forums.oracle.com/message/11080621 https://forums.oracle.com/thread/2552799 . I tried suggested fix: https://forums.oracle.com/message/11082162#11082162 but without any success.

I can see 3 AWT-EventQueue threads in my application with numbers from 0 to 2. It looks like JRE creates additional event queues for different application contexts if program is started by JWS. There are 3 AppContext and 3 EVTs in JWS and there is only one context and EVT if program is executed from IDE.

---- Update2:

There is a workaround as suggested by guruman below (thanks a lot). Unfortunately all the calls to the SwingUtilities.invokeLater(..) from RMI threads must be replaced, and the program starts to depend on Sun JRE internal API.

I am still looking for more general approach not specific to Sun JRE. I think it is a JRE bug. Maybe it could be patched somehow: AppContext should not be null in RMI thread.

---- Update3:

I've made a simple test case to show the problem. It consists 4 files. To run this test case one need to sign the destination jar (TestCase.jar). First of all specify correct codebase in launch.jnlp, then run the server by Java Web Start (eg. using javaws launch.jnlp). A following frame should appear on the screen:

Then the RMI client could be executed. After successful execution the frame should consist:

but if You try to execute the server using JWS You will get the following exception in the client program (the exception is propagated from RMI server to RMI client):

Exception in thread "main" java.lang.NullPointerException
    at sun.awt.SunToolkit.getSystemEventQueueImplPP(SunToolkit.java:1011)
    at sun.awt.SunToolkit.getSystemEventQueueImplPP(SunToolkit.java:1007)
    at sun.awt.SunToolkit.getSystemEventQueueImpl(SunToolkit.java:1002)
    at java.awt.Toolkit.getEventQueue(Toolkit.java:1730)
    at java.awt.EventQueue.invokeLater(EventQueue.java:1217)
    at javax.swing.SwingUtilities.invokeLater(SwingUtilities.java:1290)
    at testcase.RmiServiceImpl.callBack(RmiServiceImpl.java:70)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:322)
    at sun.rmi.transport.Transport$1.run(Transport.java:177)
    at sun.rmi.transport.Transport$1.run(Transport.java:174)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
    at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:553)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:808)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:667)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:724)
    at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(StreamRemoteCall.java:273)
    at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:251)
    at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:160)
    at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:194)
    at java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:148)
    at com.sun.proxy.$Proxy0.callBack(Unknown Source)
    at testcase.RmiClient.main(RmiClient.java:22)

So here they are the test case files:

1) JNLP file definition launch.jnlp:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<jnlp codebase="file:/home/user/NetBeansProjects/TestCase/dist/" href="launch.jnlp" spec="1.0+">
    <information>
        <title>TestCase</title>
        <vendor>digital_infinity</vendor>
        <homepage href=""/>
        <description>TestCase</description>
        <description kind="short">TestCase</description>
    </information>
<security>
  <all-permissions/>
</security>
    <update check="always"/>
    <resources>
        <j2se version="1.7+"/>
        <jar href="TestCase.jar" main="true"/>
    </resources>
    <application-desc main-class="testcase.RmiServiceImpl">
    </application-desc>
</jnlp>

2) RMI interface definition (RmiService.java):

package testcase;    
public interface RmiService extends java.rmi.Remote  {
    void callBack() throws java.rmi.RemoteException;
}

3) RMI service code and the service main class:

package testcase;

import java.rmi.RemoteException;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

/**
 */
public class RmiServiceImpl extends java.rmi.server.UnicastRemoteObject 
implements RmiService {

    final static int PORT = 1099;

    static JFrame frame;
    static JTextField textField;

    public RmiServiceImpl() throws RemoteException {
        super(PORT);
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws Exception {
        Registry reg;
        RmiServiceImpl service = new RmiServiceImpl();
        try {
            reg = LocateRegistry.getRegistry(PORT);
            reg.rebind("test", service);
        } catch (RemoteException ex) {
            reg = LocateRegistry.createRegistry(PORT);
            reg.rebind("test", service);
        }
        SwingUtilities.invokeAndWait(new Runnable() {
            @Override
            public void run() {
                frame = new JFrame("Test App");
                textField = new JTextField("Before call to callBack");
                frame.getContentPane().add(textField);
                frame.pack();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setVisible(true);
            }
        });
    }

    /** RMI callback */
    public void callBack() {
        Runnable rn = new Runnable() {
            public void run() {
                textField.setText("CallBack succesfully called.");
                frame.pack();
            }
        };
        SwingUtilities.invokeLater(rn);
    }
}

4) Simple client code:

package testcase;

import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;

public class RmiClient {
    public static void main(String[] args) throws Exception {
        //now we trying to communicate with object through RMI
        Registry reg = LocateRegistry.getRegistry(RmiServiceImpl.PORT);
        //after got the registry, lookup the object and finally do call
        RmiService serv = (RmiService) reg.lookup("test");
        serv.callBack();
    }
}

---- Update4:

JRE Bug I submitted: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8019272

Other related bugs:

解决方案

The problem occurs in the Webstart environment. Before Webstart version of Java 7u25 the AppContext was set on the system thread group. Yet it is set on the main thread group.

If you have a thread based on a thread group where its parent or grandparent is not the main thread group it has no sun.awt.AppContext.

You should create your thread based on the thread group of the security manager if one exists.

Runnable task = ....
ThreadGroup threadGroup = System.getSecurityManager() != null
                                    ? System.getSecurityManager().getThreadGroup()
                                    : Thread.currentThread().getThreadGroup();
Thread t = new Thread(threadGroup, task, "my thread", 0);

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