通过Java Webstart运行时,invokeLater中出现NullPointerException

Question

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,当它作为一个独立的应用程序(在JWS之外)执行时,它运行良好.

这是堆栈的顶部:

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)
    (...)

为了全面了解:方法setBaseUnits(..)被远程服务器从RMI调用为回调.完整的堆栈跟踪很长.

安全模型中是否有某些内容在RMI或JWS中发生了变化,可能会破坏事物？如果是这样,我会期待一些安全性异常,但它可能是在JRE中未正确检测到的并导致NPE.

任何建议表示赞赏.

---

----更新1 :

JRE 1.7.0_25更新可能存在类似的问题,可能涉及一些安全更改和AppContext对象:https : //forums.oracle.com/message/11080621 https://forums.oracle.com/thread/2552799.我尝试过建议修复:https://forums.oracle.com/message/11082162#11082162但没有任何成功.

我可以在我的应用程序中看到3个AWT-EventQueue线程,数字从0到2.看起来如果JWS启动程序,JRE会为不同的应用程序上下文创建额外的事件队列.JWS中有3个AppContext和3个EVT,如果从IDE执行程序,则只有一个上下文和EVT.

---

----更新2 :

下面的guruman建议有一个解决方法(非常感谢).不幸的是,SwingUtilities.invokeLater(..)必须替换对来自RMI线程的所有调用,并且程序开始依赖于Sun JRE内部API.

我仍然在寻找更具体的方法,而不是针对Sun JRE.我认为这是一个JRE错误.也许它可以以某种方式修补:在RMI线程中AppContext不应为null.

---

----更新3:

我做了一个简单的测试用例来说明问题.它包含4个文件.要运行此测试用例,需要签署目标jar(TestCase.jar).首先在launch.jnlp中指定正确的代码库,然后通过Java Web Start运行服务器(例如,使用javaws launch.jnlp).屏幕上应显示以下框架:

然后可以执行RMI客户端.成功执行后,框架应包括:

但是如果您尝试使用JWS执行服务器您将在客户端程序中获得以下异常(异常从RMI服务器传播到RMI客户端):

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)

所以这里是测试用例文件:

1)JNLP文件定义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接口定义(RmiService.java):

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

3)RMI服务代码和服务主类:

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)简单的客户端代码:

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();
    }
}

---

----更新4:

我提交的JRE Bug:http://bugs.sun.com/bugdatabase/view_bug.do？video_id = 8019272

其他相关错误:

• http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8019274
• http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8028290
• http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8017770
• http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8021370

Answer 1

我找到了我认为更好的解决这个bug的方法.

我在调用SwingUtilities或任何与Swing相关的组件方法之前添加了以下代码.它为RMI线程创建一个新的AppContext(在运行下面的代码时,RMI线程必须是当前的线程).

if(AppContext.getAppContext() == null){
    SunToolkit.createNewAppContext();
}

由于我的应用程序的需要,我能够在使用SwingUtilities的单个方法上添加它,但您可能需要将它添加到RMI可调用对象上的每个方法.

代码只需运行一次,因此请检查应用程序的行为.

Answer 2

Webstart环境中出现此问题.在Webstart版本的Java 7u25之前,在系统线程组上设置了AppContext.然而它是在主线程组上设置的.

如果您有一个基于线程组的线程,其父或祖父不是主线程组,则它没有sun.awt.AppContext.

您应该根据安全管理器的线程组创建线程(如果存在).

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