使用Java7Update 25的AppContext线程为null

Question

我们最近从更新21更新到Java7Update 25，当从rmi线程调用SwingUtilities.isEventDispatchThread()时，出现了空指针异常，因为AppContext.getAppContext()正在返回null。

.#en2#=‘#en2#1’>( sun.awt.SunToolkit.getSystemEventQueueImplPP(Unknown来源))( sun.awt.SunToolkit.getSystemEventQueueImpl(Unknown来源)在java.awt.Toolkit.getEventQueue(未知来源)在java.awt.EventQueue.isDispatchThread(不明来源)在.(在sun.reflect.NativeMethodAccessorImpl.invoke0(Native ( sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)在java.lang.reflect.Method.invoke(未知来源)在Sun.rmi.transport.transport.rmi.transport.transport$1(未知来源)在sun.rmi.transport.transport.rmi.transport.transport.rmi.transport.transport1.run(未知来源) java.security.AccessController.doPrivileged(Native方法)在sun.rmi.transport.Transport.serviceCall(Unknown源)在sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown源)在sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown源)在sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown源)在java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown源)在java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown源)在java.lang.Thread.run(未知源)

此错误仅在web启动时出现，当我们通过IDE运行应用程序时，它是很好的。

还有其他人碰到这个吗？知道AppContext的最新更新中发生了什么变化吗？

似乎其他人在更新后与AppContext有一些相关的问题：https://forums.oracle.com/message/11077767#11077767

Answer 1

我在运行Java3D时遇到了与相同的问题。我找到了另一个解决办法。您必须准备好自己的InvokeLaterProcessor和可运行的队列。它必须扩展线程和获取ups运行表，并在run方法中处理它们：

public class InvokeLaterProcessor extends Thread {

  private BlockingQueue<Runnable> queue=new ArrayBlockingQueue<Runnable>(1);

  public InvokeLaterProcessor(String name) {
    super(name);
  }

  public void invokeLater(Runnable runnable) {
    try {
      queue.put(runnable);
    } catch (InterruptedException ex) {
      log.warn("invokeLater interrupted");
    }
  }

  public void run() {
    Runnable runnable=null;
    do {
      try {
        runnable = queue.take();
        SwingUtilities.invokeLater(runnable);
      } catch (InterruptedException ex) {
        runnable=null;
      }
    } while(runnable!=null);
  }
}

所要做的就是在某个类的静态中创建它，这个类是在主线程中创建的：

static {
  invokeLaterProcessor=new InvokeLaterProcessor("MyInvokeLater");
  invokeLaterProcessor.start();
}

并通过以下代码处理可运行项：

invokeLaterProcessor.invokeLater(runnable);

你不需要专利

sun.awt.SunToolkit.invokeLaterOnAppContext(evtContext, rn)

Answer 2

这不是一个最终的答案，但它是一个解决办法，对我有效。

应用程序需要将当前的AppContext保存在EVT中：

  AppContext evtContext; //field

  SwingUtilities.invokeLater(new Runnable() {
      public void run() {
          evtContext = AppContext.getAppContext();
      }
  });

然后，必须将来自RMI线程的所有对SwingUtilities.invokeLater(..)的调用替换为使用sun.awt.SunToolkit.invokeLaterOnAppContext(..,..)的自定义invokeLater2(Runnable rn)方法，例如：

void invokeLater2(Runnable rn) {
    if (AppContext.getAppContext() == null) {
        logger.warning("AppContext is null, using EVT AppContext"
          + " through SunToolKit");
        sun.awt.SunToolkit.invokeLaterOnAppContext(evtContext, rn);
    } else {
        SwingUtilities.invokeLater(rn);
    }
}

不幸的是，所有对SwingUtilities.invokeLater(..)的调用必须替换RMI线程，程序现在依赖于内部的Sun专有API。

我希望Oracle不久将为JRE 1.7.0.u 25提供补丁来解决这个问题。

--这一解决办法是根据guruman在here评论中的建议提出的。

Answer 3

下面是JDK-8019274的一个解决方案，打包在一个实用程序类中。

对我们来说，invokeAndWait()是个大问题。此示例具有invokeLater()的现有修复程序和invokeAndWait()的新修复程序。

备注：

• 你需要jnlp.jar
• 在调用init()之前，先在main()方法中调用invokeLater()！
• 用以下调用替换对invokeLater()和invokeAndWait()的所有调用

(免责声明:这是我们的产品。此解决方案的某些方面可能不适用于您。)

public class JreFix {
    private static String badVersionInfo = null;
    private static AppContext awtEventDispatchContext = null;
    private static AppContext mainThreadContext = null;
    private static Boolean isWebStart = null;
    private static BasicService basicService = null;
    private static IntegrationService integrationService = null;

    /**
     * Call this early in main().  
     */
    public static void init() {
        if (isWebstart() && isApplicableJvmType()) {
            String javaVersion = System.getProperty("java.version");

            if ("1.7.0_25".equals(javaVersion)) {
                badVersionInfo = "7u25";
            }
            else if ("1.7.0_40".equals(javaVersion)) {
                badVersionInfo = "7u40";
            }
            else if (javaVersion != null && "1.6.0_51".equals(javaVersion.substring(0,8))) {
                badVersionInfo = "6u51";
            }
            else if ("javaws-10.25.2.16".equals(System.getProperty("javawebstart.version"))) {
                badVersionInfo = "Web Start 10.25.2.16";
            }
        }

        if (badVersionInfo != null) {
            mainThreadContext = AppContext.getAppContext();
            try {
                SwingUtilities.invokeAndWait(new Runnable() {
                    public void run() {
                        awtEventDispatchContext = AppContext.getAppContext();
                    }
                });
            }
            catch (Exception e) {
                displayErrorAndExit(null);
            }

            if (mainThreadContext == null || awtEventDispatchContext == null) {
                 displayErrorAndExit(null);
            }
        }
    }

    public static void invokeNowOrLater(Runnable runnable) {
        if (hasAppContextBug()) {
            invokeLaterOnAwtEventDispatchThreadContext(runnable);
        }
        else {
            SwingUtilities.invokeLater(runnable);
        }
    }

    public static void invokeNowOrWait(Runnable runnable) {
        if (hasAppContextBug()) {
            fixThreadAppContext(null);
        }

        try {
            SwingUtilities.invokeAndWait(runnable);
        } 
        catch (Exception e) {
            // handle it
        }
    }

    public static boolean hasAppContextBug() {
        return isJreWithAppContextBug() && AppContext.getAppContext() == null;
    }

    public static void invokeLaterOnAwtEventDispatchThreadContext(Runnable runnable) {
        sun.awt.SunToolkit.invokeLaterOnAppContext(awtEventDispatchContext, runnable);
    }

    public static void fixThreadAppContext(Component parent) {
        try {
            final Field field = AppContext.class.getDeclaredField("threadGroup2appContext");
            field.setAccessible(true);
            Map<ThreadGroup, AppContext> threadGroup2appContext = (Map<ThreadGroup, AppContext>)field.get(null);
            final ThreadGroup currentThreadGroup = Thread.currentThread().getThreadGroup();
            threadGroup2appContext.put(currentThreadGroup, mainThreadContext);
        } 
        catch (Exception e) {
            displayErrorAndExit(parent);
        }

        if (AppContext.getAppContext() == null) {
             displayErrorAndExit(parent);
        }
    }

    private static boolean isJreWithAppContextBug() {
        return badVersionInfo != null;
    }

    private static void displayErrorAndExit(Component parent) {
        JLabel msgLabel = new JLabel("<html>" + 
                "Our application cannot run using <b>Web Start</b> with this version of Java.<p><p>" +
                "Java " + badVersionInfo + " contains a bug acknowledged by Oracle (JDK-8019274).");
        JOptionPane.showMessageDialog(parent, msgLabel, "Java Version Error", JOptionPane.ERROR_MESSAGE);
        System.exit(1);
    }

    private static boolean isApplicableJvmType() {
        String vendor = System.getProperty("java.vendor");
        String vmName = System.getProperty("java.vm.name");
        if (vendor != null && vmName != null) {
            return vmName.contains("Java HotSpot") &&
                    (vendor.equals("Oracle Corporation") || 
                     vendor.equals("Sun Microsystems Inc."));
        }

        return false;
    }

    private static boolean isWebstart() {
        if (isWebStart == null) {
            try { 
                basicService = (BasicService) ServiceManager.lookup("javax.jnlp.BasicService");             
                isWebStart = true;
            } 
            catch (UnavailableServiceException e) { 
                isWebStart = false;
            }           

            try {
                integrationService = (IntegrationService) ServiceManager.lookup("javax.jnlp.IntegrationService");
            } 
            catch (UnavailableServiceException e) {
            }
        }
        return isWebStart;
    }
}