Re: Sporadic ClassCastException

Have you tried setting an uncaught exception handler?

You can use gwt-log (http://code.google.com/p/gwt-log/) to do this:

   public void onModuleLoad() {
      Log.setUncaughtExceptionHandler();
  
    DeferredCommand.addCommand(new Command() {
        public void execute() {
          onModuleLoad2();
      }
      });
  }
  
  private void onModuleLoad2() {
      // Your client code goes here
  }

Or, you can use this rudimentary approach:

   public void onModuleLoad() {
      // set uncaught exception handler
    GWT.setUncaughtExceptionHandler(new GWT.UncaughtExceptionHandler() {
        public void onUncaughtException(Throwable throwable) {
          String text = "Uncaught exception: ";
          while (throwable != null) {
            StackTraceElement[] stackTraceElements = throwable.getStackTrace();
            text += throwable.toString() + "\n";
            for (int i = 0; i < stackTraceElements.length; i++) {
              text += "    at " + stackTraceElements[i] + "\n";
            }
          throwable = throwable.getCause();
            if (throwable != null) {
              text += "Caused by: ";
            }
        }
          DialogBox dialogBox = new DialogBox(true, false);
          DOM.setStyleAttribute(dialogBox.getElement(), "backgroundColor", "#ABCDEF");
          System.err.print(text);
          text = text.replaceAll(" ", "&nbsp;");
          dialogBox.setHTML("<pre>" + text + "</pre>");
          dialogBox.center();
        }
    });
  
    // use a deferred command so that the handler catches onModuleLoad2() exceptions
    DeferredCommand.addCommand(new Command() {
        public void execute() {
          onModuleLoad2();
      }
      });
  }
  
  private void onModuleLoad2() {

      // .....

   }

Fred

On Mon, Oct 25, 2010 at 2:14 AM, Carl <carl@rahmstrom.com> wrote:

Hi, I sporadically receive the exception shown below or simular. This
is in development mode. I'm not sure about production mode. Is there a
way to catch all exceptions in GWT?

I don't see any of my lines in the exception and wonder what I can do
to avoid this in the future.

I use GWT 2.0.4, OS X 10.6.4 and Safari 5.0.2.

java.lang.ClassCastException: null
   at java.lang.Class.cast(Class.java:2990)
   at com.google.gwt.dev.shell.JsValueGlue.get(JsValueGlue.java:166)
   at
com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:57)
   at
com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:
157)
   at
com.google.gwt.dev.shell.BrowserChannel.reactToMessagesWhileWaitingForReturn(BrowserChannel.java:
1714)
   at
com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:
165)
   at
com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:
120)
   at
com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:
507)
   at
com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:
264)
   at
com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:
91)

   at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
   at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:188)

   at sun.reflect.GeneratedMethodAccessor95.invoke(Unknown Source)

   at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:
25)
   at java.lang.reflect.Method.invoke(Method.java:597)
   at
com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
   at
com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
   at
com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:
157)
   at
com.google.gwt.dev.shell.BrowserChannel.reactToMessages(BrowserChannel.java:
1669)
   at
com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:
401)
   at
com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:
222)

   at java.lang.Thread.run(Thread.java:680)

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Fred Sauer

Developer Advocate

Google Inc.

1600 Amphitheatre Parkway

Mountain View, CA 94043
fredsa@google.com

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