JDK-8150800 : NullPointer exception in WebView
  • Type: Bug
  • Component: javafx
  • Sub-Component: web
  • Affected Version: 8u73,9
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • OS: windows_7
  • CPU: x86_64
  • Submitted: 2016-02-27
  • Updated: 2016-05-10
  • Resolved: 2016-05-10
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JDK 8 JDK 9
8u112Fixed 9Fixed
Description
FULL PRODUCT VERSION :
java version "1.8.0_73"
Java(TM) SE Runtime Environment (build 1.8.0_73-b02)
Java HotSpot(TM) 64-Bit Server VM (build 25.73-b02, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.1.7601]

A DESCRIPTION OF THE PROBLEM :
Unfortunately I did not succeed in reproducing this exception. It occured only once and the stack trace indicates that only internal javafx  libraries are involved. The exception is the following:

java.lang.NullPointerException
	at javafx.scene.web.WebView.processMouseEvent(WebView.java:1005)
	at javafx.scene.web.WebView.lambda$registerEventHandlers$32(WebView.java:1144)
	at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
	at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
	at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
	at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
	at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
	at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
	at javafx.event.Event.fireEvent(Event.java:198)
	at com.sun.javafx.event.EventQueue.fire(EventQueue.java:48)
	at javafx.scene.Scene$MouseHandler.handleEnterExit(Scene.java:3676)
	at javafx.scene.Scene$MouseHandler.process(Scene.java:3742)
	at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
	at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
	at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
	at java.security.AccessController.doPrivileged(Native Method)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:388)
	at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
	at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
	at com.sun.glass.ui.View.notifyMouse(View.java:937)
	at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
	at java.lang.Thread.run(Thread.java:745)

I have a MOUSE_EXITED event defined on the webivew, which simplified looks like:

  webView.setOnMouseExited((event) -> {
           Element e = webView.getEngine().getDocument().getDocumentElement();
           e.setAttribute("style", "background-color: #dedede;");
 });

but this event always worked and also worked, after the exception was thrown.


ERROR MESSAGES/STACK TRACES THAT OCCUR :
java.lang.NullPointerException
	at javafx.scene.web.WebView.processMouseEvent(WebView.java:1005)
	at javafx.scene.web.WebView.lambda$registerEventHandlers$32(WebView.java:1144)
	at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
	at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
	at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
	at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
	at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
	at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
	at javafx.event.Event.fireEvent(Event.java:198)
	at com.sun.javafx.event.EventQueue.fire(EventQueue.java:48)
	at javafx.scene.Scene$MouseHandler.handleEnterExit(Scene.java:3676)
	at javafx.scene.Scene$MouseHandler.process(Scene.java:3742)
	at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
	at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
	at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
	at java.security.AccessController.doPrivileged(Native Method)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:388)
	at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
	at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
	at com.sun.glass.ui.View.notifyMouse(View.java:937)
	at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
	at java.lang.Thread.run(Thread.java:745)

REPRODUCIBILITY :
This bug can be reproduced rarely.
Comments
Changeset: 6618e541bac7 Author: mbilla Date: 2016-05-10 11:40 +0530 URL: http://hg.openjdk.java.net/openjfx/9-dev/rt/rev/6618e541bac7
10-05-2016
I would add that normally we would not make such a change without a test case that reproduces the bug and that we can use to verify the fix. However, in this case we clearly will get an NPE if the mouse event is processed after the window or scene goes to null, so the null check is a very safe and effective fix.
09-05-2016
+1
09-05-2016
webrev: http://cr.openjdk.java.net/~mbilla/8150800/webrev.00/ As per discussion with kevin, Fix provided based on call stack information as there is no test case available to reproduce this NPE. Checked the call stack with Fx 8u71 code @ javafx.scene.web.WebView.processMouseEvent(WebView.java:1005). private void processMouseEvent(MouseEvent ev) { 1004 Point2D screenPoint = localToScreen(x, y); 1005 screenX = screenPoint.getX(); 1006 screenY = screenPoint.getY(); } Exception points to screenPoint being null. I checked localToScreen() which returns null in case of scene or window is null. public Point2D localToScreen(double localX, double localY, double localZ) { Scene scene = getScene(); if (scene == null) return null; Window window = scene.getWindow(); if (window == null) return null; ........................................ ............................................. }
09-05-2016