Null Pointer Exception when calling java.awt.Toolkit.getDefaultToolkit() from OS X Applet

Question

I'm getting the following NPE when trying to view a Java applet on OS X 10.7.5:

[2014-04-07T11:39:22.035] [thread applet-com.OTHERCOMPANY.wave.applets.PRODUCT.PRODUCT.class-2] com.COMPANY.nm.logging.LogMaster.auditLoggingMessage AUDIT: HEMXL0001A=Audit logging is enabled.
Exception in thread "AWT-EventQueue-2" java.lang.NullPointerException
    at com.COMPANY.XYZ.applets.PRODUCT.ui.table.TableMouseListener.<init>(TableMouseListener.java:71)
    at com.COMPANY.XYZ.applets.PRODUCT.PRODUCTTable.<init>(PRODUCTTable.java:315)

I do not have the source but assume to have found TableMouseListener.java:71 using javap:

  public com.COMPANY.XYZ.applets.PRODUCT.ui.table.TableMouseListener(com.COMPANY.XYZ.applets.PRODUCT.PRODUCTContext, javax.swing.JTable);
    flags: ACC_PUBLIC
    Code:
      stack=5, locals=4, args_size=3
         0: aload_0       
         1: invokespecial #1                  // Method com/OTHERCOMPANY/wave/uicomponents/PopupListener."<init>":()V
         4: aload_0       
         5: aconst_null   
         6: putfield      #2                  // Field firstClickEvent:Ljava/awt/event/MouseEvent;
         9: aload_0       
        10: aload_1       
        11: putfield      #3                  // Field context:Lcom/COMPANY/XYZ/applets/PRODUCT/PRODUCTContext;
        14: aload_0       
        15: aload_2       
        16: putfield      #4                  // Field table:Ljavax/swing/JTable;
THIS  --->    
        19: invokestatic  #5                  // Method java/awt/Toolkit.getDefaultToolkit:()Ljava/awt/Toolkit;
        22: ldc           #6                  // String awt.multiClickInterval
        24: invokevirtual #7                  // Method java/awt/Toolkit.getDesktopProperty:(Ljava/lang/String;)Ljava/lang/Object;
        27: checkcast     #8                  // class java/lang/Integer
        30: invokevirtual #9                  // Method java/lang/Integer.intValue:()I
        33: istore_3      
        34: aload_0       
THIS  --->    
        35: new           #10                 // class javax/swing/Timer
        38: dup           
        39: iload_3       
        40: aload_0       
        41: invokespecial #11                 // Method javax/swing/Timer."<init>":(ILjava/awt/event/ActionListener;)V
        44: putfield      #12                 // Field clickTimer:Ljavax/swing/Timer;
        47: return        
      LineNumberTable:
        line 65: 0
        line 62: 4
        line 66: 9
        line 67: 14
        line 71: 19
        line 72: 34
        line 73: 47

Any good ideas what might cause this and what could be a workaround? I'm not exactly clear on what this toolkit does but it seems to provide an interface to the graphics system which might be restricted from the applet sandbox?

Some stuff I have investigated:

this did not happen with an older version of the applet that did not call getDefaultToolkit()
this seems only to happen on OS X, Windows and Linux are fine
I have tried the medium applet security setting, deleting the Java cache and some other voodoo to no avail
Generally calling this method outside of an applet works fine, see below.

$ cat gettk.java 
import java.awt.*;

public class gettk {
    public static void main(String args[]) throws Exception {
        System.out.println("tk = " + Toolkit.getDefaultToolkit());
    }
}
$ java gettk
tk = sun.lwawt.macosx.LWCToolkit@32d16dc8

Update I: as suggested by a comment, here's a nicer decompile. Line 71 is:

 int multiClickInterval = ((Integer)Toolkit.getDefaultToolkit().getDesktopProperty("awt.multiClickInterval")).intValue();

Turns out the problem might very well be the usage of awt.multiClickInterval. I'll check if I can shoehorn this in from <embed> properties.

Update II:

Yes the missing awt.multiClickInterval is the issue:

rc@ds9000:~ $ cat gettk.java 
import java.awt.*;

public class gettk {
    public static void main(String args[]) throws Exception {
        System.out.println("tk = " + Toolkit.getDefaultToolkit());
    int multiClickInterval = ((Integer)Toolkit.getDefaultToolkit().getDesktopProperty("awt.multiClickInterval")).intValue();
    System.out.println(multiClickInterval);
    }
}
rc@ds9000:~ $ java gettk
tk = sun.lwawt.macosx.LWCToolkit@15e6e48b
Exception in thread "main" java.lang.NullPointerException
    at gettk.main(gettk.java:6)

Unfortunately I seem to be unable to pass it as system property:

rc@ds9000:~ $ java -Dawt.multiClickInterval=200 gettk 
tk = sun.lwawt.macosx.LWCToolkit@15e6e48b
Exception in thread "main" java.lang.NullPointerException
    at gettk.main(gettk.java:6)

Wierdly enough there is a note on how this was fixed in OS X 10.5 here (by Apple?), but also multiple instances of WONTFIX for Java 7 and 8 in the upstream JDK Jira here.

There are several java decompilers out there. They aren't perfect, but at least they make human readable code. Please use one and edit your question. Try jd.benow.ca — DankMemes
Thanks, updated. the awt.multiClickInterval query might be the problem — C. Ramseyer
Yes, I think so too. Try running the program on the command line with -Dawt.multiClickInterval=200 (or whatever your OS multi click interval is) — DankMemes
Seems really to be the issue. Unfortunately this property doesn't seem to be settable from -D system properties, see pastes above. Looks like I need to find another way to get this in. — C. Ramseyer

DankMemes DankMemes · Accepted Answer · 2014-04-08T19:14:35

Aha. I found a fix for you. It requires some hacks though.

public class HackApplet extends WhateverRandomAppletClassItWas {
    public void init(){
         Toolkit.getDefaultToolkit().setDesktopProperty("awt.multiClickInterval", 200);
         super.init();
    }
}

Then just get rid of the actual applet's signature (if any), add you custom applet in, manually sign (otherwise I'm sure setDesktopProperty isn't going to work), and it should work.

Null Pointer Exception when calling java.awt.Toolkit.getDefaultToolkit() from OS X Applet

1 Answers