从OS X Applet调用java.awt.Toolkit.getDefaultToolkit（）时，空指针异常

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 .

Answer 1

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.