endorsed dir mechanism not working?

Question

I need to debug something happening inside JDK 1.8 classes. I'm trying to use the endorsed dir mechanism mentioned here, but doesn't seem to be working for me. This is what I did (on Windows):

1. copied the javax.swing.plaf.basic.BasicListUI class source code into <JDK_HOME>/jre/lib/endorsed/javax/swing/plaf/basic/

2. Modified the class code, adding:

   static {
       System.out.println("REPLACED BasicListUI");
   }
   

   I expect this to cause the message to be printed as soon as the class is loaded.

3. cd to <JDK_HOME>/jre/lib/endorsed and run javac javax/swing/plaf/basic/BasicListUI. This results in the BasicListUI.class file generated in the same dir as the source file.

4. wrote, and compiled this program:

   import javax.swing.plaf.basic.BasicListUI;
   public class t {
       public static void main(String args[]) {
           System.out.println(System.getProperty("java.endorsed.dirs"));
           System.out.println(BasicListUI.class.getResource("BasicListUI.class"));
       }
   }
   

5. executed program with java t. I don't see the REPLACED BasicListUI message, and the output of the program is:

   C:\Program Files\Java\jdk1.8.0_40\jre\lib\endorsed
   jar:file:/C:/Program%20Files/Java/jdk1.8.0_40/jre/lib/rt.jar!/javax/swing/plaf/basic/BasicListUI.class
   

Also, if I run:

$ java -verbose t | grep BasicListUI

The output is:

[Loaded javax.swing.plaf.basic.BasicListUI from C:\Program Files\Java\jdk1.8.0_40\jre\lib\rt.jar] jar:file:/C:/Program%20Files/Java/jdk1.8.0_40/jre/lib/rt.jar!/javax/swing    /plaf/basic/BasicListUI.class

What am I missing?

Answer 1

Ah, found the problem. The classes have to be packaged in a jar file. so, added

6. jar cvf rt.jar javax/swing/plaf/basic/BasicListUI.class