[Norm]

Can you explain what the objective of your code is?
Here's simple code to replace the %20 with a blank.
Your code already does it. I don't understand what the regex if for.

Code:

// Find path to class file (w/o %20)

import java.net.URLDecoder;


public class FindPathToFile {

   public static void main(String[] args) {
      try {
         new FindPathToFile();
      }catch(Exception x){x.printStackTrace();}
   }

    private final static String Percent = "%";

   public FindPathToFile() throws Exception {
      // Okay, this should be our name.
      String string = this.getClass().getName();
      string.replaceAll("\\.", "/");
      System.out.println("string=" + string + ", user.dir=" + System.getProperty("user.dir"));
      StringBuffer sb = new StringBuffer();

      // Normal sanity check.
      if(string != null)      {
         //
         sb.append(/*FileDog.*/this.getClass().getResource("/" + string + ".class"));
         java.net.URL url= new java.net.URL(sb.toString());
         System.out.println("url=" + url);

         String URLStr = url.toString();
         if(URLStr.indexOf(Percent) >= 0) {
            URLStr = URLDecoder.decode(URLStr, "UTF8");
            System.out.println("decode= " + URLStr);
         }


         //
         java.util.regex.Pattern pitterPatter 
           = java.util.regex.Pattern.compile("file:(/|\\w|\\d|-|_|\\.|!|~|\\*|\'|\\(|\\))+WEB-INF/");//
         //
         String dfltCS = new String(java.nio.charset.Charset.defaultCharset().toString());
         System.out.println("defaultCS="  + dfltCS); //1252
         String decodedURL = new String(java.net.URLDecoder.decode(url.toExternalForm(), dfltCS));
         System.out.println("decode2=" + decodedURL);
         /****** here we go...  ******/
         java.util.regex.Matcher mtchr = pitterPatter.matcher(decodedURL);
         // If we captured state of where we are at ....
         while(mtchr.find())       {
            //
            sb.append(mtchr.group());
//            isValid=Boolean.valueOf(true);//
          }
       System.out.println( sb.toString());//
      }
      
     // prints: file:/C:/Documents%20and%20Settings/Owner/.Arachnophilia/CustomClasses/FileDog.class

   } // end main
} // end class

/*   Output from above
Running: D:\Java\jre6_10\bin\java.exe -classpath D:\JavaDevelopment;. -Xmx128M FindPathToFile

string=FindPathToFile, user.dir=D:\JavaDevelopment\Testing\JavaForum\Folder with blanks
url=file:/D:/JavaDevelopment/Testing/JavaForum/Folder%20with%20blanks/FindPathToFile.class
decode= file:/D:/JavaDevelopment/Testing/JavaForum/Folder with blanks/FindPathToFile.class
defaultCS=windows-1252
decode2=file:/D:/JavaDevelopment/Testing/JavaForum/Folder with blanks/FindPathToFile.class
file:/D:/JavaDevelopment/Testing/JavaForum/Folder%20with%20blanks/FindPathToFile.class

0 error(s)
*/