I tried to use the ClassLoaders in Java but they were a bit complicated for me. Then I download the JSPF lib and integrated it. Though it is working for the plugin you get with lib itself (coolplugin.jar) but I'm not able to create my own plugins. I have tried both Processing as an IDE and used simple Java from other IDEs. 

What I want is to be albe to make plugins compatible with JSPF from Processing only.

Here is come code I have been using to load .jar files and add plugins (it works fine) - 

1. import  java.io.* ;
2. import  java.util.* ;
3. import  java.net.* ;
4. import  java.lang.reflect.* ;
5. import  java.lang.Object.* ;
6. import  net.xeoh.plugins.base.* ;
7.  
8. String AppDir  =  System. getProperty ( "user.home" )
                   + File. separator + "Documents" + File. separator + "VIKI" ;
9.  
10. void setup ( )  {
11.   size  ( 800,  500 ) ;
12.    File dir  =  new  File  (AppDir ) ;
13.   PluginManager pm  = PluginManagerFactory. createPluginManager ( ) ;
14.    if  ( !dir. exists ( ) )  {
15.     println  ( "The new folder is created." ) ;
16.     dir. mkdir ( ) ;
17.    }
18.    String [ ] Child  = getChildFolderNames (AppDir ) ;
19.    for  ( int i  =  0 ; i  <= Child. length - 1 ; i ++ )  {
20.     println  (Child [i ] ) ;
21.    }
22.    for  ( int i  =  0 ; i  <= Child. length - 1 ; i ++ )  {
23.      String Source  = AppDir + File. separator +Child [i ]
                  + File. separator + "App" + File. separator +Child [i ] + ".jar" ;
24.     println  (Source ) ;
25.     pm. addPluginsFrom ( new  File (Source ). toURI ( ) ) ;
26.    }
27. }
28.  
29. void draw ( )  {
30. }
31.  
32. public  String [ ] getChildFolderNames ( String startFolder )  {
33.   List <String > folderNames  =  new ArrayList <String > ( ) ;
34.  
35.    File aFolder  =  new  File (startFolder ) ;
36.    File [ ] allFiles  = aFolder. listFiles ( ) ;
37.    for  ( File f  : allFiles )  {
38.      if  (f. isDirectory ( ) )  {
39.       folderNames. add (f. getName ( ) ) ;
40.      }
41.    }
42.    return  ( String [ ] ) folderNames. toArray ( new  String [ 0 ] ) ;
43. }

Thanks.

http://robocasters.com

at -  XMLElement[] usersXml;

it says - Cannot find a class or type named "XMLElement"

NullPointerException  (at - nxt.resetMotorPosition(1, true);)