Brother you don't need to set class path just follow these simple steps (I use Apache NetBeans)
Steps:
extract the jar file which you want to add in your project.
only copy those packages (folder) which you need in the project. (do not copy manifest file)
open the main project jar file(dist/file.jar) with WinRAR.
paste that folder or package in the main project jar file.
Those packages work 100% in your project.
warning: Do not make any changes in the manifest file.
Another method:
we need to move lib folder in dist folder.then we set class path from manifest.mf file of main jar file.
Edit the manifest.mf And ADD this type of line
Warning: lib folder must be inside the dist folder otherwise jar file do not access your lib folder jar files