If I have a file structure
/core/ (here is application)
/core/doc ( here is the doc )
/core/doc/filecollection1/
/core/doc/filecollection1/subcollection1/
/core/doc/filecollection1/subcollection2/
/core/doc/filecollection2/
/core/doc/filecollection2/subcollection1/
/core/doc/filecollection2/subcollection2/

I compress the application and doc in the jar file.
I want to access to every dir or file recursively.

How to write my code?

PS:
I have written the code
...

   File codebase = new File("/core/doc");
...
   public String read_file_recursive( File file)
   {
       String ret;
       if( codebase.isDirectory())
       {
           File[] filelist = codebase.listFiles();
           for( int i = 0 ; i < filelist;i++ )
           {
               ret += read_file_recursive(filelist[i]);
           }
       }
       else
       {
           // read file content ...
       }
       return ret;
   }
...
But it doesn't work in the jar file.

I guess that the problem occur at the concept of package or directory in the
jar file.