code: public static File[] getFilesListByExtention( String folderPath, final String ext ) {
          File[] files = new File(folderPath).listFiles(new FilenameFilter(){
              public boolean accept( File dir, String name ) {
                  return name.endsWith(ext);
              }
          });
          return files;
      }
docs: Get the list of files in a folder by its extension.
  
  @param folderPath the folder path.
  @param ext        the extension without the dot.
  
  @return the list of files patching.