code: private void collectFiles(final File folder, final List<File> found) {
  		File[] files = folder.listFiles();
  		if (files != null) {
  			for (File file : files) {
  				if (file.isDirectory()) {
  					collectFiles(file, found);
  				} else if (file.isFile() && file.getPath().endsWith(suffix)) {
  					int index = 0;
  
  					for (String text : plainTexts) {
  						index = file.getPath().indexOf(text, index);
  						if (index == -1) {
  							break;
  						} else {
  							index += text.length();
  						}
  					}
  
  					if (index >= 0) {
  						found.add(file);
  					}
  				}
  			}
  		}
  	}
docs: Collects files from a folder and all nested sub folders.
  
  @param folder
  Base folder for starting search
  @param found
  All found files will be added to this list