code: public static List<String> listAllMime( String directory , String type ) {
  		List<String> ret = new ArrayList<>();
  
  		try {
  			// see if it's a URL or not
  			URL url = new URL(directory);
  			if( url.getProtocol().equals("file") ) {
  				directory = url.getFile();
  			} else if( url.getProtocol().equals("jar") ) {
  				return listJarMime(url,null,null);
  			} else {
  				throw new RuntimeException("Not sure what to do with this url. "+url.toString());
  			}
  		} catch (MalformedURLException ignore) {
  		}
  
  		File d = new File(directory);
  
  		if( !d.isDirectory() )
  			throw new IllegalArgumentException("Must specify an directory");
  
  		File []files = d.listFiles();
  		if( files == null )
  			return ret;
  
  		for( File f : files ) {
  			if( f.isDirectory() )
  				continue;
  			try {
  				String mimeType = Files.probeContentType(f.toPath());
  
  				if( mimeType.contains(type))
  					ret.add(f.getAbsolutePath());
  			} catch (IOException ignore) {}
  		}
  
  		Collections.sort(ret);
  		return ret;
  	}
docs: Lists all files in the directory with an MIME type that contains the string "type"