How to search all files inside a directory using java?

This can be done using dir.list() method of File class.

File dir = new File("directoryName");
      String[] children = dir.list();
      if (children == null) {
         System.out.println("does not exist or 
         is not a directory");
      }
      else {
         for (int i = 0; i < children.length; i++) {
            String filename = children[i];
            System.out.println(filename);
         }
      }