Compare the end of two DataInputStream

Question

I have to create an application that retrieves a xml file on the web, and stores it on the SD card in a Blackberry phone. The xml file is updated by a cron job. So I want the application to download the new xml file if data has been added to this xml file.

For now I compare all the data files using this piece of code

public static boolean isSame( DataInputStream input1, DataInputStream input2 ) throws IOException {
    boolean error = false;
      try {
          byte[] buffer1 = new byte[1024];
          byte[] buffer2 = new byte[1024];
          try {
              int numRead1 = 0;
              int numRead2 = 0;
              while (true) {
                  numRead1 = input1.read(buffer1);
                  numRead2 = input2.read(buffer2);
                  if (numRead1 > -1) {
                      if (numRead2 != numRead1) return false;
                      // Otherwise same number of bytes read
                      if (!Arrays.equals(buffer1, buffer2)) return false;
                      // Otherwise same bytes read, so continue ...
                  } else {
                      // Nothing more in stream 1 ...
                      return numRead2 < 0;
                  }
              }
          } finally {
              input1.close();

          }
      } catch (IOException e) {
          error = true; // this error should be thrown, even if there is an error closing stream 2
          throw e;
      } catch (RuntimeException e) {
          error = true; // this error should be thrown, even if there is an error closing stream 2
          throw e;
      } finally {
          try {
              input2.close();
          } catch (IOException e) {
              if (!error) throw e;
          }
      }
}

It works perfectly, but takes a long time to run.

So is it possible to read the end of the file to see if changes were made, and if so, re-download it ?

Answer 1

In case you don't find a way to read the end of the file: maybe it is possible to create another "mini" file that contains the end that you want to read. So for example if you want to read the last X bytes, then create a new file and write the last X bytes in it. it goes without saying that this file containing the last X bytes needs to be created/updated every time that the XML file gets created/updated by the cron job.

On the device, you store both The XML and the "mini" file. but now you activate your method above on streams to the "mini" files that are found on the server and on the device. If you find that they are not equal, you download both the XML file and also the mini file and override them on the device.