File random access in J2ME

Question

does J2ME have something similar to RandomAccessFile class, or is there any way to emulate this particular (random access) functionality?

The problem is this: I have a rather large binary data file (~600 KB) and would like to create a mobile application for using that data. Format of that data is home-made and contains many index blocks and data blocks. Reading the data on other platforms (like PHP or C) usually goes like this:

1. Read 2 bytes for index key (K), another 2 for index value (V) for the data type needed
2. Skip V bytes from the start of the file to seek to a file position there the data for index key K starts
3. Read the data
4. Profit :)

This happens many times during the program flow.

Um, and I'm investigating possibility of doing the very same on J2ME, and while I admit I'm quite new to the whole Java thing, I can't seem to be able to find anything beyond InputStream (DataInputStream) classes which don't have the basic seeking/skipping to byte/returning position functions I need.

So, what are my chances?

Transistorize

Answer 1

You should have something like this

try {
    DataInputStream di = new DataInputStream(is);
    di.marke(9999);
    short key = di.readShort();
    short val = di.readShort();
    di.reset();
    di.skip(val);
    byte[] b= new byte[255];
    di.read(b);
}catch(Exception ex ) {
    ex.printStackTrace();
}

I prefer not to use the marke/reset methods, I think it is better to save the offset from the val location not from the start of the file so you can skip these methods. I think they have som issues on some devices.

One more note, I don't recommend to open a 600 KB file, it will crash the application on many low end devices, you should split this file to multiple files.

Ecology

Hi, thanks for your answer! But then, how to you effectively seek to the position that is lower than the current position? (Say, you just read a byte at position 100, and now you need a byte at position 50)? – Transistorize

unfortunately there is no way other than using marke/reset methods in this case. – Ecology

I want to write at random places by providing offsets in file in j2me.Is there any way? – Bottle