Question

Edit: I really just need to know when a Deflater derived class decides to write header and footer data, and how to exploit those facts. I would really like to do the following:

1. Prime the dictionary for a Deflater derived class with some bytes (I think I got this).

2. Send some data to be compressed to the Deflater derived class (I think I got this).

3. Output all of that compressed data (WITH NO HEADER OR FOOTER DATA) to wherever I want (Not sure how to do this, it would also be okay to have both header/footer, or just one, just as long as it was consistent).

4. Reuse object by starting again at 1.

Original Q: I am using the Java DeflaterOutputStream to compress some data. I am also modifying this compressed data by modifying the headers and the footers. I would like to give some input to DeflaterOutputStream, and have it only output the compressed data part, not the header or footer of the gzip format. How might I do this?

So far, I have been trying to do something like this:

internalWriter.write(storage, 0, amountRead);
internalWriter.finish();
internalWriter.getDef().reset();

internalWriter here is an extension of DeflaterOutputStream. This outputs the compressed data with header and footer. However, on subsequent calls with the same object, it outputs compressed data and footer. I basically want only the compressed data, or perhaps the same thing to happen each time. Any ideas? A quick explanation of how compression streams use close,flush,finish, might help me out too, with a focus on when the header and footer are created and outputted.

And every time I use DeflaterOutputStream, I want it to output everything right away. That is why I did the finish right after the right as seen above…

Answer 1

See the deflater (sic) documentation. If nowrap is true, then there is no header or trailer generated — just raw compressed data in the deflate format.