Reponse outputstream content length?

Question

I am writing to output stream through various methods. How can I, before I close it, find out content length of the outputstream?

Answer 1

You may consider writing to your own ByteArrayOutputStream and flush it to the response output stream at the very end.

Answer 2

The easiest way is probably to wrap it in another OutputStream implementation which forwards on all the write requests, but keeps an internal counter. Then you just write to that instead. Shouldn't be too hard to implement - and indeed there may be one already.

EDIT: Just guessing at a sensible name (CountingOutputStream) came up with an implementation in Apache Commons IO.

Answer 3

The problem is that you must set the content length in the response header before you start writing any data to the output stream. So your options are:

1. Write the data to a byte[] array using ByteOutputStream and then copy that to the response output stream once you have the size of the data. However, if you're writing large files, this obviously isn't an option.
2. Write the data to a temp file and then copy that to the response output once you get the file size. Depending on what you're doing, this may have a performance penalty that is unacceptable.
3. Depending on how expensive it is to generate the data in the first place, you could generate it once, and throw it away to get the count and then generate it again. Guessing that this is unlikely to be a realistic solution.
4. Resign yourself to the fact that you won't be able to report the content length in the response header.