Question

I need to record a stream of data as it passes from my application to another application (both under my control).

I want to do this to record the bytes sent and received for integration testing.

I can do something like this:

void inputStreamToOutputStream(final InputStream inputStream, final OutputStream out) {
    Thread t = new Thread(new Runnable() {

        public void run() {
            try {
                int d;
                while ((d = inputStream.read()) != -1) {
                    out.write(d);
                    savedFile.write(d);
                }
            } catch (IOException ex) {
            }
        }
    });
    t.start();
}

But it feels like there should already be a library to do this. I can see that Apache IOUtils has a copy method to tie two streams together:

IOUtils.copy(in, out);

But this doesn’t let me ‘record’ the bytes sent. Before I go rolling my own, can anyone suggest a decent library that already does this?

Answer 1

With a TeeOutputStream/TeeInputStream from Apache Commons IO, you could write to your output as well as to your savedInFile and savedOutFile:

OutputStream teeOutput = new TeeOutputStream(out, savedOutFile);
InputStream teeInput = new TeeInputStream(input, savedInFile)

and then you can send the tees to your application that does the reading/writing.