How do I handle multiple streams in Java?

Question

I'm trying to run a process and do stuff with its input, output and error streams. The obvious way to do this is to use something like select(), but the only thing I can find in Java that does that is Selector.select(), which takes a Channel. It doesn't appear to be possible to get a Channel from an InputStream or OutputStream (FileStream has a getChannel() method but that doesn't help here)

So, instead I wrote some code to poll all the streams:

while( !out_eof || !err_eof )
{
    while( out_str.available() )
    {
        if( (bytes = out_str.read(buf)) != -1 )
        {
            // Do something with output stream
        }
        else
            out_eof = true;
    }
    while( err_str.available() )
    {
        if( (bytes = err_str.read(buf)) != -1 )
        {
            // Do something with error stream
        }
        else
            err_eof = true;
    }
    sleep(100);
}

which works, except that it never terminates. When one of the streams reaches end of file, available() returns zero so read() isn't called and we never get the -1 return that would indicate EOF.

One solution would be a non-blocking way to detect EOF. I can't see one in the docs anywhere. Alternatively is there a better way of doing what I want to do?

I see this question here: link text and although it doesn't exactly do what I want, I can probably use that idea, of spawning separate threads for each stream, for the particular problem I have now. But surely that isn't the only way to do it? Surely there must be a way to read from multiple streams without using a thread for each?

Answer 1

As you said, the solution outlined in this Answer is the traditional way of reading both stdout and stderr from a Process. A thread-per-stream is the way to go, even though it is slightly annoying.