How to write a byte array to OutputStream of process builder (Java)

Question

byte[] bytes = value.getBytes();
Process q = new ProcessBuilder("process","arg1", "arg2").start();
q.getOutputStream().write(bytes);
q.getOutputStream().flush();
System.out.println(q.getInputStream().available());

I'm trying to stream file contents to an executable and capture the output but the output(InputStream) is always empty. I can capture the output if i specify the the file location but not with streamed input.

How might I overcome this?

Answer 1

Try wrapping your streams with BufferedInputStream() and BufferedOutputStream():

http://download.oracle.com/javase/6/docs/api/java/lang/Process.html#getOutputStream%28%29

Implementation note: It is a good idea for the output stream to be buffered.

Implementation note: It is a good idea for the input stream to be buffered.

Even with buffered streams, it is still possible for the buffer to fill if you're dealing with large amounts of data, you can deal with this by starting a separate thread to read from q.getInputStream(), so you can still be reading from the process while writing to the process.

Answer 2

Perhaps the program you execute only starts its work when it detects the end of its input data. This is normally done by waiting for an EOF (end-of-file) symbol. You can send this by closing the output stream to the process:

q.getOutputStream().write(bytes);
q.getOutputStream().close();

Try this together with waiting for the process.