Running external program with redirected stdin and stdout from Java

Question

I\'m trying to running an external program from a Java program and I\'m having trouble. Basically what I\'d like to do would be this:

 Runtime.getRuntime().e         


        

Answer 1

If you must use Process, then something like this should work:

public static void pipeStream(InputStream input, OutputStream output)
   throws IOException
{
   byte buffer[] = new byte[1024];
   int numRead = 0;

   do
   {
      numRead = input.read(buffer);
      output.write(buffer, 0, numRead);
   } while (input.available() > 0);

   output.flush();
}

public static void main(String[] argv)
{
   FileInputStream fileIn = null;
   FileOutputStream fileOut = null;

   OutputStream procIn = null;
   InputStream procOut = null;

   try
   {
      fileIn = new FileInputStream("test.txt");
      fileOut = new FileOutputStream("testOut.txt");

      Process process = Runtime.getRuntime().exec ("/bin/cat");
      procIn = process.getOutputStream();
      procOut = process.getInputStream();

      pipeStream(fileIn, procIn);
      pipeStream(procOut, fileOut);
   }
   catch (IOException ioe)
   {
      System.out.println(ioe);
   }
}

Note:

• Be sure to close the streams
• Change this to use buffered streams, I think the raw Input/OutputStreams implementation may copy a byte at a time.
• The handling of the process will probably change depending on your specific process: cat is the simplest example with piped I/O.