Implementing pipes in Java

Question

Need advise on how to implement pipes in Java. Eg,

echo "test"|wc

I need to show results of the above pipe example.

I have tried this:

public class myRunner {

  private static final String[] cmd = new String[] {"wc"};
  public static void main(String[] args){       
    try {
        ProcessBuilder pb = new ProcessBuilder( cmd );
        pb.redirectErrorStream(true);           
        Process process = pb.start();
        OutputStream os = process.getOutputStream();
        os.write("echo test".getBytes() );
        os.close();
    }catch (IOException e){
        e.printStackTrace();
    }

How can I view the output of wc output?

I believe another one of the library i can use is PipedInputStream/PipedOutputStream. Can anyone show an example on how to use it? Am quite confused. thanks

Can you post what you've tried, what you expect it to do and what it does? — Elliott Frisch, Aug 06 '14 at 02:54
Check this post to get clarity of PipedInputSteam[http://stackoverflow.com/questions/3395714/use-cases-of-pipedinputstream-and-pipedoutputstream?lq=1] — randominstanceOfLivingThing, Aug 06 '14 at 03:42
`PipedInput/OutputStreams` are irrelevant to this problem. They are for communicating between threads, not between processes, and when between threads you are almost invariably better off using a Queue of some kind, as stated in my answer to @SureshKoya's cited thread. — user207421, Aug 06 '14 at 04:20

score 1 · Answer 1 · answered Aug 06 '14 at 04:23

1

How can I view the output of wc output?

By consuming the Process's output, via Process.getInputStream(), and reading from it.

answered Aug 06 '14 at 04:23

user207421

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score 0 · Answer 2 · answered May 22 '17 at 10:43

public ArrayList<String> executorPiped(String[] cmd, String outputOld){
    String s=null;
    ArrayList<String> out=new ArrayList<String>();

    try {
        ProcessBuilder pb = new ProcessBuilder( cmd );
        pb.redirectErrorStream(true);
        Process p = pb.start();
        OutputStream os = p.getOutputStream();
        os.write(outputOld.getBytes());
        os.close();

        BufferedReader stdInput = new BufferedReader(new
                InputStreamReader(p.getInputStream()));

        BufferedReader stdError = new BufferedReader(new
                InputStreamReader(p.getErrorStream()));

        while ((s = stdInput.readLine()) != null) {
            out.add(s);
        }
    }catch (IOException io){

    }
    return out;
}

Implementing pipes in Java

2 Answers2