Reaching Java application through stdin from command line

Question

I've written a utility in Java that filters JSON input, from a file or from stdin, to XML. Though I've made it a stand-alone, runnable JAR, I'm lost as to how to redirect input to it via stdin. For example:

cat sample.json | java -jar ./target/json-to-xml-1.0.0.jar

This command line doesn't work; I wonder if this can even be done.

  private static String readContentFromStdIn() throws IOException
  {
    char ch;
    StringBuilder sb = new StringBuilder();
    PipedInputStream input = new PipedInputStream();

    while( ( ch = ( char ) input.read() ) != -1 )
      sb.append( ch );

    input.close();

    return sb.toString();
  }

Do you have a case when your program does read from stdin successfully? — 9000
– 9000, Commented Dec 19, 2014 at 17:31
That unix command is correct, I guess your problem is in the code. How are you reading from stdin? System.in? (please paste the relevant code) — morgano
– morgano, Commented Dec 19, 2014 at 17:35

yole · Accepted Answer · 2014-12-19 17:59:41Z

1

Your code is creating a PipedInputStream which is not connected to anything and will never get any data. For reading from stdin, you don't need to create a new stream; you should just read from System.in.

answered Dec 19, 2014 at 17:59

yole

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1 Comment

Russ Bateman Over a year ago

Thank you very much! I adopted Scanner sc=new Scanner(System.in) to read from stdin and it now works.

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