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();
 }

• 9000: Do you have a case when your program does read from stdin successfully?
• morgano: 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)

Answer 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.

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