Using Java to run a Python application and then parse its output

Question

So I'm currently working on a project which is using Java for it's GUI and a python script to perform the primary functions of the program.

I was wondering if there is a way to run the python script from within the application directory, and then send its output to the GUI program for parsing. The output could be JSON/YAML/Plaintext etc (so this will be parsed by the GUI).

Two options I thought of (which may or may not work) were:

Running the Python program separately and having it output a file which is then read by the Java program (This is my least favourite)
Using ProcessBuilder or Runtime.exec to run the Python program.. But then how would I get the output?

If neither of my options I thought of are feasible or would work, then is there a way to do this much better?

Thanks!

Both would work, but I'd prefer ProcessBuilder#redirectOutput(Redirect) and redirectError. Use separate threads for reading from the stream, otherwise the process may hang after filling its output buffers. — maaartinus
– maaartinus, Commented Dec 30, 2017 at 23:02

nkprince007 · Accepted Answer · 2017-12-30 09:40:00Z

1

Runtime.exec gives you an input stream that can be wrapped in a buffered reader to parse the output.

      try {

        Process p = Runtime.getRuntime().exec("python 1.py'");

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

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

        // read the output from the command
        System.out.println("Here is the standard output of the command:\n");
        while ((s = stdInput.readLine()) != null) {
            System.out.println(s);
        }

        // read any errors from the attempted command
        System.out.println("Here is the standard error of the command (if any):\n");
        while ((s = stdError.readLine()) != null) {
            System.out.println(s);
        }

        System.exit(0);
    }
    catch (IOException e) {
        System.out.println("exception happened - here's what I know: ");
        e.printStackTrace();
        System.exit(-1);
    }

edited Dec 30, 2017 at 9:40

answered Dec 28, 2017 at 14:09

nkprince007

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1 Comment

rshah Over a year ago

Your example is quite unclear. To me it just looks like your reading in a file called write.txt, so it doesn't really answer my question as to whether I can effectively execute the python script to get its output

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