Call an exe from Java with passing parameters with writing to stdout and reading from stdin

Question

I have read this question: Java Programming: call an exe from Java and passing parameters

And this answer is good enough https://stackoverflow.com/a/5604756/2674303

But I additionally want to pass parameters to stdin of external process and read from stdout of this process.

How can I do this?

My efforts:

main method:

public class ProcessBuilderTest {
    public static void main(String[] args) throws IOException, InterruptedException {
        ProcessBuilder pb = new ProcessBuilder("C:\\Program Files\\Java\\jdk1.8.0_111\\bin\\java",
                "-cp", //class path key
                "C:\\Users\\redwhite\\IdeaProjects\\HelloMyWorld\\out\\production\\HelloMyWorld" , // path to class file of ExternalProcess class 
                "call_external.ExternalProcess"); // fully qualified name
        Process process = pb.start();
        OutputStream processOutputStream = process.getOutputStream();
        IOUtils.write("1" + System.lineSeparator(), processOutputStream);
        InputStream processInputStream = process.getInputStream();
        System.out.println("--1--");
        System.out.println(process.isAlive()); // outputs true
        String result = IOUtils.toString(processInputStream, "UTF-8"); //<-- hangs here
        System.out.println("--2--");
        process.waitFor();
        System.out.println(result); // expect to see processed[1]
    }
}

ExternalProcess await string from stdin and produce another string to stdout:

package call_external;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
/**
 * Created by redwhite on 27.03.2017.
 */
public class ExternalProcess {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String input = br.readLine();
        System.out.println("processed[" + input + "]");
    }
}

This code hangs.I cannot understand why

Answer 1

I don't know what the IOUtils class is and what the toString() method is doing. However, a way to read from the InputStream is:

InputStreamReader isr;
BufferedReader br;

String input = "";
String line;

try {

  isr = new InputStreamReader( p.getInputStream );
  br = new BufferedReader( isr );

  while( (line = br.readLine()) != null ) {
    input += line + "\n";
  }

} catch( Exception e ) {
  e.printStackTrace();
}

Answer 2

If I well understood your problem, you are looking for a popen-equivalent function in Java. Maybe this discussion can help you :)

Java: popen()-like function?

Answer 3

Instead of adding \n in the end of line, stream should be closed thus after replacing

IOUtils.write("1" + System.lineSeparator(), processOutputStream);

with

IOUtils.write("1", processOutputStream);
processOutputStream.close();

Code became work properly