Java 8: Start process. Keep StdOut and StdErr in the original order. Display output real time character by character. Capture output on exit.

ProcessExample.java

package org.example;

import java.io.IOException;
import java.io.InputStream;
import java.util.Scanner;

public class ProcessExample {

    public static void main(String[] args) {
        ProcessBuilder pb = new ProcessBuilder();
        pb.command("my-executable-name", "arg1");
        
        // Fix "ERROR: Input redirection is not supported, exiting the process immediately" on Windows:
        pb.redirectInput(ProcessBuilder.Redirect.INHERIT);
        // Redirect StdErr to StdOut:
        pb.redirectErrorStream(true);

        try {
            Process proc = pb.start();
            String out = captureOut(proc.getInputStream());
            int exitCode = proc.waitFor();

            System.out.println("------------------------------");
            System.out.println(out);
            System.out.println("Exit code:" + exitCode);
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }

    private static String captureOut(final InputStream src) {
        StringBuilder sb = new StringBuilder();

        Scanner scanner = new Scanner(src);
        scanner.useDelimiter("");
        while (scanner.hasNext()) {
            String symbol = scanner.next();
            System.out.print(symbol);
            sb.append(symbol);
        }

        return sb.toString();
    }

}