ProcessBuilder pb = new ProcessBuilder("C:\Program Files\Java\jdk1.8.0_111\bin\java", "-cp", "project_folder\target\classes package.ExternalProcess");
    Process p = pb.start();
    OutputStream processOutputStream = p.getOutputStream();
    IOUtils.write("1" + System.lineSeparator(), processOutputStream);
    InputStream processInputStream = p.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--");
    p.waitFor();
    System.out.println(result);

public class ExternalProcess {
    public static void main(String[] args) {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String input = null;
        try {
            input = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        System.out.println("processed[" + input + "]");
    }
}