Capture output of process launched by ProcessBuilder

ProcessBuilderRunner.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringJoiner;

public class ProcessBuilderRunner {

  public static void main(String[] args) {
    final ProcessBuilder pb = new ProcessBuilder(args);
    final String output = runCommandForOutput(pb);
    System.out.printf("full stdout from process: %s\n", output);
  }

  private static String runCommandForOutput(ProcessBuilder processBuilder) {
    Process process;
    String result = "";
    try {
      final String separator = System.getProperty("line.separator");
      final StringJoiner cmdJoiner = new StringJoiner(" ");
      processBuilder.command().forEach(part -> cmdJoiner.add(part));

      System.out.printf("About to run: %s\n", cmdJoiner);
            final StringJoiner joiner = new StringJoiner(separator);
      final StringJoiner errorJoiner = new StringJoiner(separator);

      process = processBuilder.start();

      final Thread outputReaderThread = new Thread(() -> {
        final BufferedReader outputReader = new BufferedReader(new InputStreamReader(process.getInputStream()));
        outputReader.lines().iterator().forEachRemaining(line -> {
          System.out.printf("stdout line: %s\n", line);
          joiner.add(line);
        });
      });

      final Thread errorReaderThread = new Thread(() -> {
        final BufferedReader errorReader = new BufferedReader(new InputStreamReader(process.getErrorStream()));
        errorReader.lines().iterator().forEachRemaining(line -> {
          System.err.printf("stderr line: %s\n", line);
          errorJoiner.add(line);
        });
      });

      outputReaderThread.start();
            errorReaderThread.start();

      final int exitValue = process.waitFor();
      outputReaderThread.join();
      errorReaderThread.join();
      System.out.printf("exit value from process: %d\n", exitValue);
      process.destroy();

      result = joiner.toString();

      System.err.printf("stderr from process: %s\n", errorJoiner.toString());
    } catch (IOException | InterruptedException e) {
      System.err.printf(
          "%s caught when trying to run process and capture stdout/stderr: %s\n",
          e.getClass().getSimpleName(),
          e.getMessage()
      );
      e.printStackTrace(System.err);
    }
    return result;
  }
}