JConsole shows threads when run via ProcessBuilder from the process being monitored (Oracle jdk1.8.0_202_linux-x64)

JConsole8Test.java

import java.io.File;
import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.util.concurrent.Executors;

public class JConsole8Test {

  public static void main(String[] args) throws IOException {
    Executors.newSingleThreadExecutor(runnable -> new Thread(runnable, "JConsole8Test")).execute(() -> {
      try {
        Thread.sleep(1000);
      }
      catch (InterruptedException e) {
        e.printStackTrace();
      }
    });

    String javaBin = System.getProperty("java.home") + System.getProperty("file.separator") + "bin";

    new ProcessBuilder().directory(new File(javaBin))
            .command("jconsole", getProcessId())
            .start();
  }

  // Adapted from:
  // https://stackoverflow.com/a/7690178/317760
  private static String getProcessId() {
    final String jvmName = ManagementFactory.getRuntimeMXBean().getName();
    final int index = jvmName.indexOf('@');
    if (index < 1) {
      // part before '@' empty (index = 0) / '@' not found (index = -1)
      return "";
    }

    try {
      return Long.toString(Long.parseLong(jvmName.substring(0, index)));
    }
    catch (NumberFormatException e) {
      return "";
    }
  }
}