java - 无法从计划的执行程序服务设置 boolean 标志

Question

我需要定期运行一段代码。此代码检查条件并设置 boolean 标志。为了定期运行它，我使用 scheduledExecutorService.scheduleAtFixedRate 方法。

调度程序工作正常，但无法设置标志。标志值始终为 false。

请指教。

package healthCheck;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class Test {
    private static ScheduledExecutorService scheduler;

    public static void main(String[] args) 
            throws InterruptedException, ExecutionException {
        scheduler = Executors.newSingleThreadScheduledExecutor();
        Future<?> scheduledFuture = scheduler.scheduleAtFixedRate(
            new SomeFiveSecondelyJob(),  1, 5, TimeUnit.SECONDS);
        System.out.println("Flag at scheduler"+scheduledFuture.get());
    }

    public static void contextDestroyed() {
        scheduler.shutdownNow();
    }

}

可运行代码:

package healthCheck;

import java.net.URL;

import javax.net.ssl.HttpsURLConnection;

public class SomeFiveSecondelyJob implements Runnable {

    @Override
    public void run() {
        URL url;
        try {
            url = new URL("https://www.google.co.in/");
            HttpsURLConnection connection = 
                (HttpsURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setConnectTimeout(5000);

            int code = connection.getResponseCode();

            if (code / 100 == 2) {
                ItSystemFlag.setFlag(true);
                System.out.println("System is up");

            } else {
                ItSystemFlag.setFlag(false);
                System.out.println("System unavailable: " + code);

            }

        } catch (Exception e) {
            ItSystemFlag.setFlag(false);
            e.printStackTrace();
        }
        System.out.println(ItSystemFlag.getFlag());

    }

}

我使用静态 volatile 变量作为标志:

package healthCheck;

public class ItSystemFlag {
    private static volatile Boolean flag = false;

    public static void setFlag(Boolean flag) {
        ItSystemFlag.flag = flag;
        System.out.println("seting the flag to :" + ItSystemFlag.flag);
    }
    public static Boolean getFlag() {
        return ItSystemFlag.flag;
    }
}

第二个客户端类:

package healthCheck;

public class Test2 {

    public static void main(String[] args) throws InterruptedException {
        for(int i=0;i<20;i++) {
            System.out.println("From client "+ItSystemFlag.getFlag());
            Thread.sleep(6000);
        }
    }

}

Answer 1

这是两个不同的java进程。全局变量不在它们之间共享。尝试:

public class Test {
  private static ScheduledExecutorService scheduler;

  public static void main(String[] args) 
          throws InterruptedException, ExecutionException {
      scheduler = Executors.newSingleThreadScheduledExecutor();
      Future<?> scheduledFuture = scheduler.scheduleAtFixedRate(
          new SomeFiveSecondelyJob(),  1, 5, TimeUnit.SECONDS);
      System.out.println("Flag at scheduler"+scheduledFuture.get());

      for(int i=0;i<20;i++) {
          System.out.println("From client "+ItSystemFlag.getFlag());
          Thread.sleep(6000);
      }
  }

  public static void contextDestroyed() {
      scheduler.shutdownNow();
  }


}

首先运行调度程序，然后在同一个 java 进程中检查全局标志。