使用线程池执行多线程完毕后的操作

场景：在使用线程池执行多线程之后，获取每个线程获取的数据或是结果的集合，那么在主线程中想要获取完整的集合，就要等子线程执行完毕后，才能获取；

目的：实现子线程执行完毕，再执行子线程；

两种方法：第一种：

ExecutorService executorService = PingVMThreadPool.getInstance().getExecutorService();

//根据list获取具体虚拟机的ip,
for (int i = 0; i < listFromPage.size(); i++) {
   PingVMDeploy engine = null;
   engine = new PingVMDeploy(listFromPage.get(i).toString());
   //线程池提交线程
   executorService.submit(engine);
}
//关闭线程池
executorService.shutdown();

while(true){
   if(executorService.isTerminated()){判断是否线程关闭
      System.out.println("线程结束");
      break;
   }
   try {
      Thread.sleep(2000);
   } catch (InterruptedException e) {
      e.printStackTrace();
   }
}
//在线程关闭之后去获取完整的list集合，否则获取的不完整
ArrayList listFromVM = PingVMDeploy.printList();

这个listFromVM集合是根据子线程中的run方法返回的，具体见下面：


 @Override
    public void run() {
        //这里循环的应该是ip
        boolean flag = MyPing.isOk(ip);
        if(flag){
            arrayList.add(ip);
            System.out.println(ip+",,,");
        }
    }

    //获取所有的arraylist
    public static ArrayList printList(){
        return arrayList;
    }

这样我们需要获取的list集合就能完整的获取到，但是这是一次性的，也就是说，这个shutdown执行完毕之后，这个线程池就不能再使用了 ，再次使用的时候，就会出现下面的问题：

再次使用就会报错：

java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.FutureTask@4a85a05 rejected from java.util.concurrent.ThreadPoolExecutor@50848921[Terminated, pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 15]
at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2063)
at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:830)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1379)
at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:112)
at com.cloudmap.csmc.kernel.cloud.svm.service.SVMRegistService.saveInitsvmAdd(SVMRegistService.java:286)
at com.cloudmap.csmc.kernel.cloud.svm.controller.SVMRegistController.saveInitsvmAdd(SVMRegistController.java:172)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.nutz.mvc.impl.processor.MethodInvokeProcessor.process(MethodInvokeProcessor.java:22)
at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44)
at com.cloudmap.csmc.kernel.AccessControlProcessor.process(SourceFile:141)
at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44)
at com.cloudmap.csmc.kernel.logging.LoggingProcessor.process(SourceFile:71)
at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44)
at org.nutz.mvc.impl.processor.AdaptorProcessor.process(AdaptorProcessor.java:33)
at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44)
at org.nutz.mvc.impl.processor.ActionFiltersProcessor.process(ActionFiltersProcessor.java:40)
at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44)
at org.nutz.mvc.impl.processor.ModuleProcessor.process(ModuleProcessor.java:85)
at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44)
at org.nutz.mvc.impl.processor.EncodingProcessor.process(EncodingProcessor.java:27)
at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44)
at org.nutz.mvc.impl.processor.UpdateRequestAttributesProcessor.process(UpdateRequestAttributesProcessor.java:15)
at org.nutz.mvc.impl.NutActionChain.doChain(NutActionChain.java:40)
at org.nutz.mvc.impl.ActionInvoker.invoke(ActionInvoker.java:64)
at org.nutz.mvc.ActionHandler.handle(ActionHandler.java:31)
at org.nutz.mvc.NutFilter.doFilter(NutFilter.java:101)
at com.cloudmap.csmc.CMNutFilter.doFilter(SourceFile:70)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:660)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:798)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:808)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)

这是什么原因？

因为在第一次使用了线程池之后，他就被shutdown了，所以再次调用线程的时候，就会报出这个异常，（报出这个异常有俩原因，可以参考这篇文章 https://blog.csdn.net/zinss26914/article/details/38922449）

所以呢，怎么解决？

第一种思路：每次调用，重新new一个线程池

第二种思路：也就是第二种方法，

第二种方法：（不关闭线程池，就是每次子线程执行完毕后都会有一个返回值，这样线程池就不必关闭）

继承callabale：

public class PingVMDeploy2 implements Callable {
    
    private String ip;

    public PingVMDeploy2() {
    }

    public PingVMDeploy2(String ip) {
        this.ip = ip;
    }

    public String getIp() {
        return ip;
    }

    public void setIp(String ip) {
        this.ip = ip;
    }

    @Override
    public Object call() throws Exception {
        //这里循环的应该是ip
        boolean flag = MyPing.isOk(ip);
        if(flag){
            return ip;
        }
        return "1";
    }
}


主线程：
ArrayList listFromVM = new ArrayList();

for (int i = 0; i < listFromPage.size(); i++) {
   PingVMDeploy2 engine = null;
   engine = new PingVMDeploy2(listFromPage.get(i).toString());
   Future submit = executorService.submit(engine);

   try {
      if(!submit.get().equals("1")){
         listFromVM.add(submit.get());
      }
   } catch (Exception e) {
      e.printStackTrace();
   }
}

这样就可以线程池不shutdown的时候获取返回数据；

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原文地址：https://www.cnblogs.com/notchangeworld/p/11365643.html