Java 多线程Future和FutureTask

时间:2021-11-24 02:40:58

Java 多线程Future和FutureTask

Future表示一个任务的周期,并提供了相应的方法来判断是否已经完成或者取消,以及获取任务的结果和取消任务。

Future接口源码:

public interface Future<V> {
boolean cancel(boolean mayInterruptIfRunning);
boolean isCancelled();
boolean isDone();
V get() throws InterruptedException, ExecutionException;
V get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException;
}

Future的demo

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future; public class Main {
public static void main(String[] args) {
ExecutorService executorService = Executors.newCachedThreadPool();
List<Future<String>> resultList = new ArrayList<Future<String>>(); // 创建10个任务并执行
for (int i = 0; i < 10; i++) {
// 使用ExecutorService执行Callable类型的任务,并将结果保存在future变量中
Future<String> future = executorService.submit(new TaskWithResult(i));
// 将任务执行结果存储到List中
resultList.add(future);
}
executorService.shutdown(); // 遍历任务的结果
for (Future<String> fs : resultList) {
try {
System.out.println(fs.get()); // 打印各个线程(任务)执行的结果
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
executorService.shutdownNow();
e.printStackTrace();
return;
}
}
}
}
class TaskWithResult implements Callable<String> {
private int id; public TaskWithResult(int id) {
this.id = id;
} /**
* 任务的具体过程,一旦任务传给ExecutorService的submit方法,则该方法自动在一个线程上执行。
*
* @return
* @throws Exception
*/
public String call() throws Exception {
System.out.println("call()方法被自动调用,干活!!! " + Thread.currentThread().getName());
if (new Random().nextBoolean())
throw new TaskException("Meet error in task." + Thread.currentThread().getName());
// 一个模拟耗时的操作
for (int i = 999999999; i > 0; i--)
;
return "call()方法被自动调用,任务的结果是:" + id + " " + Thread.currentThread().getName();
}
} class TaskException extends Exception {
public TaskException(String message) {
super(message);
}
}
call()方法被自动调用,干活!!!             pool-1-thread-2
call()方法被自动调用,干活!!! pool-1-thread-6
call()方法被自动调用,干活!!! pool-1-thread-1
call()方法被自动调用,任务的结果是:0 pool-1-thread-1
call()方法被自动调用,任务的结果是:1 pool-1-thread-2
call()方法被自动调用,干活!!! pool-1-thread-4
call()方法被自动调用,干活!!! pool-1-thread-9
call()方法被自动调用,干活!!! pool-1-thread-8
call()方法被自动调用,干活!!! pool-1-thread-10
call()方法被自动调用,干活!!! pool-1-thread-5
call()方法被自动调用,干活!!! pool-1-thread-3
call()方法被自动调用,干活!!! pool-1-thread-7
call()方法被自动调用,任务的结果是:2 pool-1-thread-3
call()方法被自动调用,任务的结果是:3 pool-1-thread-4
java.util.concurrent.ExecutionException: com.company.TaskException: Meet error in task.pool-1-thread-5
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at com.company.Main.main(Main.java:29)
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 com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: com.company.TaskException: Meet error in task.pool-1-thread-5
at com.company.TaskWithResult.call(Main.java:56)
at com.company.TaskWithResult.call(Main.java:40)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

FutureTask是一个具体的实现类,ThreadPoolExecutor的submit方法返回的就是一个Future的实现,这个实现就是FutureTask的一个具体实例,FutureTask帮助实现了具体的任务执行,以及和Future接口中的get方法的关联。

Demo:

import java.util.Date;
import java.text.SimpleDateFormat;
import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask; public class Main {
public static void main(String[] args) {
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
// 初始化一个Callable对象和FutureTask对象
Callable pAccount = new PrivateAccount();
FutureTask futureTask = new FutureTask(pAccount);
// 使用futureTask创建一个线程
Thread pAccountThread = new Thread(futureTask);
System.out.println("futureTask线程现在开始启动,启动时间为:" + df.format(new Date()));
pAccountThread.start();
System.out.println("futureTask线程开始执行其他任务");
// 从其他账户获取总金额
int totalMoney = new Random().nextInt(100000);
System.out.println("现在你在其他账户中的总金额为" + totalMoney);
System.out.println("等待私有账户总金额统计完毕...");
// 测试后台的计算线程是否完成,如果未完成则等待
while (!futureTask.isDone()) {
try {
Thread.sleep(500);
System.out.println("私有账户计算未完成继续等待...");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("futureTask线程计算完毕,此时时间为" + df.format(new Date()));
Integer privateAccountMoney = null;
try {
privateAccountMoney = (Integer) futureTask.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
System.out.println("您现在的总金额为:" + totalMoney +"||"+privateAccountMoney.intValue());
}
} class PrivateAccount implements Callable {
Integer totalMoney; @Override
public Object call() throws Exception {
Thread.sleep(5000);
totalMoney = new Integer(new Random().nextInt(10000));
System.out.println("您当前有" + totalMoney + "在您的私有账户中");
return totalMoney;
}
}
futureTask线程现在开始启动,启动时间为:2016-11-30 16:34:57
futureTask线程开始执行其他任务
现在你在其他账户中的总金额为17113
等待私有账户总金额统计完毕...
私有账户计算未完成继续等待...
私有账户计算未完成继续等待...
私有账户计算未完成继续等待...
私有账户计算未完成继续等待...
私有账户计算未完成继续等待...
私有账户计算未完成继续等待...
私有账户计算未完成继续等待...
私有账户计算未完成继续等待...
私有账户计算未完成继续等待...
您当前有8776在您的私有账户中
私有账户计算未完成继续等待...
futureTask线程计算完毕,此时时间为2016-11-30 16:35:02
您现在的总金额为:17113||8776

Demo2:

import java.util.Date;
import java.text.SimpleDateFormat;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask; public class Main {
public static void main(String[] args) {
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
FutureTask<String> futureTask=new FutureTask<>(new Callable<String>() {
//@Override
public String call() throws Exception {
// TODO Auto-generated method stub
return "回调完成";
}
});
Thread thread = new Thread(futureTask);
System.out.println("启动时间为:" + df.format(new Date()));
thread.start();
try {
String str=futureTask.get(); if(str.equals("回调完成"))
System.out.println("异步任务完成!");
else
System.out.println("Completed!");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
启动时间为:2016-12-01 09:37:03
异步任务完成!

http://ifeve.com/futuretask-source/

http://www.liuinsect.com/2014/02/17/futuretask-%E6%BA%90%E7%A0%81%E8%A7%A3%E6%9E%90/

http://blog.csdn.net/ghsau/article/details/7451464

http://blog.csdn.net/javazejian/article/details/50896505