五、ExecutorService的execute和submit方法区别,以及submit使用的具体Demo
1、接收的参数不一样
2、submit有返回值，而execute没有
Method submit extends base method Executor.execute by creating and returning a Future that can be used to cancel execution and/or wait for completion.
用到返回值的例子，比如说我有很多个做validation的task，我希望所有的task执行完，然后每个task告诉我它的执行结果，是成功还是失败，如果是失败，原因是什么。然后我就可以把所有失败的原因综合起来发给调用者。
个人觉得cancel execution这个用处不大，很少有需要去取消执行的。
而最大的用处应该是第二点。
3、submit方便Exception处理
There is a difference when looking at exception handling. If your tasks throws an exception and if it was submitted with execute this exception will Go to the uncaught exception handler (when you don't have provided one explicitly, the default one will just print the stack trace to System.err). If you submitted the task with submit any thrown exception, checked or not, is then part of the task's return status. For a task that was submitted with submit and that terminates with an exception, the Future.get will rethrow this exception, wrapped in an ExecutionException.
意思就是如果你在你的task里会抛出checked或者unchecked exception，而你又希望外面的调用者能够感知这些exception并做出及时的处理，那么就需要用到submit，通过捕获Future.get抛出的异常。
比如说，我有很多更新各种数据的task，我希望如果其中一个task失败，其它的task就不需要执行了。那我就需要catch Future.get抛出的异常，然后终止其它task的执行，代码如下：
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.*; /**
* Created by caoliu on 2017/8/18.
*/
public class ExecutorServiceTest {
public static void main(String[] args) {
ExecutorService executorService = Executors.newCachedThreadPool();
List<Future<String>> resultList = new ArrayList<>(); // 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());
//下面的判读是模拟一个抛出异常的操作
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);
}
}
下面是控制台输出的结果:
call()方法被自动调用,干活！！！ pool-1-thread-1
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-3
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-5
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-7
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-8
call()方法被自动调用,干活！！！ pool-1-thread-9
java.util.concurrent.ExecutionException: TaskException: Meet error in task.pool-1-thread-1
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:188)
at ExecutorServiceTest.main(ExecutorServiceTest.java:26)
Caused by: TaskException: Meet error in task.pool-1-thread-1
at TaskWithResult.call(ExecutorServiceTest.java:54)
at TaskWithResult.call(ExecutorServiceTest.java:37)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745) Process finished with exit code 0