一、代码
线程池的处理结果、以及处理过程中的异常都被包装到Future中，并在调用Future.get()方法时获取，执行过程中的异常会被包装成ExecutionException，submit()方法本身不会传递结果和任务执行过程中的异常。
我们知道Runable和Callable的区别如下：
1.Runnable执行方法是run(),Callable是call()
2.实现Runnable接口的任务线程无返回值；实现Callable接口的任务线程能返回执行结果
3.call方法可以抛出异常，run方法若有异常只能在内部消化
所以，我们需要获取处理结果和捕获异常需要使用Callable。
/**
* @program: xxx
* @description:
* @author: shuonar
* @create: 2020-06-02 16:52
**/
public class ExecutorsTest {
public static void main(String[] args) {
ExecutorService executorService = new ThreadPoolExecutor(
10,
10,
10, TimeUnit.SECONDS,
new ArrayBlockingQueue<>(512),
new ThreadPoolExecutor.DiscardPolicy());
Callable<String> callable = new Callable<String>() {
@Override
public String call() throws Exception {
throw new RuntimeException("i love exception");
}
};
Future<String> future = executorService.submit(callable);
try{
String result = future.get();
}catch (Exception e){
e.printStackTrace();
}
executorService.shutdown();
}
}
执行结果：
java.util.concurrent.ExecutionException: java.lang.RuntimeException: i love exception
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at com.keda.activiti.config.ExecutorsTest.main(ExecutorsTest.java:29)
Caused by: java.lang.RuntimeException: i love exception
at com.keda.activiti.config.ExecutorsTest$1.call(ExecutorsTest.java:23)
at com.keda.activiti.config.ExecutorsTest$1.call(ExecutorsTest.java:20)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
二、获取单个结果
通过submit()向线程池提交任务后会返回一个Future，调用V Future.get()方法能够阻塞等待执行结果，V get(long timeout, TimeUnit unit)方法可以指定等待的超时时间。
三、获取多个结果
如果向线程池提交了多个任务，要获取这些任务的执行结果，可以依次调用Future.get()获得。
但对于这种场景，我们更应该使用ExecutorCompletionService，该类的take()方法总是阻塞等待某一个任务完成，然后返回该任务的Future对象。向CompletionService批量提交任务后，只需调用相同次数的CompletionService.take()方法，就能获取所有任务的执行结果，获取顺序是任意的，取决于任务的完成顺序：
public class ExecutorTest {
public static void main(String[] args) {
ExecutorService executorService = new ThreadPoolExecutor(
10,
10,
100, TimeUnit.SECONDS,
new ArrayBlockingQueue<>(512),
new ThreadPoolExecutor.AbortPolicy());
List<Callable<String>> solves = new LinkedList<>();
solves.add(new Callable<String>() {
@Override
public String call() throws Exception {
return "i love callable 1";
}
});
solves.add(new Callable<String>() {
@Override
public String call() throws Exception {
Thread.sleep(6000);
return "i love callable 2";
}
});
solves.add(new Callable<String>() {
@Override
public String call() throws Exception {
return "i love callable 3";
}
});
try {
solve(executorService, solves);
}catch (Exception e){
e.printStackTrace();
}
}
private static void solve(Executor executor, Collection<Callable<String>> solves) throws Exception{
CompletionService<String> ecs = new ExecutorCompletionService<String>(executor);
for(Callable<String> solve : solves){
ecs.submit(solve);
}
int size = solves.size();
System.out.println(size);
for (int i = 0; i < size + 1; i++) {
String result = ecs.take().get();
System.out.println(i + "---------" + result);
}
}
}
处理结果：
3
0---------i love callable 1
1---------i love callable 3
2---------i love callable 2
单个任务的超时时间
V Future.get(long timeout, TimeUnit unit)方法可以指定等待的超时时间，超时未完成会抛出TimeoutException
多个任务的超时时间
等待多个任务完成，并设置最大等待时间，可以通过CountDownLatch完成,下篇将详细了解CountDownLatch。待续～～～
