JAVA 线程池之Callable返回结果

import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit; /**
* Created by Administrator on 2017/9/26.
*/
public class FactorialCalculator implements Callable<Integer> { private Integer number; public FactorialCalculator(Integer number) {
this.number = number;
}
public Integer call() throws Exception {
int result = 1; if (number == 0 || number == 1) {
result = 1;
}else {
for (int i = 2; i < number; i++) {
result *= i;
TimeUnit.MICROSECONDS.sleep(200);
if (i == 5) {
throw new IllegalArgumentException("excepion happend");//计算5以上的阶乘都会抛出异常. 根据需要注释该if语句
}
}
}
System.out.printf("%s: %d\n", Thread.currentThread().getName(), result);
return result;
}
}

ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newCachedThreadPool();
List<Future<Integer>> resultList = new ArrayList<Future<Integer>>();
Random random = new Random();
for (int i = 0; i < 10; i ++) {
int rand = random.nextInt(10); FactorialCalculator factorialCalculator = new FactorialCalculator(rand);
Future<Integer> res = executor.submit(factorialCalculator);//异步提交, non blocking.
resultList.add(res);
}

As soon as we invoke the submit() method of ExecutorService the Callable are handed over to ExecutorService to execute.
Here one thing we have to note, the submit() is not blocking.
So, all of our Callables will be submitted right away to the ExecutorService, and ExecutorService will decide when to execute which callable.
For each Callable we get a Future object to get the result later.

do {
// System.out.printf("number of completed tasks: %d\n", executor.getCompletedTaskCount());
for (int i = 0; i < resultList.size(); i++) {
Future<Integer> result = resultList.get(i);
System.out.printf("Task %d : %s \n", i, result.isDone());
}
try {
TimeUnit.MILLISECONDS.sleep(50); } catch (InterruptedException e) {
e.printStackTrace();
}
} while (executor.getCompletedTaskCount() < resultList.size());

System.out.println("Results as folloers:");
for (int i = 0; i < resultList.size(); i++) {
Future<Integer> result = resultList.get(i);
Integer number = null; try {
number = result.get();// blocking method
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
System.out.printf("task: %d, result %d:\n", i, number);
}

We are invoking the get() method of Future to get the result. Here we have to remember that, the get() is a blocking method.

number = result.get()

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.*;/**
* Created by Administrator on 2017/9/26.
*/
public class Main { public static void main(String[] args) {
ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newCachedThreadPool();
List<Future<Integer>> resultList = new ArrayList<Future<Integer>>();
Random random = new Random();
for (int i = 0; i < 10; i ++) {
int rand = random.nextInt(10); FactorialCalculator factorialCalculator = new FactorialCalculator(rand);
Future<Integer> res = executor.submit(factorialCalculator);//异步提交, non blocking.
resultList.add(res);
} // in loop check out the result is finished
do {
// System.out.printf("number of completed tasks: %d\n", executor.getCompletedTaskCount());
for (int i = 0; i < resultList.size(); i++) {
Future<Integer> result = resultList.get(i);
System.out.printf("Task %d : %s \n", i, result.isDone());
}
try {
TimeUnit.MILLISECONDS.sleep(50); } catch (InterruptedException e) {
e.printStackTrace();
}
} while (executor.getCompletedTaskCount() < resultList.size()); System.out.println("Results as folloers:");
for (int i = 0; i < resultList.size(); i++) {
Future<Integer> result = resultList.get(i);
Integer number = null; try {
number = result.get();// blocking method
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
System.out.printf("task: %d, result %d:\n", i, number);
}
executor.shutdown();
}
}