Java 8 Future、FutureTask、CompletableFuture 异步任务

本文主要是介绍Java 8 Future、FutureTask、CompletableFuture 异步任务，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

Future 执行异步任务

public class AnswerApp {public static void main(String[] args) throws Exception {ExecutorService executorService = Executors.newCachedThreadPool();Future<Integer> future = executorService.submit(() -> {logger("模拟异步耗时任务开始...");try {// 模拟耗时任务Thread.sleep(5000);} catch (InterruptedException e) {e.printStackTrace();}logger("模拟异步耗时任务结束!!!");return 10;});//当前线程继续做其他事情logger("处理其他事情...\n");// 当前主线程阻塞, 直到获取异步操作的结果Integer result = future.get();logger("result: " + result);}
}

程序运行结果

2019-06-28 18:20:22:618 模拟异步耗时任务开始...
2019-06-28 18:20:22:618 处理其他事情...2019-06-28 18:20:27:622 模拟异步耗时任务结束!!!
2019-06-28 18:20:27:622 result: 10

FutureTask 执行异步任务

public class AnswerApp {public static void main(String[] args) throws Exception {FutureTask<Integer> futureTask = new FutureTask<>(() -> {logger("异步耗时任务开始...");// 模拟耗时任务Thread.sleep(5000);return 100;});ExecutorService executorService = Executors.newCachedThreadPool();executorService.execute(futureTask);// 阻塞, 直到获取异步任务结果logger("result: " + futureTask.get());executorService.shutdown();}
}

程序运行结果

2019-06-28 18:14:46:272 异步耗时任务开始...
2019-06-28 18:14:51:274 result: 100

Future 接口可以执行异步任务，但却有其局限性。它很难直接表述多个 Future 结果之间的依赖性。

将多个异步计算的结果合并成一个
等待 Future 集合中的所有任务都完成
Future 任务完成以后触发执行动作

CompletableFuture 执行异步任务

public class AnswerApp {public static void main(String[] args) throws Exception {CompletableFuture completableFuture = CompletableFuture.supplyAsync(() -> {logger("获取数据(耗时任务)开始...");try {Thread.sleep(5000);} catch (InterruptedException e) {e.printStackTrace();}logger("已经拿到数据啦~~~");return 10;}).thenApply((data) -> {logger(MessageFormat.format("对拿到的·数据{0}·进行加工处理...", data));try {Thread.sleep(2000);} catch (InterruptedException e) {e.printStackTrace();}return data * data;}).whenCompleteAsync((r, e) -> logger("最终数据: " + r));logger("主线程正在执行耗时任务\n");Thread.sleep(3000);logger("主线程耗时任务执行完成\n");completableFuture.get();}
}

程序运行结果

2019-06-28 19:18:40:947 获取数据(耗时任务)开始...
2019-06-28 19:18:40:947 主线程正在执行耗时任务2019-06-28 19:18:43:952 主线程耗时任务执行完成2019-06-28 19:18:45:951 已经拿到数据啦~~~
2019-06-28 19:18:45:971 对拿到的·数据10·进行加工处理...
2019-06-28 19:18:47:972 最终数据: 100

结合两个 CompletableFuture

public class AnswerApp {public static void main(String[] args) throws Exception {CompletableFuture completableFuture = CompletableFuture.supplyAsync(() -> {logger("数据提取数据(耗时任务)...");try {Thread.sleep(5000);} catch (InterruptedException e) {e.printStackTrace();}logger("数据已经拿到啦~~~");return 10;}).thenCompose(preRlt -> CompletableFuture.supplyAsync(() -> {logger("我拿到了上一步任务的数据啦~ preRlt: " + preRlt);try {Thread.sleep(5000);} catch (InterruptedException e) {e.printStackTrace();}return 10 + preRlt;}));logger("最终结果数据: " + completableFuture.get());}
}

程序运行结果

2019-06-28 18:31:44:491 数据提取数据(耗时任务)...
2019-06-28 18:31:49:496 数据已经拿到啦~~~
2019-06-28 18:31:49:499 我拿到了上一步任务的数据啦~ preRlt: 10
2019-06-28 18:31:54:501 最终结果数据: 20

并行执行多个异步任务

public class AnswerApp {public static void main(String[] args) throws Exception {long start = System.currentTimeMillis();CompletableFuture<Integer> completableFuture1 = CompletableFuture.supplyAsync(() -> {logger("耗时·任务1·准备开始...");try {// 模拟耗时任务1Thread.sleep(5000);} catch (InterruptedException e) {e.printStackTrace();}logger("我已经拿到耗时·任务1·的数据啦~~~");return 10;});CompletableFuture<Integer> completableFuture2 = CompletableFuture.supplyAsync(() -> {logger("耗时·任务2·准备开始...");try {// 模拟耗时任务2Thread.sleep(3000);} catch (InterruptedException e) {e.printStackTrace();}logger("我已经拿到耗时·任务2·的数据啦~~~");return 20;});CompletableFuture<Void> combinedFuture = CompletableFuture.allOf(completableFuture1, completableFuture2);// 这个方法不会合并结果，可以看到他的返回值是 Void 类型combinedFuture.get();Optional<Integer> sum = Stream.of(completableFuture1, completableFuture2).map(CompletableFuture::join).reduce((x, y) -> x + y);logger("两个任务的结果和: " + String.valueOf(sum.orElse(0)));logger("程序总共耗时 " + (System.currentTimeMillis() - start) / 1000 + " s");}

程序运行结果

2019-06-28 19:04:20:936 耗时·任务2·准备开始...
2019-06-28 19:04:20:936 耗时·任务1·准备开始...
2019-06-28 19:04:23:939 我已经拿到耗时·任务2·的数据啦~~~
2019-06-28 19:04:25:939 我已经拿到耗时·任务1·的数据啦~~~
2019-06-28 19:04:25:943 两个任务的结果和: 30
2019-06-28 19:04:25:943 程序总共耗时 5 s

异常处理

public class AnswerApp {public static void main(String[] args) throws Exception {String name = null;// 第一个参数为 CompletableFuture 返回的结果, 第二个参数为抛出的异常// s: CompletableFuture 返回的结果, t: 抛出的异常CompletableFuture completableFuture1 = CompletableFuture.supplyAsync(() -> {Assert.notNull(name, "name is null");return MessageFormat.format("hello {0}", name);}).handle((s, t) -> s != null ? s : t.getMessage());logger("最终拿到的结果1: " + completableFuture1.get());System.out.println();String userName = "answer";CompletableFuture completableFuture2 = CompletableFuture.supplyAsync(() -> {Assert.notNull(userName, "userName is null");return MessageFormat.format("hello {0}", userName);}).handle((s, t) -> s != null ? s : t.getMessage());logger("最终拿到的结果2: " + completableFuture2.get());}
}

程序运行结果

2019-06-28 19:07:38:136 最终拿到的结果1: java.lang.IllegalArgumentException: name is null2019-06-28 19:07:38:139 最终拿到的结果2: hello answer

日志打印方法

private static final DateTimeFormatter FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss:SSS");private static void logger(String log) {System.out.println(MessageFormat.format("{0} {1}", LocalDateTime.now().format(FORMATTER), log));
}