1. CompletableFuture

 CompletableFuture可以进行回调通知、创建异步任务、多个任务前后依赖可以组合处理、对计算速度选最快。
 CompletableFuture提供了一种类似于观察者模式的通知方式，可以在任务完成后通知监听方。
CompletableFuture实例化用CompletableFuture.runAsync()和CompletableFuture.supplyAsync()。

public class demo04 {public static void main(String[] args) {ExecutorService threadPool = Executors.newFixedThreadPool(3);// 无返回值
//        CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(new MyThread4(), threadPool);
//        try {
//            System.out.println(completableFuture.get());
//        } catch (InterruptedException e) {
//            throw new RuntimeException(e);
//        } catch (ExecutionException e) {
//            throw new RuntimeException(e);
//        }// 有返回值CompletableFuture<String> stringCompletableFuture = CompletableFuture.supplyAsync(() -> {try {TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e) {throw new RuntimeException(e);}return "Hello World";});try {System.out.println(stringCompletableFuture.get());} catch (InterruptedException e) {throw new RuntimeException(e);} catch (ExecutionException e) {throw new RuntimeException(e);}// 有返回值CompletableFuture completableFuture = CompletableFuture.supplyAsync(new MyThread5(), threadPool);try {System.out.println(completableFuture.get());} catch (InterruptedException e) {throw new RuntimeException(e);} catch (ExecutionException e) {throw new RuntimeException(e);}threadPool.shutdown();}
}
class MyThread5 implements Supplier {@Overridepublic Object get() {return "Hello Apple";}
}
class MyThread4 implements Runnable {@Overridepublic void run() {try {TimeUnit.SECONDS.sleep(3);System.out.println("Hello World");} catch (InterruptedException e) {throw new RuntimeException(e);}}
}

2. whenCompleted与exceptionally用法

    public static void main(String[] args) {ExecutorService threadPool = Executors.newFixedThreadPool(3);try {CompletableFuture.supplyAsync(()->{int num = 10/0;try {TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e) {throw new RuntimeException(e);}return num;}, threadPool).whenComplete((v,e)->{if(e == null) {System.out.println("Result is " + v);}}).exceptionally(e->{e.printStackTrace();System.out.println(e.getCause() + e.getMessage());return null;});} catch (Exception e) {throw new RuntimeException(e);} finally {threadPool.shutdown();}System.out.println("Main is completed");}

链式调用

public class demo06 {public static void main(String[] args){Stu stu = new Stu();stu.setId("1818").setName("Jack");System.out.println(stu.toString());CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> {return "Hello World";});// 编译时，必须设置对于异常的处理try {System.out.println(completableFuture.get());} catch (InterruptedException e) {throw new RuntimeException(e);} catch (ExecutionException e) {throw new RuntimeException(e);}// 可以不进行设置对于异常的处理String join = completableFuture.join();}
}@AllArgsConstructor
@NoArgsConstructor
// 允许链式调用
@Accessors(chain = true)
@Setter
@Getter
@ToString
class Stu {private String id;private String name;
}

 CompletableFuture的例子。

public class demo07 {public static List<ShopMall> list = Arrays.asList( new ShopMall("taobao"),new ShopMall("jd"),new ShopMall("pdd"),new ShopMall("dangdang"));public static void main(String[] args){System.out.println(extracted("mysql"));}private static List<String> extracted(String productName) {List<String> stringList = list.stream()// 使用CompletableFuture实现多线程异步.map(shopMall -> CompletableFuture.supplyAsync(() -> String.format(productName + "'s price in %s is %.2f", shopMall.getShop(), shopMall.getPrice(productName)))).collect(Collectors.toList()).stream().map(completableFuture -> completableFuture.join()).collect(Collectors.toList());return stringList;}
}@AllArgsConstructor
class ShopMall {@GetterString shop;public Double getPrice(String name) {try {TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e) {throw new RuntimeException(e);}return ThreadLocalRandom.current().nextDouble()*2 + name.charAt(0);}
}

 CompletableFuture的用法：

public class demo08 {public static void main(String[] args) {CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> {try {TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e) {throw new RuntimeException(e);}return "Hello World";});// 需要抛异常// System.out.println(completableFuture.get());// 无需抛异常// System.out.println(completableFuture.join());// 子线程没执行完, 就返回getNow的参数// System.out.println(completableFuture.getNow("Absent"));// 子线程未执行完, complete返回true, join返回complete的参数System.out.println(completableFuture.complete("Absent") + ":" + completableFuture.join());}
}