CompletableFuture及 在stream应用

直接上代码

 public static void main(String[] args) {

        List l = Arrays.asList("1", "2", "3", "5", "4");

        Long start1 = System.currentTimeMillis();
        test1(l);
        System.out.println(System.currentTimeMillis() - start1);
        Long start2 = System.currentTimeMillis();
        test2(l);
        System.out.println(System.currentTimeMillis() - start2);
        Long start3 = System.currentTimeMillis();
        test3(l);
        System.out.println(System.currentTimeMillis() - start3);
        Long start4 = System.currentTimeMillis();
        test4(l);
        System.out.println(System.currentTimeMillis() - start4);
    }

   //普通的顺序处理
    public static List<String> test1(List<String> list){
        return list.stream().map(l -> {
            l = l+l;
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return l;
        }).collect(Collectors.toList());
    }

   //并行流方式处理
    public static List<String> test2(List<String> list){
        return list.parallelStream().map(l -> {
            l = l+l;
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return l;
        }).collect(Collectors.toList());
    }

//CompletableFuture异步请求方式处理
    public static List<String> test3(List<String> list){
        List<CompletableFuture<String>> lists = list.stream().map(l -> CompletableFuture.supplyAsync(()->{try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }return l+l;})
        ).collect(Collectors.toList());

        return lists.stream().map(CompletableFuture::join).collect(Collectors.toList());
    }

//CompletableFuture异步请求方式处理with Executor
    public static List<String> test4(List<String> list){

        Executor executor = Executors.newFixedThreadPool(8, new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                Thread t = new Thread(r);
                t.setDaemon(true);
                return t;
            }
        });

        List<CompletableFuture<String>> lists = list.stream().map(l -> CompletableFuture.supplyAsync(()->{try {
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }return l+l;},executor)
        ).collect(Collectors.toList());

        return lists.stream().map(CompletableFuture::join).collect(Collectors.toList());
    }

执行结果如下：

10088
4011
4003
2003

CompletableFuture

1 )多步处理返回future

CompletableFuture<Integer> f = CompletableFuture.supplyAsync(() -> 2).thenApply(future -> future +
 2).thenApply(future -> future + 2).thenCompose(f1-> CompletableFuture.supplyAsync(()->f1+2));

2 ）处理后消费

CompletableFuture.supplyAsync(() -> 2).thenAccept(System.out::println);

3 ) 完成后做操作

CompletableFuture.supplyAsync(() -> 2).whenComplete((s, throwable) -> System.out.println(s));

4 ) 异常处理 2种方式

CompletableFuture f = CompletableFuture.supplyAsync(() -> 2/0).thenApply(future -> future + 2).thenApply(future -> future + 2).thenCompose(f1-> CompletableFuture.supplyAsync(()->f1+2));
        CompletableFuture exceptionHandler = f.handle((s, th) -> { return (th != null) ? "message upon cancel" : ""; });
        f.completeExceptionally(new RuntimeException("completed exceptionally"));
        System.out.println(exceptionHandler.get());
        System.out.println(f.get());

exceptionHandler 可以继续向下执行。但是f.get会抛出异常无法向下执行

参考：https://juejin.im/post/5cac710ce51d456e2c2484d5
https://segmentfault.com/a/1190000013452165?utm_source=index-hottest