completablefuture join vs get

Question

CompletableFuture.get()和CompletableFuture.join()之间的区别是什么？

以下是我的代码:

List<String> process() {

    List<String> messages = Arrays.asList("Msg1", "Msg2", "Msg3", "Msg4", "Msg5", "Msg6", "Msg7", "Msg8", "Msg9",
            "Msg10", "Msg11", "Msg12");
    MessageService messageService = new MessageService();
    ExecutorService executor = Executors.newFixedThreadPool(4);

    List<String> mapResult = new ArrayList<>();

    CompletableFuture<?>[] fanoutRequestList = new CompletableFuture[messages.size()];
    int count = 0;
    for (String msg : messages) {
        CompletableFuture<?> future = CompletableFuture
                .supplyAsync(() -> messageService.sendNotification(msg), executor).exceptionally(ex -> "Error")
                .thenAccept(mapResult::add);

        fanoutRequestList[count++] = future;
    }

    try {
        CompletableFuture.allOf(fanoutRequestList).get();
      //CompletableFuture.allOf(fanoutRequestList).join();
    } catch (InterruptedException | ExecutionException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    return mapResult.stream().filter(s -> !s.equalsIgnoreCase("Error")).collect(Collectors.toList());
}

我尝试了两种方法,但结果没有差异.

谢谢

Answer 1

唯一的区别是方法如何抛出异常.get()在Future接口中声明为

V get() throws InterruptedException, ExecutionException;

例外是检查的异常,这意味着它们需要在您的代码中处理.正如您在代码中看到的,IDE中的自动代码生成器询问是否代表您创建try-catch块.

try {
  CompletableFuture.allOf(fanoutRequestList).get() 
} catch (InterruptedException | ExecutionException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
}

该join()方法不会抛出已检查的异常.

public T join()

相反,它会抛出未经检查的 CompletionException.因此,您不需要try-catch块,而是exceptionally()在使用disscused List<String> process函数时可以完全利用方法

CompletableFuture<List<String>> cf = CompletableFuture
    .supplyAsync(this::process)
    .exceptionally(this::getFallbackListOfStrings) // Here you can catch e.g. {@code join}'s CompletionException
    .thenAccept(this::processFurther);

你可以在这里找到这两个get()和join()实现

Answer 2

除了 Dawid 提供的答案之外， get 方法还有两种形式：

\n

get()\nget(Long timeout, TimeUnit timeUnit) \n

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第二个get将等待时间作为参数，并最多等待提供的等待时间。

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try {\n    System.out.println(cf.get(1000, TimeUnit.MILLISECONDS));\n} catch (InterruptedException | ExecutionException | TimeoutException ex) {\n    ex.printStackTrace();\n}\n

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您可以参考此文档以获取更多信息。

\n

\n
1. join()\xc2\xa0定义在\xc2\xa0CompletableFuture\xc2\xa0中，而\xc2\xa0get()\xc2\xa0来自接口\xc2\xa0Future
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2. join()\xc2\xa0抛出未检查的异常，而\xc2\xa0get()\xc2\xa0抛出检查的异常
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3. 您可以中断 get()\xc2\xa0 然后抛出 \xc2\xa0InterruptedException
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4. get() 方法允许指定最大等待时间
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