CompletableFuture 中异常处理的 finally 块等价物

Question

我有 CompletableFuture 可以 return 结果或异常。我想在异常和正常结果的情况下执行运行一些通用代码。类似于try catch finally块

当前实施

CompletableFuture<Integer> future= CompletableFuture.supplyAsync(this::findAccountNumber)
                             .thenApply(this::calculateBalance)                      
                             .thenApply(this::notifyBalance)
                             .exceptionally(ex -> {
                                 //My Exception Handling logic 
                                 return 0;
                             });

我可以把我的最终逻辑放在哪里？

Answer 1

handle() 方法提供更灵活的方法。它需要一个函数接收正确的结果或异常：

来自 java 文档

handle(BiFunction<? super T,Throwable,? extends U> fn)

Returns a new CompletionStage that, when this stage completes either normally or exceptionally, is executed with this stage's result and exception as arguments to the supplied function.

CompletableFuture<Integer> thenApply = CompletableFuture.supplyAsync(this::findAccountNumber)
                         .thenApply(this::calculateBalance)                      
                         .thenApply(this::notifyBalance)        
                         .handle((ok, ex) -> {
                            System.out.println("Code That we want to run in finally ");
                            if (ok != null) {
                                    System.out.println("No Exception !!");
                            } else {

                                System.out.println("Got Exception " + ex.getMessage());
                                return -1;
                            }
                            return ok;
                        });

Answer 2

最接近 finally 的是 whenComplete。像 handle 一样，它接受一个接收结果值或 throwable 的函数，但它不提供替换结果值，而是新的完成阶段不会改变结果，就像 finally.

所以

static int decode(String s) {
    try {
        return Integer.parseInt(s);
    }
    finally {
        System.out.println("finally action");
    }
}

相当于

static int decode1(String s) {
    return CompletableFuture.completedFuture(s)
        .thenApply(Integer::parseInt)
        .whenComplete((myParsedInt, error) -> System.out.println("finally action"))
        .join();
}

所以当使用 with

for(String s: Arrays.asList("1234", "foo bar")) try {
    System.out.println("decoded: "+decode(s));
} catch(Exception ex) {
    System.out.println("decoding "+s+" failed with "+ex);
}

第一个变体打印

finally action
decoded: 1234
finally action
decoding foo bar failed with java.lang.NumberFormatException: For input string: "foo bar"

而后者打印

finally action
decoded: 1234
finally action
decoding foo bar failed with java.util.concurrent.CompletionException: java.lang.NumberFormatException: For input string: "foo bar"

两者的共同点是，如果 try 块/前一阶段异常完成，finally 操作中抛出的异常将取代原始结果，隐藏异常。

CompletableFuture 中异常处理的 finally 块等价物

finally block equivalent for exception handling in CompletableFuture

java-8

completable-future