在Java中如何使用CompletableFuture组合多个异步任务_异步任务组合实践技巧

CompletableFuture future = CompletableFuture
    .supplyAsync(() -> "Hello")
    .thenApply(msg -> msg + " World");

future.thenAccept(System.out::println); // 输出: Hello World

CompletableFuture chained = CompletableFuture
    .supplyAsync(() -> "User123")
    .thenCompose(userId -> fetchUserInfoAsync(userId));

// 假设 fetchUserInfoAsync 返回 CompletableFuture

CompletableFuture priceFuture = fetchPriceAsync("item-001");
CompletableFuture taxFuture = calculateTaxAsync(100);

CompletableFuture totalFuture = priceFuture
    .thenCombine(taxFuture, (price, tax) -> price + tax);

totalFuture.thenAccept(total -> System.out.println("总价: " + total));

CompletableFuture task1 = fetchDataAsync("url1");
CompletableFuture task2 = fetchDataAsync("url2");
CompletableFuture task3 = fetchDataAsync("url3");

CompletableFuture allDone = CompletableFuture.allOf(task1, task2, task3);

// 注意：allOf 返回的是 Void，需手动获取各任务结果
allDone.thenRun(() -> {
    try {
        System.out.println("全部完成: " + task1.get() + ", " + task2.get() + ", " + task3.get());
    } catch (Exception e) {
        e.printStackTrace();
    }
});

CompletableFuture safeFuture = fetchDataAsync("broken-url")
    .exceptionally(ex -> {
        System.err.println("加载失败: " + ex.getMessage());
        return "默认内容";
    });

CompletableFuture result = serviceCallAsync()
    .handle((data, ex) -> {
        if (ex != null) {
            log.error("调用失败", ex);
            return "备用数据";
        }
        return data.toUpperCase();
    });

ExecutorService customExecutor = Executors.newFixedThreadPool(4);

CompletableFuture future = CompletableFuture
    .supplyAsync(() -> callRemoteApi(), customExecutor)
    .thenApplyAsync(result -> process(result), customExecutor);

List> futures = urls.stream()
    .map(url -> downloadPageAsync(url))
    .toList();

CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]))
    .join(); // 等待全部完成

List results = futures.stream()
    .map(CompletableFuture::join)
    .toList();