CompletableFuture 的簡單示例

在下面的示例中，calculateShippingPrice 方法計算運費，這需要一些處理時間。在現實世界的示例中，這將例如聯絡另一個伺服器，該伺服器基於產品的重量和運輸方法返回價格。

通過 CompletableFuture 以非同步方式對其進行建模，我們可以繼續該方法的不同工作（即計算包裝成本）。

public static void main(String[] args) {
    int price = 15; // Let's keep it simple and work with whole number prices here
    int weightInGrams = 900;
    
    calculateShippingPrice(weightInGrams) // Here, we get the future
        .thenAccept(shippingPrice -> { // And then immediately work on it!
            // This fluent style is very useful for keeping it concise
            System.out.println("Your total price is: " + (price + shippingPrice));
        });
    System.out.println("Please stand by. We are calculating your total price.");
}

public static CompletableFuture<Integer> calculateShippingPrice(int weightInGrams) {
    return CompletableFuture.supplyAsync(() -> { 
        // supplyAsync is a factory method that turns a given 
        // Supplier<U> into a CompletableFuture<U>

        // Let's just say each 200 grams is a new dollar on your shipping costs
        int shippingCosts = weightInGrams / 200;
        
        try {
            Thread.sleep(2000L); // Now let's simulate some waiting time...
        } catch(InterruptedException e) { /* We can safely ignore that */ }

        return shippingCosts; // And send the costs back!
    });
}