Java 多嵌套 CompletionStage 相当于 "flatMap"？

Question

所以考虑到我有以下示例:

CompletionStage<String> tokenFuture = getToken();

CompletionStage<CompletionStage<CompletionStage<CompletionStage<Boolean>>>> result = tokenFuture.thenApply(token -> {

    WSRequest request = ws.url(url).setHeader("Authorization", "Bearer " + token);

    CompletionStage<WSResponse> response = request.post(json);

    return response.thenApply(r -> {
        if (r.getStatus() == 201) {
            return CompletableFuture.supplyAsync(() -> CompletableFuture.supplyAsync(() -> true));
        } else {
            return getToken().thenApply(t -> {
                WSRequest req = ws.url(url).setHeader("Authorization", "Bearer " + t);
                return req.post(json).thenApply(b -> b.getStatus() == 201);
            });
        }
    });

});

我的问题是整个 CompletionStage<CompletionStage<CompletionStage<CompletionStage<Boolean>>>>多嵌套 future 类型。是否可以将其减少到 CompletionStage<Boolean>通过使用类似 flatMap 的东西在 Scala 中还是有其他方法可以做到这一点？

Answer 1

是的，您正在寻找 thenCompose(fn)操作:

Returns a new CompletionStage that, when this stage completes normally, is executed with this stage as the argument to the supplied function.

此方法采用一个函数作为参数，该函数采用此完成阶段的结果并返回另一个完成阶段。

因此，您可以拥有以下内容:

CompletionStage<String> tokenFuture = getToken();

CompletionStage<Boolean> result = tokenFuture.thenCompose(token -> {

    WSRequest request = ws.url(url).setHeader("Authorization", "Bearer " + token);

    CompletionStage<WSResponse> response = request.post(json);

    return response.thenCompose(r -> {
        if (r.getStatus() == 201) {
            return CompletableFuture.supplyAsync(() -> true);
        } else {
            return getToken().thenCompose(t -> {
                WSRequest req = ws.url(url).setHeader("Authorization", "Bearer " + t);
                return req.post(json).thenApply(b -> b.getStatus() == 201);
            });
        }
    });

});