java 多嵌套 CompletionStage 等同于 "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。是否可以通过在 Scala 中使用 flatMap 之类的方法将其减少到 CompletionStage<Boolean> 或者是否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和 returns 另一个完成阶段的结果。

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);
            });
        }
    });

});

java 多嵌套 CompletionStage 等同于 "flatMap"？

java multi nested CompletionStage equivalent to "flatMap"?

java

future

completable-future