问题描述
我正试图使对多个API的调用更快.
I'm trying to make the calls to multiple APIs faster.
在下面的代码中， getFilteredEvents 是当前同步的版本.我感觉 map(x-> x.getFilteredEvents(eventResearch))操作将等待每个API的响应(它使用 RestTemplate.exchange()内部)，然后再构建下一个要返回的 List< Event> .一种解决方案可能是在单独的线程上启动 map 调用，但我想尝试使用 CompletableFuture API.
In the code below, getFilteredEvents is the currently synchronous version. I have the feeling that the map(x -> x.getFilteredEvents(eventResearch)) operation will wait on the response of each API (it uses RestTemplate.exchange() internally) before passing onto the next one to build the List<Event> that I want to return. A solution would probably be to launch the map call on separate threads, but I wanted to try out the CompletableFuture API.
因此， getFilteredEventsFaster 是我努力改善响应时间的结果.
Thus, getFilteredEventsFaster is the result of my efforts to improve the response time.
@Service
public class EventsResearchService {
@Autowired
private List<UniformEventsResearchApi> eventsResearchApis;
// this works, but I'm trying to improve it
public EventResearchResponse getFilteredEvents(EventResearch eventResearch) {
List<Event> eventsList = eventsResearchApis
.stream()
.map(x -> x.getFilteredEvents(eventResearch))
.flatMap(List::stream)
.collect(Collectors.toList());
return extractResponse(eventResearch, eventsList);
}
// this doesn't work yet: what is wrong?
public CompletableFuture<List<Event>> getFilteredEventsFaster(EventResearch eventResearch) {
List<CompletableFuture<List<Event>>> futureEventsList = eventsResearchApis
.parallelStream()
.map(x -> CompletableFuture.supplyAsync(() -> x.getFilteredEvents(eventResearch)))
.collect(Collectors.toList());
return CompletableFuture.allOf(futureEventsList.toArray(new CompletableFuture<List<Event>>[0]));
}
}
我的理解是我想将 CompletableFuture< List< Event>> 发送回我的前端，而不是将 List< CompletableFuture< List< Event>>; ，因此是 CompletableFuture.allOf()调用(如果我理解正确，它类似于 flatmap 操作，从而创建了 CompletableFuture 来自多个 CompleteableFuture s).
My understanding is that I would want to send a CompletableFuture<List<Event>> back to my frontend, rather than the List<CompletableFuture<List<Event>>>, hence the CompletableFuture.allOf() call (which, if I understood properly, resembles a flatmap operation, creating a CompletableFuture from multiple CompleteableFutures).
不幸的是，使用 new CompletableFuture< List< Event>> [0] 时，出现了通用数组创建编译错误.
Unfortunately, as it is, I get a Generic array creation compilation error when using new CompletableFuture<List<Event>>[0].
我在做什么错了?
我觉得使用 join 方法确实可以让我收集所有答案，但是那将是对Service线程的阻塞操作，不是吗?(如果我理解正确的话，这样做会破坏尝试将 CompletableFuture 返回到我的前端的目的.)
I have the feeling that using the join method would indeed allow me to collect all the answers, but that would be a blocking operation on the thread of my Service, wouldn't it? (Which would defeat the purpose of trying to return a CompletableFuture to my frontend, if I understand correctly.)
推荐答案
以下代码段显示了使用 listOfFutures.stream().map(CompletableFuture :: join)来收集 allOF .我已经从此页面中获取了此示例，该示例指出它不会等待每一个未来都要完成.
The following snippet shows the use of listOfFutures.stream().map(CompletableFuture::join) to collect the result of allOF. I have taken this example from this page that states that it wont wait for every Future to finish.
class Test {
public static void main(String[] args) throws Exception {
long millisBefore = System.currentTimeMillis();
List<String> strings = Arrays.asList("1","2", "3", "4", "5", "6", "7", "8");
List<CompletableFuture<String>> listOfFutures = strings.stream().map(Test::downloadWebPage).collect(toList());
CompletableFuture<List<String>> futureOfList = CompletableFuture
.allOf(listOfFutures.toArray(new CompletableFuture[0]))
.thenApply(v -> listOfFutures.stream().map(CompletableFuture::join).collect(toList()));
System.out.println(futureOfList.get()); // blocks here
System.out.printf("time taken : %.4fs\n", (System.currentTimeMillis() - millisBefore)/1000d);
}
private static CompletableFuture<String> downloadWebPage(String webPageLink) {
return CompletableFuture.supplyAsync( () ->{
try { TimeUnit.SECONDS.sleep(4); }
catch (Exception io){ throw new RuntimeException(io); }
finally { return "downloaded : "+ webPageLink; }
});
}
}
由于效率似乎是这里的问题，因此我添加了一个虚拟基准测试，以证明它不需要32秒即可执行.
Since efficiency seems to be the issue here, I have included a dummy benchmarck to prove it does not take 32 seconds to execute.
输出:
[downloaded : 1, downloaded : 2, downloaded : 3, downloaded : 4, downloaded : 5, downloaded : 6, downloaded : 7, downloaded : 8]
time taken : 8.0630s
原始问题海报中的编辑
通过此答案，并通过使用这个网站(谈论与 allOf 相关的异常处理)，我想出了这个完整的版本:
EDIT from the original Question-Poster
Thanks to this answer, and through using this website (talks about exception handling related to allOf), I came up with this completed version:
public CompletableFuture<List<Event>> getFilteredEventsFaster(EventResearch eventResearch) {
/* Collecting the list of all the async requests that build a List<Event>. */
List<CompletableFuture<List<Event>>> completableFutures = eventsResearchApis.stream()
.map(api -> getFilteredEventsAsync(api, eventResearch))
.collect(Collectors.toList());
/* Creating a single Future that contains all the Futures we just created ("flatmap"). */
CompletableFuture<Void> allFutures =CompletableFuture.allOf(completableFutures
.toArray(new CompletableFuture[eventsResearchApis.size()]));
/* When all the Futures have completed, we join them to create merged List<Event>. */
CompletableFuture<List<Event>> allCompletableFutures = allFutures
.thenApply(future -> completableFutures.stream()
.map(CompletableFuture::join)
.flatMap(List::stream) // creating a List<Event> from List<List<Event>>
.collect(Collectors.toList())
);
return allCompletableFutures;
}
private CompletableFuture<List<Event>> getFilteredEventsAsync(UniformEventsResearchApi api,
EventResearch eventResearch) {
/* Manage the Exceptions here to ensure the wrapping Future returns the other calls. */
return CompletableFuture.supplyAsync(() -> api.getFilteredEvents(eventResearch))
.exceptionally(ex -> {
LOGGER.error("Extraction of events from API went wrong: ", ex);
return Collections.emptyList(); // gets managed in the wrapping Future
});
}
这篇关于返回包含CompletableFutures列表的CompletableFuture的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！