我正在尝试使对多个API的调用更快。
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(内部使用RestTemplate.exchange()
),然后传递到下一个API,以构建要返回的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CompletableFuture
API。
因此,getFilteredEventsFaster
是我努力改善响应时间的结果。
@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List<CompletableFuture<List<Event>>>
,因此,CompletableFuture.allOf()
调用(如果我理解正确,它类似于flatmap
操作,创建了一个CompletableFuture
来自多个CompleteableFuture
)。
不幸的是,使用Generic array creation
时出现new CompletableFuture<List<Event>>[0]
编译错误。
我在做什么错?
我感觉使用join
方法确实可以收集所有答案,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。)
以下代码段显示了使用listOfFutures.stream().map(CompletableFuture::join)
来收集allOF
的结果。我从this page中选取了此示例,该示例指出它不会等待每个Future完成。
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; }
});
}
}
因为效率似乎是这里的问题,所以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。
输出:
[downloaded : 1, downloaded : 2, downloaded : 3, downloaded : 4, downloaded : 5, downloaded : 6, downloaded : 7, downloaded : 8]
time taken : 8.0630s