HttpClient异步请求和指数退避

Question

我需要对可能失败的请求实现指数回退。但是，它是作为异步请求实现的。如果这是同步完成的，我会更好地了解延迟的位置。大致上，我认为它会像这样工作：

// These would be configurable in application.yml
currentAttempt = 0;
maxAttempts = 3;
timeoutGrowth = 2;
currentDelayTime = 5ms;
repeatNeeded = false;
while(repeatNeeded && currentAttempt < maxAttempts) {
httpStatusCode = makeRequest(someService)
if(httpStatusCode == 503) {
repeatNeeded=true;
currentAttempt++;
currentDelayTime*=timeoutGrowthRate;
sleep(currentDelayTime)
}
}

然而，通过异步调用，函数的调用方有时间做其他事情，直到Future有了东西。我是在下面的getObservations((方法中编码回退，还是在该getObservation((方法的调用方中编码回退？以下是目前的呼叫：

public CompletableFuture getObservations(字符串文本、映射<字符串、对象>bodyParams(抛出URISyntaxException{URI URI=getUri(文本(；HttpRequest请求=getRequest(uri，text，bodyParams(；映射<字符串，字符串>contextMap=可选.Nullable(MDC.getCopyOfContextMap(((或Else(Collections.emptyMap((；

Instant startTime = Instant.now();
return httpClient.sendAsync(request, BodyHandlers.ofString())
.exceptionally(ex -> {
throw new ExternalToolException(externalServiceConfig.getName(), ex);
})
.thenApply(response -> {
long toolRequestDurationMillis = ChronoUnit.MILLIS.between(startTime, Instant.now());
if (HttpStatus.valueOf(response.statusCode()).is2xxSuccessful()) {
ToolResponse toolResponse = processResponse(response, toolRequestDurationMillis);
logToolResponse(toolResponse);
return toolResponse;
}
log.error("{} returned non-200 response code: {}", externalServiceConfig.getName(), response.statusCode());
throw new ExternalToolException(externalServiceConfig.getName(), response.statusCode());
});

}

Answer 1

如果您可以考虑使用具有非常强大的API(包括重试(的响应式java。例如，

request()
.retryWhen(Retry.backoff(3, Duration.ofSeconds(2)));
.maxBackoff(5)
.filter(throwable -> isRetryableError(throwable))

还有更多的选项，比如只为特定的异常重试，或者定义最大回退

webClient.get()
.uri("/api")
.retrieve()
.bodyToMono(String.class)
.retryWhen(Retry.backoff(3, Duration.ofSeconds(1)));

您可以使用CompletableFuture，它是一个非阻塞客户端，通过底层的HTTP客户端库(如Reactor Netty (公开流畅、反应式的API

Mono.fromFuture(httpClient.sendAsync(request, BodyHandlers.ofString()))
.retryWhen(Retry.backoff(3, Duration.ofSeconds(1)));

如果出于某种原因，您仍然希望使用HttpClient，则可以包装CCD_3

PD_7