Apache HttpClient读取超时后连接关闭延迟问题咨询

我使用Java 11和Spring Boot开发应用，通过RestTemplate调用两个外部REST API，Apache HttpClient配置如下：

@Bean
public RestTemplate proxyRestTemplate() {
  HttpHost proxy = new HttpHost(HTTP_PROXY_HOST, HTTP_PROXY_PORT);
  RequestConfig requestConfig =
      RequestConfig.custom()
          .setProxy(proxy)
          .setCircularRedirectsAllowed(false)
          .setRedirectsEnabled(false)
          .setConnectionRequestTimeout(2000)
          .setConnectTimeout(2000)
          .setSocketTimeout(8000)
          .build();
  PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
  connectionManager.setMaxTotal(40);
  connectionManager.setDefaultMaxPerRoute(20);
  connectionManager.closeExpiredConnections();

  CloseableHttpClient httpClient =
      HttpClientBuilder.create()
          .setConnectionManager(connectionManager)
          .setDefaultRequestConfig(requestConfig)
          .setConnectionManagerShared(true)
          .disableAutomaticRetries()
          .setConnectionTimeToLive(1, TimeUnit.MINUTES)
          .build();

  HttpComponentsClientHttpRequestFactory requestFactory =
      new HttpComponentsClientHttpRequestFactory(httpClient);
  return new RestTemplate(requestFactory);
}

基于该配置，我通过Spring Integration的Http.outboundGateway()调用API，代码如下：

public IntegrationFlow getDecision() {
  return flow -> {
    flow.channel(c -> c.executor(getAsyncExecutor()))
        .handle(
            Http.outboundGateway(myURL, restTemplateConfig.proxyRestTemplate())
                .mappedRequestHeaders("Authorization", "Content-Type")
                .extractPayload(true)
                .httpMethod(HttpMethod.POST)
                .expectedResponseType(String.class));
  };
}

读取超时（已设置为8秒）发生后，连接需要额外7-8秒才能关闭并释放回连接池，导致应用总响应时长增至15-16秒。相关日志记录如下：

DEBUG 2023-09-03T21:00:50.646440127Z [resource.labels.containerName: my-service] http-outgoing-9 >> "{"request":{"Demo request":""}
DEBUG 2023-09-03T21:00:58.651312241Z [resource.labels.containerName: my-service] http-outgoing-9 << "[read] I/O error: Read timed out"
DEBUG 2023-09-03T21:00:58.651390941Z [resource.labels.containerName: my-service] http-outgoing-9: Close connection
DEBUG 2023-09-03T21:01:06.657634687Z [resource.labels.containerName: my-service] http-outgoing-9: Shutdown connection
DEBUG 2023-09-03T21:01:06.657706848Z [resource.labels.containerName: my-service] Connection discarded
DEBUG 2023-09-03T21:01:06.657729276Z [resource.labels.containerName: my-service] Connection released: [id: 9][route: {tls}->http://ep.threatpulse.net:80->https://api.xyz.com:443][total available: 3; route allocated: 3 of 20; total allocated: 4 of 40]

从日志时间线可以看到，读取超时在21:00:58触发，但连接直到21:01:06才完成关闭释放，间隔约8秒。这是因为Apache HttpClient遇到SocketTimeoutException后，默认会尝试优雅关闭连接，如果远端服务器未响应FIN包，就会等待TCP默认超时（通常为2倍MSL，约8秒）后才强制关闭连接。

针对该问题，可通过以下配置优化：

• 强制关闭异常连接，跳过优雅关闭流程
  修改HttpClientBuilder配置，自定义连接复用策略，当请求出现I/O异常时直接标记连接不可复用，立即关闭：

CloseableHttpClient httpClient =
    HttpClientBuilder.create()
        .setConnectionManager(connectionManager)
        .setDefaultRequestConfig(requestConfig)
        .setConnectionManagerShared(true)
        .disableAutomaticRetries()
        .setConnectionTimeToLive(1, TimeUnit.MINUTES)
        // 自定义连接复用策略，异常连接直接关闭
        .setConnectionReuseStrategy(new DefaultConnectionReuseStrategy() {
            @Override
            public boolean keepAlive(HttpResponse response, HttpContext context) {
                IOException ioException = (IOException) context.getAttribute(HttpCoreContext.HTTP_RESPONSE_CONNECTION);
                if (ioException != null) {
                    return false;
                }
                return super.keepAlive(response, context);
            }
        })
        .build();

• 定期主动清理连接池
  当前仅调用closeExpiredConnections()，可添加定时任务定期清理空闲和过期连接，避免连接长时间占用：

// 需在启动类添加@EnableScheduling注解开启定时任务
@Scheduled(fixedRate = 30000)
public void cleanConnectionPool() {
    connectionManager.closeExpiredConnections();
    // 关闭30秒内未使用的空闲连接
    connectionManager.closeIdleConnections(30, TimeUnit.SECONDS);
}

• 双重保障读取超时配置
  在HttpComponentsClientHttpRequestFactory上显式设置读取超时，与RequestConfig的SocketTimeout形成双重保障：

HttpComponentsClientHttpRequestFactory requestFactory =
    new HttpComponentsClientHttpRequestFactory(httpClient);
requestFactory.setReadTimeout(8000); // 与SocketTimeout保持一致

另外，注意setConnectionManagerShared(true)表示连接管理器被多个HttpClient实例共享，需确保所有使用该管理器的客户端都遵循相同的连接策略，避免出现配置冲突。

内容的提问来源于stack exchange，提问作者Somnath Mukherjee