httpclient4.4 出現NoHttpResponseException的異常解決

httpclient4.4簡單初始化httpclient的方式：

HttpClient httpClient = HttpClientBuilder.create().build();
ClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory(httpClient);
restTemplate = new RestTemplate(requestFactory);

使用連接池初始化httpclient的方式：

PoolingHttpClientConnectionManager connManager = new PoolingHttpClientConnectionManager();
connManager.setMaxTotal(100);
connManager.setDefaultMaxPerRoute(10);
HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
httpClientBuilder.setConnectionManager(connManager);
httpClientBuilder.setRetryHandler(new DefaultHttpRequestRetryHandler());
HttpClient httpClient = HttpClientBuilder.create().build();
ClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory(httpClient);
restTemplate = new RestTemplate(requestFactory);

但在測試過程中發現，有時候出現如下的異常，但重試一次就沒有問題：

Caused by: org.apache.http.NoHttpResponseException: 10.0.0.25:8080 failed to respondat org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:143)at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:57)

網上查了相關的報錯信息，找到官網上的描述

org.apache.commons.httpclient.NoHttpResponseException java.io.IOException +- org.apache.commons.httpclient.NoHttpResponseExceptionIn some circumstances, usually when under heavy load, the web server may be able to receive requests but unable to process them. A lack of sufficient resources like worker threads is a good example. This may cause the server to drop the connection to the client without giving any response. HttpClient throws NoHttpResponseException when it encounters such a condition. In most cases it is safe to retry a method that failed with NoHttpResponseException.

根據描述主要就是因爲服務端斷開連接，但並沒有通知客戶端，導致下次請求該服務時httpclient繼續使用該連接導致報錯。

查看了tomcat7的文檔，發現在Connector中keepAliveTimeout可以配置連接空閒多久就關閉該連接，它的值默認是和connectionTimeout一樣，而在server.xml中connectionTimeout值默認爲20s。

通過驗證，確實是在第一次請求20秒後，再請求就會報出NoHttpResponseException的異常。

通過查看debug日誌，以上代碼生成的connection默認是keep alive的，通過如下代碼可以將httpclient生成的connection的alive時間可配置。

ConnectionKeepAliveStrategy connectionKeepAliveStrategy = new ConnectionKeepAliveStrategy() {
@Override
public long getKeepAliveDuration(HttpResponse httpResponse, HttpContext httpContext) {
return 20 * 1000; // tomcat默認keepAliveTimeout爲20s
}
};

ConnectionKeepAliveStrategy connectionKeepAliveStrategy = new ConnectionKeepAliveStrategy() {
@Override
public long getKeepAliveDuration(HttpResponse httpResponse, HttpContext httpContext) {
return 20 * 1000; // tomcat默認keepAliveTimeout爲20s
}
};
PoolingHttpClientConnectionManager connManager = new PoolingHttpClientConnectionManager(20, TimeUnit.SECONDS);
connManager.setMaxTotal(200);
connManager.setDefaultMaxPerRoute(200);
RequestConfig requestConfig = RequestConfig.custom()
.setConnectTimeout(10 * 1000)
.setSocketTimeout(10 * 1000)
.setConnectionRequestTimeout(10 * 1000)
.build();
HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
httpClientBuilder.setConnectionManager(connManager);
httpClientBuilder.setDefaultRequestConfig(requestConfig);
httpClientBuilder.setRetryHandler(new DefaultHttpRequestRetryHandler());
httpClientBuilder.setKeepAliveStrategy(connectionKeepAliveStrategy);
HttpClient httpClient = httpClientBuilder.build();
ClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory(httpClient);
restTemplate = new RestTemplate(requestFactory);

主要是增加keepalive的策略，但這又帶來一個問題，所有的連接只有20秒，無法使用長連接的性能優勢，在查看API時發現PoolingHttpClientConnectionManager提供有

@Override
public void closeIdleConnections(final long idleTimeout, final TimeUnit tunit) {
if (this.log.isDebugEnabled()) {
this.log.debug('Closing connections idle longer than ' + idleTimeout + ' ' + tunit);
}
this.pool.closeIdle(idleTimeout, tunit);
}

的方法，後續研究能否使用該API解決短鏈接的問題。

最後把包升級爲4.4.1版本