httpclient使用了连接池，如果没有设置keep-alive策略，PoolingHttpClientConnectionManager会默认使用永久连接。
最近在调用京东api时，发现一个请求开始是可以获取到数据的，但隔了两分钟后再请求就会出现read timeout异常。对比请求成功和请求失败的日志后发现，请求成功的有以下日志“Connection: keep-alive”，“Connection can be kept alive indefinitely”；但请求失败的却打印“Shutdown connection”，“Connection discarded”。每次失败后再请求都会成功。因此推测中应该是对方服务器端禁止长连接，当连接到达一定时间会就会断开。后来上网找到keep-alive策略的代码，添加策略后，问题解决。
1 ConnectionKeepAliveStrategy keepAliveStrategy = new ConnectionKeepAliveStrategy() { 2 ?3 ????????????@Override 4 ????????????public long getKeepAliveDuration(HttpResponse response, HttpContext context) { 5 ????????????????HeaderElementIterator it = new BasicHeaderElementIterator(response.headerIterator(HTTP.CONN_KEEP_ALIVE)); 6 ????????????????while (it.hasNext()) { 7 ????????????????????HeaderElement he = it.nextElement(); 8 ????????????????????String param = he.getName(); 9 ????????????????????String value = he.getValue();10 ????????????????????if (value != null && param.equalsIgnoreCase("timeout")) {11 ????????????????????????try {12 ????????????????????????????return Long.parseLong(value) * 1000;13 ????????????????????????}14 ????????????????????????catch (NumberFormatException ignore) {15 16 ????????????????????????}17 ????????????????????}18 ????????????????}19 ????????????????HttpHost target = (HttpHost) context.getAttribute(HttpClientContext.HTTP_TARGET_HOST);20 ????????????????if ("bizapi.jd.com ".equalsIgnoreCase(target.getHostName())) {21 ????????????????????return 60 * 1000;22 ????????????????}23 ????????????????else {24 ????????????????????return 300 * 1000;25 ????????????????}26 27 ???CloseableHttpClient httpClient = httpClientBuilder.setConnectionManager(pollingConnectionManager)28 ????????????????.setKeepAliveStrategy(keepAliveStrategy).setDefaultRequestConfig(defaultRequestConfig).build();解决httpclient因为保持永久长连接造成连接吊死的问题
原文地址：http://www.cnblogs.com/BensonHe/p/7612474.html