httpclient4.4简单初始化httpclient的方式：

HttpClient httpClient = HttpClientBuilder.create().build();
        ClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory(httpClient);
        restTemplate = new RestTemplate(requestFactory);
  
使用连接池初始化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);
  
但在测试过程中发现，有时候出现如下的异常，但重试一次就没有问题：
 
  
Caused by: org.apache.http.NoHttpResponseException: 10.0.0.25:8080 failed to respond
    at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:143)
    at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:57)
  
网上查了相关的报错信息，找到官网上的描述
 
   
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.
 
  
根据描述主要就是因为服务端断开连接，但并没有通知客户端，导致下次请求该服务时httpclient继续使用该连接导致报错。
 
  
查看了tomcat7的文档，发现在Connector中keepAliveTimeout可以配置连接空闲多久就关闭该连接，它的值默认是和connectionTimeout一样，而在server.xml中connectionTimeout值默认为20s。
 
  
通过验证，确实是在第一次请求20秒后，再请求就会报出NoHttpResponseException的异常。
 
  
通过查看debug日志，以上代码生成的connection默认是keep alive的，通过如下代码可以将httpclient生成的connection的alive时间可配置。
 
  
ConnectionKeepAliveStrategy connectionKeepAliveStrategy = new ConnectionKeepAliveStrategy() {
            @Override
            public long getKeepAliveDuration(HttpResponse httpResponse, HttpContext httpContext) {
                return 20 * 1000; // tomcat默认keepAliveTimeout为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，但这又带来一个问题，所有的连接只有20秒，无法使用长连接的性能优势，在查看API时发现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，后续研究能否使用该API解决短链接的问题。
 
                    摘要: spring resttemplate使用httpclient4.4 连接池，出现org.apache.http.NoHttpResponseException: 10.0.0.25:8080 failed to respond异常的解决方案。以及httpclient4.4版本的连接池配置httpclient4.4简单初始化httpclient的方式：HttpClient 
				
failed to respond 的原因是因为：Http 的 KeepAlive参数引起。
具体可以参考：https://blog.csdn.net/qq826654664jx/article/details/100864080
解决思路：http连接不允许复用；
解决代码：
package com.phkj.equipment.util;
import com.aliyun.oss.common.utils.HttpUtil;
import org.apache.http.Const...
HttpClient 默认使用长连接+连接池。
Http客户端无法及时响应服务端关闭连接，这次如果继续使用这条连接去请求服务端就会导致 org.apache.http.NoHttpResponseException。
虽然HttpClient采取了很多方式避免这种情况，例如请求前会校验超时时间、会读socket检测连接是否还在，但是边界情况总是无法避免（这一刻判断连接可用后，在请求发出去后，接
                    SELECT trim(REGEXP_SUBSTR(a.s,'[^,]+',1,LEVEL)) AS STR FROM DUAL 
   LEFT JOIN (SELECT '17,20,23' AS s FROM dual) a ON 1=1
   CONNECT BY  LEVEL <= LENGTH(a.s)-LENGTH(REGEXP_REPLACE(a.s,',','')) + 1
            error @achrinza/node-ipc@9.2.2: The engine “node“ is incompatible with this module. Expected version
            j-dict-select-tag 下拉框 change事件无效
            AD Ldap pwdLastSet不能更新到指定日期