1. 报错解释

org.apache.http.conn.ConnectionPoolTimeoutException: Timeout waiting for connection 这个异常通常表示在尝试从HTTP连接池获取连接时发生了超时。这可能是因为连接池中没有可用的连接，或者所有的连接都在忙，并且在指定的时间内没有被释放。

2. 场景分析

之前的服务运行了很长时间都很稳定，然后昨天突然出现大量这个报错，后来得知是因为一个三方服务出现了问题，在三方服务故障期间通过HttpClient访问接口返回了非200请求，即使用了连接池，也并不会释放连接，导致连接池阻塞卡死了。所以就出现新的请求从连接池中获取httpClient的时候出现了超时。

3. 解决方案

HttpClient 版本

		<dependency>
			<groupId>org.apache.httpcomponents</groupId>
			<artifactId>httpclient</artifactId>
			<version>4.3.4</version>
		</dependency>
		<dependency>
			<groupId>org.apache.httpcomponents</groupId>
			<artifactId>httpcore</artifactId>
			<version>4.3.2</version>
		</dependency>
		<dependency>
			<groupId>org.apache.httpcomponents</groupId>
			<artifactId>httpmime</artifactId>
			<version>4.3.1</version>
		</dependency>

连接池代码

package com.**.weixin.common.https;
 
import org.apache.http.client.HttpClient;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
 
 
public class HttpClientFactory {
 
    private static final Integer MAX_TOTAL = 300;             //连接池最大连接数
    private static final Integer MAX_PER_ROUTE = 50;          //单个路由默认最大连接数
    private static final Integer REQ_TIMEOUT =  5 * 1000;     //请求超时时间ms
    private static final Integer CONN_TIMEOUT = 5 * 1000;     //连接超时时间ms
    private static final Integer SOCK_TIMEOUT = 10 * 1000;    //读取超时时间ms
    private static HttpClientConnectionMonitorThread thread;  //HTTP链接管理器线程
 
    public static HttpClientConnectionMonitorThread getThread() {
		return thread;
	}
	public static void setThread(HttpClientConnectionMonitorThread thread) {
		HttpClientFactory.thread = thread;
	}
 
	public static HttpClient createSimpleHttpClient(){
		SSLConnectionSocketFactory sf = SSLConnectionSocketFactory.getSocketFactory();
		return HttpClientBuilder.create()
		        .setSSLSocketFactory(sf)
		        .build();
    }
    
	public static HttpClient createHttpClient() {
		PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager();
		poolingHttpClientConnectionManager.setMaxTotal(MAX_TOTAL);
		poolingHttpClientConnectionManager.setDefaultMaxPerRoute(MAX_PER_ROUTE);
		RequestConfig requestConfig = RequestConfig.custom()
				.setConnectionRequestTimeout(REQ_TIMEOUT)
				.setConnectTimeout(CONN_TIMEOUT).setSocketTimeout(SOCK_TIMEOUT)
				.build();
		HttpClientFactory.thread=new HttpClientConnectionMonitorThread(poolingHttpClientConnectionManager); //管理 http连接池
		return HttpClients.custom().setConnectionManager(poolingHttpClientConnectionManager).setDefaultRequestConfig(requestConfig).build();
	}
}

以下 线程用来清理 连接池无效的链接

package com.**.weixin.common.https;
 
import java.util.concurrent.TimeUnit;
 
import org.apache.http.conn.HttpClientConnectionManager;
 
/**
 * <p>Description: 使用管理器，管理HTTP连接池 无效链接定期清理功能</p> 
 * @author andy 2017年8月28日
 */
public class HttpClientConnectionMonitorThread extends Thread {
 
	private final HttpClientConnectionManager connManager;
	private volatile boolean shutdown;
 
	public HttpClientConnectionMonitorThread(HttpClientConnectionManager connManager) {
		super();
		this.setName("http-connection-monitor");
		this.setDaemon(true);
		this.connManager = connManager;
		this.start();
	}
 
	@Override
	public void run() {
		try {
			while (!shutdown) {
				synchronized (this) {
					wait(5000); // 等待5秒
					// 关闭过期的链接
					connManager.closeExpiredConnections();
					// 选择关闭 空闲30秒的链接
					connManager.closeIdleConnections(30, TimeUnit.SECONDS);
				}
			}
		} catch (InterruptedException ex) {
		}
	}
	
	/**
	 * 方法描述: 停止 管理器 清理无效链接  (该方法当前暂时关闭) 
	 * @author andy 2017年8月28日 下午1:45:18
	 */
	@Deprecated
	public void shutDownMonitor() {
		synchronized (this) {
			shutdown = true;
			notifyAll();
		}
	}
 
}

参考文章：https://blog.csdn.net/duxing_langzi/article/details/77772673