当HttpClient拥有类似PoolingClientConnectionManage类这样的池连接管理器，它就能够使用多线程来并发执行多个请求。

PoolingClientConnectionManager类将根据其配置分配连接。如果给定路由的所有连接都已租用，则会阻塞对连接的请求，直到有连接释放回到连接池。可以通过将“http.conn-manager.timeout”设置为正值来确保连接管理器在连接请求操作中不会无限期地阻塞。如果连接请求不能在给定的期限内提供服务,会抛出ConnectionPoolTimeoutException异常。

PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
CloseableHttpClient httpClient = HttpClients.custom().setConnectionManager(cm).build();// URIs to perform GETs on
String[] urisToGet = {"http://www.domain1.com/","http://www.domain2.com/","http://www.domain3.com/","http://www.domain4.com/"
};// create a thread for each URI
GetThread[] threads = new GetThread[urisToGet.length];
for (int i = 0; i < threads.length; i++) {HttpGet httpget = new HttpGet(urisToGet[i]);threads[i] = new GetThread(httpClient, httpget);
}// start the threads
for (int j = 0; j < threads.length; j++) {threads[j].start();
}// join the threads
for (int j = 0; j < threads.length; j++) {threads[j].join();
}

HttpClient接口的实例是线程安全的，可以在多个执行线程之间共享，强烈建议每个线程维护自己的专用HttpContext接口实例。

static class GetThread extends Thread {private final CloseableHttpClient httpClient;private final HttpContext context;private final HttpGet httpget;public GetThread(CloseableHttpClient httpClient, HttpGet httpget) {this.httpClient = httpClient;this.context = HttpClientContext.create();this.httpget = httpget;}@Overridepublic void run() {try {CloseableHttpResponse response = httpClient.execute(httpget, context);try {HttpEntity entity = response.getEntity();} finally {response.close();}} catch (ClientProtocolException ex) {// Handle protocol errors} catch (IOException ex) {// Handle I/O errors}}}