4.5版本的HttpClient中的连接池管理器PoolingHttpClientConnectionManager类实现了HTTP连接池管理，其管理连接的单位为路由(Route)，每个路由维护一定数量(默认是2)的连接；当给定路由的所有连接都被租用时，则新的连接将发生阻塞，直到某连接被释放回连接池。PoolingHttpClientConnectionManager维护的连接次数也受总数MaxTotal(默认是20)的限制。 当HttpClient配置了PoolingHttpClientConnectionManager时，其可以同时执行多个HTTP请求，即实现多线程操作。程序3-22提供了一个简单的多线程请求多URL的案例。由程序3-22所知，使用实例化的PoolingHttpClientConnectionManager可以设置最大连接数Connection信息和Socket信息等。另外，本案例是通过继承Thread类，重写Thread类的run()方法实现的多线程，有兴趣的读者可以通过实现Runnable接口的方式实现多线程。截图为程序在控制台输出的结果。
//程序3-22 public class HttpClientThread { public static void main(String[] args) throws FileNotFoundException { //添加连接参数 ConnectionConfig connectionConfig = ConnectionConfig.custom().setMalformedInputAction(CodingErrorAction.IGNORE).setUnmappableInputAction(CodingErrorAction.IGNORE).setCharset(Consts.UTF_8).build(); //添加socket参数 SocketConfig socketConfig = SocketConfig.custom().setTcpNoDelay(true).build(); //配置连接池管理器 PoolingHttpClientConnectionManager pcm = new PoolingHttpClientConnectionManager(); // 设置最大连接数 pcm.setMaxTotal(100); // 设置每个连接的路由数 pcm.setDefaultMaxPerRoute(10); //设置连接信息 pcm.setDefaultConnectionConfig(connectionConfig); //设置socket信息 pcm.setDefaultSocketConfig(socketConfig); //设置全局请求配置,包括Cookie规范,HTTP认证,超时 RequestConfig defaultConfig = RequestConfig.custom().setCookieSpec(CookieSpecs.STANDARD_STRICT).setExpectContinueEnabled(true).setTargetPreferredAuthSchemes(Arrays.asList(AuthSchemes.NTLM, AuthSchemes.DIGEST)).setProxyPreferredAuthSchemes(Arrays.asList(AuthSchemes.BASIC)).setConnectionRequestTimeout(30*1000).setConnectTimeout(30*1000).setSocketTimeout(30*1000).build(); CloseableHttpClient httpClient = HttpClients.custom().setConnectionManager(pcm).setDefaultRequestConfig(defaultConfig).build(); // 请求的URL String[] urlArr = {"https://hbr.org/podcasts","https://hbr.org/magazine","https://hbr.org/most-popular","https://hbr.org/big-ideas","https://hbr.org/reading-lists"}; //创建固定大小的线程池 ExecutorService exec = Executors.newFixedThreadPool(3); for(int i = 0; i< urlArr.length;i++){ String filename = urlArr[i].split("org/")[1]; //HTML需要输出的文件名 //创建HTML文件输出目录 OutputStream out = new FileOutputStream("/Users/steven/Documents/代码/project/spider/src/main/java/com/topicBet/util/" + filename); HttpGet httpget = new HttpGet(urlArr[i]); //启动线程执行请求 exec.execute(new DownHtmlFileThread(httpClient, httpget, out)); } //关闭线程 exec.shutdown(); } } public class DownHtmlFileThread extends Thread { private final CloseableHttpClient httpClient; private final HttpContext context; private final HttpGet httpget; private final OutputStream out; //输入的参数 public DownHtmlFileThread(CloseableHttpClient httpClient,HttpGet httpget, OutputStream out) { this.httpClient = httpClient; this.context = HttpClientContext.create(); this.httpget = httpget; this.out = out; } @Override public void run() { System.out.println(Thread.currentThread().getName() + "线程请求的URL为:" + httpget.getURI()); try { CloseableHttpResponse response = httpClient.execute(httpget, context); //执行请求 try { //HTML文件写入文档 out.write(EntityUtils.toString(response.getEntity(),"utf-8").getBytes()); out.close(); //消耗实体 EntityUtils.consume(response.getEntity()); } finally{ //关闭响应 response.close(); } } catch (ClientProtocolException ex) { // 处理 protocol错误 ex.printStackTrace(); } catch (IOException ex) { // 处理I/O错误 ex.printStackTrace(); } } }