多线程程序包含两个或多个可以并发运行的部分，每个部分可以同时处理不同的任务，从而最佳地利用可用资源。

可以通过编写多线程HttpClient程序来执行来自多个线程的请求。

如果要连续从线程执行多个客户端请求，则需要创建ClientConnectionPoolManager。它维护一个HttpClientConnections池，并提供来自线程的多个请求。

连接管理器根据路由汇集连接。如果管理器具有特定路由的连接，则它通过从池中租用现有连接而不是创建新连接来在这些路由中提供新请求。

按照步骤执行多个线程的请求 -

第1步 - 创建客户端连接池管理器
通过实例化PoolingHttpClientConnectionManager类来创建客户端连接池管理器。

PoolingHttpClientConnectionManager connManager = new
   PoolingHttpClientConnectionManager();

第2步 - 设置最大连接数
使用setMaxTotal()方法设置池中的最大连接数。

//Set the maximum number of connections in the pool
connManager.setMaxTotal(100);

第3步 - 创建ClientBuilder对象
通过使用setConnectionManager()方法设置连接管理器来创建ClientBuilder对象，如下所示 -

HttpClientBuilder clientbuilder =
HttpClients.custom().setConnectionManager(connManager);

第4步 - 创建HttpGet请求对象

通过将所需的URI作为参数传递给其构造函数来实例化HttpGet类。

HttpGet httpget1 = new HttpGet("URI1");
HttpGet httpget2 = new HttpGet("URI2");
. . . . . . . . . . . .

第5步 - 实现run方法
确保已创建一个类，使其成为一个线程(通过扩展线程类或通过实现Runnable接口)并实现run方法。

public class ClientMultiThreaded extends Thread {
   public void run() {
      //Run method implementation . . . . . . . . . .
   }
}

第6步 - 创建Thread对象

通过实例化上面创建的Thread类(ClientMultiThreaded)来创建线程对象。

将HttpClient对象，相应的HttpGet对象和表示ID的整数传递给这些线程。

ClientMultiThreaded thread1 = new ClientMultiThreaded(httpclient,httpget1, 1);
ClientMultiThreaded thread2 = new ClientMultiThreaded(httpclient,httpget2, 2);
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

第7步 - 启动并加入线程
使用start()方法启动所有线程，并使用join()方法加入。

thread1.start();
thread2.start();
. . . . . . . .
thread1.join();
thread2.join();
. . . . . . . . . . . .

第8步 - 运行方法实现

在run方法中，执行请求，检索响应并打印结果。

示例

以下示例演示了从多个线程同时执行HTTP请求。在此示例中，尝试执行来自各种线程的各种请求，并尝试打印状态以及每个客户端读取的字节数。

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.apache.http.util.EntityUtils;

public class ClientMultiThreaded extends Thread {
   CloseableHttpClient httpClient;
   HttpGet httpget;
   int id;

   public ClientMultiThreaded(CloseableHttpClient httpClient, HttpGet httpget,
   int id) {
      this.httpClient = httpClient;
      this.httpget = httpget;
      this.id = id;
   }
   @Override
   public void run() {
      try{
         //Executing the request
         CloseableHttpResponse httpresponse = httpClient.execute(httpget);

         //Displaying the status of the request.
         System.out.println("status of thread "+id+":"+httpresponse.getStatusLine());

         //Retrieving the HttpEntity and displaying the no.of bytes read
         HttpEntity entity = httpresponse.getEntity();
         if (entity != null) {
            System.out.println("Bytes read by thread thread "+id+":
               "+EntityUtils.toByteArray(entity).length);
         }
      }catch(Exception e){
         System.out.println(e.getMessage());
      }
   }

   public static void main(String[] args) throws Exception {

      //Creating the Client Connection Pool Manager by instantiating the PoolingHttpClientConnectionManager class.
      PoolingHttpClientConnectionManager connManager = new PoolingHttpClientConnectionManager();

      //Set the maximum number of connections in the pool
      connManager.setMaxTotal(100);

      //Create a ClientBuilder Object by setting the connection manager
      HttpClientBuilder clientbuilder = HttpClients.custom().setConnectionManager(connManager);

      //Build the CloseableHttpClient object using the build() method.
      CloseableHttpClient httpclient = clientbuilder.build();

      //Creating the HttpGet requests
      HttpGet httpget1 = new HttpGet("http://www.zyiz.net/");
      HttpGet httpget2 = new HttpGet("http://www.zyiz.net/");
      HttpGet httpget3 = new HttpGet("https://www.qries.com/");
      HttpGet httpget4 = new HttpGet("https://in.yahoo.com/");

      //Creating the Thread objects
      ClientMultiThreaded thread1 = new ClientMultiThreaded(httpclient,httpget1, 1);
      ClientMultiThreaded thread2 = new ClientMultiThreaded(httpclient,httpget2, 2);
      ClientMultiThreaded thread3 = new ClientMultiThreaded(httpclient,httpget3, 3);
      ClientMultiThreaded thread4 = new ClientMultiThreaded(httpclient,httpget4, 4);

      //Starting all the threads
      thread1.start();
      thread2.start();
      thread3.start();
      thread4.start();

      //Joining all the threads
      thread1.join();
      thread2.join();
      thread3.join();
      thread4.join();
   }
}

执行上面示例代码，得到以下结果：

status of thread 1: HTTP/1.1 200 OK
Bytes read by thread thread 1: 36907
status of thread 2: HTTP/1.1 200 OK
Bytes read by thread thread 2: 13725
status of thread 3: HTTP/1.1 200 OK
Bytes read by thread thread 3: 17319
status of thread 4: HTTP/1.1 200 OK
Bytes read by thread thread 4: 127018