Apache HttpClient - 多线程

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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，从而充分利用可用资源。

您可以通过编写多线程 HttpClient 程序来执行来自多个线程的请求。

如果要连续执行来自线程的多个客户端请求，则需要创建一个ClientConnectionPoolManager。它维护一个HttpClientConnections池并为来自线程的多个请求提供服务。

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，那么它会通过从池中租用现有连接来服务这些路由中的新请求，而不是创建新连接。

按照以下步骤执行来自多个线程的请求 -

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

确保您已创建一个类，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 对象以及表示 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 method()连接它们。

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

第 8 步 - Run 方法实现

在 run 方法中，执行请求、检索响应并打印结果。

例子

以下示例演示了从多个线程同时执行 HTTP 请求。在此示例中，我们尝试执行来自各个线程的各种请求，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("https://www.tutorialspoint.com/");
      HttpGet httpget2 = new HttpGet("http://www.google.com/");
      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();
   }
}

输出

执行时，上述程序生成以下输出 -

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