多线程程序包含两个或多个可以同时运行的部分，每个部分可以同时处理不同的任务，从而最大限度地利用可用资源.
你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.
按照步骤执行来自多个线程的请求 :
通过实例化 PoolingHttpClientConnectionManager来创建客户端连接池管理器类.
PoolingHttpClientConnectionManager connManager = new PoolingHttpClientConnectionManager();
使用setMaxTotal()方法设置线程池的最多连接数
//Set the maximum number of connections in the pool connManager.setMaxTotal(100);
通过设置创建 ClientBuilder 对象连接管理器使用 setConnectionManager()方法，如下所示 :
HttpClientBuilder clientbuilder = HttpClients.custom().setConnectionManager(connManager);
通过将所需的URI传递给其构造函数来实例化HttpGet类一个参数.
HttpGet httpget1 = new HttpGet("URI1");
HttpGet httpget2 = new HttpGet("URI2");
. . . . . . . . . . . .确保创建了一个类，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 . . . . . . . . . .
}
}通过实例化创建线程对象上面创建的Thread类(ClientMultiThreaded).
将一个HttpClient对象，相应的HttpGet对象和一个表示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); . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
使用 start()启动所有线程方法并使用join 方法()连接它们.
thread1.start(); thread2.start(); . . . . . . . . thread1.join(); thread2.join(); . . . . . . . . . . . .
在run方法中，执行请求，检索响应并打印结果.
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.IT屋.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();
}
}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
