HttpClient

HttpClient 是 Apache Jakarta Common 下的子项目，可以用来提供高效的、最新的、功能丰富的支持 HTTP 协议的客户端编程工具包，并且它支持 HTTP 协议最新的版本和建议。
HttpClient下载地址：http://hc.apache.org/downloads.cgi
示例是api中的一个examples：
package org.apache.http.examples;

import java.net.Socket;

import org.apache.http.ConnectionReuseStrategy;
import org.apache.http.HttpHost;
import org.apache.http.HttpResponse;
import org.apache.http.HttpVersion;
import org.apache.http.impl.DefaultConnectionReuseStrategy;
import org.apache.http.impl.DefaultHttpClientConnection;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.message.BasicHttpRequest;
import org.apache.http.params.HttpParams;
import org.apache.http.params.HttpProtocolParams;
import org.apache.http.protocol.BasicHttpProcessor;
import org.apache.http.protocol.HttpContext;
import org.apache.http.protocol.BasicHttpContext;
import org.apache.http.protocol.ExecutionContext;
import org.apache.http.protocol.HttpRequestExecutor;
import org.apache.http.protocol.RequestConnControl;
import org.apache.http.protocol.RequestContent;
import org.apache.http.protocol.RequestExpectContinue;
import org.apache.http.protocol.RequestTargetHost;
import org.apache.http.protocol.RequestUserAgent;
import org.apache.http.util.EntityUtils;

/**
* Elemental example for executing a GET request.
* <p>
* Please note the purpose of this application is demonstrate the usage of HttpCore APIs.
* It is NOT intended to demonstrate the most efficient way of building an HTTP client.
*
*
*
* <!-- empty lines above to avoid 'svn diff' context problems -->
* @version $Revision: 744516 $
*/
public class ElementalHttpGet {

    public static void main(String[] args) throws Exception {
       
        HttpParams params = new BasicHttpParams();
        HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
        HttpProtocolParams.setContentCharset(params, "UTF-8");
        HttpProtocolParams.setUserAgent(params, "HttpComponents/1.1");
        HttpProtocolParams.setUseExpectContinue(params, true);

        BasicHttpProcessor httpproc = new BasicHttpProcessor();
        // Required protocol interceptors
        httpproc.addInterceptor(new RequestContent());
        httpproc.addInterceptor(new RequestTargetHost());
        // Recommended protocol interceptors
        httpproc.addInterceptor(new RequestConnControl());
        httpproc.addInterceptor(new RequestUserAgent());
        httpproc.addInterceptor(new RequestExpectContinue());

        HttpRequestExecutor httpexecutor = new HttpRequestExecutor();
       
        HttpContext context = new BasicHttpContext(null);
        HttpHost host = new HttpHost("www.google.com", 80);

        DefaultHttpClientConnection conn = new DefaultHttpClientConnection();
        ConnectionReuseStrategy connStrategy = new DefaultConnectionReuseStrategy();

        context.setAttribute(ExecutionContext.HTTP_CONNECTION, conn);
        context.setAttribute(ExecutionContext.HTTP_TARGET_HOST, host);

        try {
           
            String[] targets = {"/"};
           
            for (int i = 0; i < targets.length; i++) {
                if (!conn.isOpen()) {
                    Socket socket = new Socket(host.getHostName(), host.getPort());
                    conn.bind(socket, params);
                }
                BasicHttpRequest request = new BasicHttpRequest("GET", targets[i]);
                System.out.println(">> Request URI: " + request.getRequestLine().getUri());
               
                request.setParams(params);
                httpexecutor.preProcess(request, httpproc, context);
                HttpResponse response = httpexecutor.execute(request, conn, context);
                response.setParams(params);
                httpexecutor.postProcess(response, httpproc, context);
               
                System.out.println("<< Response: " + response.getStatusLine());
                System.out.println(EntityUtils.toString(response.getEntity()));
               System.out.println("==============");
                if (!connStrategy.keepAlive(response, context)) {
                    conn.close();
                } else {
                    System.out.println("Connection kept alive...");
                }
            }
        } finally {
            conn.close();
        }
    }
   
}