Apache HttpComponents Client 4.0快速入门/升级-1.GET方法访问网页

转载自邬贼博客，原文地址：http://blog.csdn.net/inkfish/archive/2009/11/02/4757380.aspx

Apache HttpComponents Client 4.0已经发布多时，httpclient项目从commons子项目挪到了HttpComponents子项目下，httpclient3.1和httpcilent4.0无法做到代码向后兼容，升级比较麻烦。我在做项目之余找时间研究了一下，写了一套3.1与4.0对比的代码，不求面面俱到，但求简单易懂。如果代码用到真实项目中，还需要考虑诸如代理、Header、异常处理之类的问题。

Http GET方法得到www.g.cn的源码：

import java.io.IOException;   
import org.apache.commons.httpclient.HttpException;   
import org.apache.commons.httpclient.HttpStatus;   
import org.apache.commons.httpclient.methods.GetMethod;   
import org.apache.http.client.ClientProtocolException;   
import org.apache.http.client.methods.HttpGet;   
import org.apache.http.impl.client.BasicResponseHandler;   
import org.apache.http.impl.client.DefaultHttpClient;   
public class GetSample {   
    /**  
     * @param args  
     * @throws IOException  
     * @throws HttpException  
     */  
    public static void main(String[] args) throws HttpException, IOException {   
        String url = "http://www.g.cn/";   
        System.out.println(url);   
        System.out.println("Visit google using Apache commons-httpclient 3.1：");   
        System.out.println(get3(url));   
        System.out.println("Visit google using Apache HttpComponents Client 4.0：");   
        System.out.println(get4(url));   
    }   
    /** 使用Apache commons-httpclient 3.1，GET方法访问网页 */  
    public static String get3(String url) throws HttpException, IOException {   
        org.apache.commons.httpclient.HttpClient httpClient = new org.apache.commons.httpclient.HttpClient();   
        GetMethod getMethod = new GetMethod(url);   
        try {   
            if (httpClient.executeMethod(getMethod) != HttpStatus.SC_OK) {   
                System.err.println("Method failed: " + getMethod.getStatusLine());   
            }   
            return getMethod.getResponseBodyAsString();   
        } finally {   
            getMethod.releaseConnection();   
        }   
    }   
    /** 使用Apache HttpComponents Client 4.0，GET方法访问网页 */  
    public static String get4(String url) throws ClientProtocolException, IOException {   
        org.apache.http.client.HttpClient client = new DefaultHttpClient();   
        HttpGet httpget = new HttpGet(url);   
        try {   
            return client.execute(httpget, new BasicResponseHandler());   
        } finally {   
            client.getConnectionManager().shutdown();   
        }   
    }   
}  

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