Apache HttpComponents Client 4.0快速入门/升级-2.POST方法访问网页

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 POST方法得到www.g.cn的源码：

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.commons.httpclient.NameValuePair;
import org.apache.commons.httpclient.methods.PostMethod;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.ParseException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.protocol.HTTP;
import org.apache.http.util.EntityUtils;
public class PostSample {
    public static void main(String[] args) throws ParseException, IOException {
        String url = "http://www.g.cn/";
        System.out.println(url);
        System.out.println("Visit google using Apache commons-httpclient 3.1：");
        List<NameValuePair> data3 = new ArrayList<NameValuePair>();
        data3.add(new NameValuePair("username", "testuser"));
        data3.add(new NameValuePair("password", "testpassword"));
        System.out.println(post3(url, data3));
        System.out.println("Visit google using Apache HttpComponents Client 4.0：");
        List<BasicNameValuePair> data4 = new ArrayList<BasicNameValuePair>();
        data4.add(new BasicNameValuePair("username", "testuser"));
        data4.add(new BasicNameValuePair("password", "testpassword"));
        System.out.println(post4(url, data4));
    }
    /** 使用Apache commons-httpclient 3.1，POST方法访问网页 */
    public static String post3(String url, List<NameValuePair> data) throws IOException {
        org.apache.commons.httpclient.HttpClient httpClient = new org.apache.commons.httpclient.HttpClient();
        PostMethod postMethod = new PostMethod(url);
        postMethod.setRequestBody(data.toArray(new NameValuePair[data.size()]));
        try {
            System.out.println("<< Response: " + httpClient.executeMethod(postMethod));
            return postMethod.getResponseBodyAsString();
        } finally {
            postMethod.releaseConnection();
        }
    }
    /** 使用Apache HttpComponents Client 4.0，POST方法访问网页 */
    private static String post4(String url, List<? extends org.apache.http.NameValuePair> data)
            throws ParseException, IOException {
        org.apache.http.client.HttpClient client = new DefaultHttpClient();
        HttpPost httpost = new HttpPost(url);
        httpost.setEntity(new UrlEncodedFormEntity(data, HTTP.UTF_8));
        try {
            HttpResponse response = client.execute(httpost);
            HttpEntity entity = response.getEntity();
            System.out.println("<< Response: " + response.getStatusLine());
            if (entity != null) {
                return EntityUtils.toString(entity);
            }
            return null;
        } finally {
            client.getConnectionManager().shutdown();
        }
    }
}

当然www.g.cn不必要通过post来访问，一般用于需要提交表单的情形。