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。
