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：

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1. import java.io.IOException;
2. import java.util.ArrayList;
3. import java.util.List;
4. import org.apache.commons.httpclient.NameValuePair;
5. import org.apache.commons.httpclient.methods.PostMethod;
6. import org.apache.http.HttpEntity;
7. import org.apache.http.HttpResponse;
8. import org.apache.http.ParseException;
9. import org.apache.http.client.entity.UrlEncodedFormEntity;
10. import org.apache.http.client.methods.HttpPost;
11. import org.apache.http.impl.client.DefaultHttpClient;
12. import org.apache.http.message.BasicNameValuePair;
13. import org.apache.http.protocol.HTTP;
14. import org.apache.http.util.EntityUtils;
15. public class PostSample {
16. public static void main(String[] args) throws ParseException, IOException {
17. String url = "http://www.g.cn/";
18. System.out.println(url);
19. System.out.println("Visit google using Apache commons-httpclient 3.1：");
20. List<NameValuePair> data3 = new ArrayList<NameValuePair>();
21. data3.add(new NameValuePair("username", "testuser"));
22. data3.add(new NameValuePair("password", "testpassword"));
23. System.out.println(post3(url, data3));
24. System.out.println("Visit google using Apache HttpComponents Client 4.0：");
25. List<BasicNameValuePair> data4 = new ArrayList<BasicNameValuePair>();
26. data4.add(new BasicNameValuePair("username", "testuser"));
27. data4.add(new BasicNameValuePair("password", "testpassword"));
28. System.out.println(post4(url, data4));
29. }
30. /** 使用Apache commons-httpclient 3.1，POST方法访问网页 */
31. public static String post3(String url, List<NameValuePair> data) throws IOException {
32. org.apache.commons.httpclient.HttpClient httpClient = new org.apache.commons.httpclient.HttpClient();
33. PostMethod postMethod = new PostMethod(url);
34. postMethod.setRequestBody(data.toArray(new NameValuePair[data.size()]));
35. try {
36. System.out.println("<< Response: " + httpClient.executeMethod(postMethod));
37. return postMethod.getResponseBodyAsString();
38. } finally {
39. postMethod.releaseConnection();
40. }
41. }
42. /** 使用Apache HttpComponents Client 4.0，POST方法访问网页 */
43. private static String post4(String url, List<? extends org.apache.http.NameValuePair> data)
44. throws ParseException, IOException {
45. org.apache.http.client.HttpClient client = new DefaultHttpClient();
46. HttpPost httpost = new HttpPost(url);
47. httpost.setEntity(new UrlEncodedFormEntity(data, HTTP.UTF_8));
48. try {
49. HttpResponse response = client.execute(httpost);
50. HttpEntity entity = response.getEntity();
51. System.out.println("<< Response: " + response.getStatusLine());
52. if (entity != null) {
53. return EntityUtils.toString(entity);
54. }
55. return null;
56. } finally {
57. client.getConnectionManager().shutdown();
58. }
59. }
60. }

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。