HttpClient使用详解

Posted 2020-09-08

Http协议的重要性相信不用我多说了，HttpClient相比传统JDK自带的URLConnection，增加了易用性和灵活性（具体区别，日后我们再讨论），它不仅是客户端发送Http请求变得容易，而且也方便了开发人员测试接口（基于Http协议的），即提高了开发的效率，也方便提高代码的健壮性。因此熟练掌握HttpClient是很重要的必修内容，掌握HttpClient后，相信对于Http协议的了解会更加深入。

一、简介

HttpClient是Apache Jakarta Common下的子项目，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已经应用在很多的项目中，比如Apache Jakarta上很著名的另外两个开源项目Cactus和htmlUnit都使用了HttpClient。

下载地址: http://hc.apache.org/downloads.cgi

二、特性

1. 基于标准、纯净的Java语言。实现了Http1.0和Http1.1

2. 以可扩展的面向对象的结构实现了Http全部的方法（GET, POST, PUT, DELETE, HEAD, OPTIONS, and TRACE）。

3. 支持HTTPS协议。

4. 通过Http代理建立透明的连接。

5. 利用CONNECT方法通过Http代理建立隧道的https连接。

6. Basic, Digest, NTLMv1, NTLMv2, NTLM2 Session, SNPNEGO/Kerberos认证方案。

7. 插件式的自定义认证方案。

8. 便携可靠的套接字工厂使它更容易的使用第三方解决方案。

9. 连接管理器支持多线程应用。支持设置最大连接数，同时支持设置每个主机的最大连接数，发现并关闭过期的连接。

10. 自动处理Set-Cookie中的Cookie。

11. 插件式的自定义Cookie策略。

12. Request的输出流可以避免流中内容直接缓冲到socket服务器。

13. Response的输入流可以有效的从socket服务器直接读取相应内容。

14. 在http1.0和http1.1中利用KeepAlive保持持久连接。

15. 直接获取服务器发送的response code和 headers。

16. 设置连接超时的能力。

17. 实验性的支持http1.1 response caching。

18. 源代码基于Apache License 可免费获取。

三、使用方法

使用HttpClient发送请求、接收响应很简单，一般需要如下几步即可。

1. 创建HttpClient对象。

2. 创建请求方法的实例，并指定请求URL。如果需要发送GET请求，创建HttpGet对象；如果需要发送POST请求，创建HttpPost对象。

3. 如果需要发送请求参数，可调用HttpGet、HttpPost共同的setParams(HetpParams params)方法来添加请求参数；对于HttpPost对象而言，也可调用setEntity(HttpEntity entity)方法来设置请求参数。

4. 调用HttpClient对象的execute(HttpUriRequest request)发送请求，该方法返回一个HttpResponse。

5. 调用HttpResponse的getAllHeaders()、getHeaders(String name)等方法可获取服务器的响应头；调用HttpResponse的getEntity()方法可获取HttpEntity对象，该对象包装了服务器的响应内容。程序可通过该对象获取服务器的响应内容。

6. 释放连接。无论执行方法是否成功，都必须释放连接

四、实例

  1 package com.test;  
  2   
  3 import java.io.File;  
  4 import java.io.FileInputStream;  
  5 import java.io.IOException;  
  6 import java.io.UnsupportedEncodingException;  
  7 import java.security.KeyManagementException;  
  8 import java.security.KeyStore;  
  9 import java.security.KeyStoreException;  
 10 import java.security.NoSuchAlgorithmException;  
 11 import java.security.cert.CertificateException;  
 12 import java.util.ArrayList;  
 13 import java.util.List;  
 14   
 15 import javax.net.ssl.SSLContext;  
 16   
 17 import org.apache.http.HttpEntity;  
 18 import org.apache.http.NameValuePair;  
 19 import org.apache.http.ParseException;  
 20 import org.apache.http.client.ClientProtocolException;  
 21 import org.apache.http.client.entity.UrlEncodedFormEntity;  
 22 import org.apache.http.client.methods.CloseableHttpResponse;  
 23 import org.apache.http.client.methods.HttpGet;  
 24 import org.apache.http.client.methods.HttpPost;  
 25 import org.apache.http.conn.ssl.SSLConnectionSocketFactory;  
 26 import org.apache.http.conn.ssl.SSLContexts;  
 27 import org.apache.http.conn.ssl.TrustSelfSignedStrategy;  
 28 import org.apache.http.entity.ContentType;  
 29 import org.apache.http.entity.mime.MultipartEntityBuilder;  
 30 import org.apache.http.entity.mime.content.FileBody;  
 31 import org.apache.http.entity.mime.content.StringBody;  
 32 import org.apache.http.impl.client.CloseableHttpClient;  
 33 import org.apache.http.impl.client.HttpClients;  
 34 import org.apache.http.message.BasicNameValuePair;  
 35 import org.apache.http.util.EntityUtils;  
 36 import org.junit.Test;  
 37   
 38 public class HttpClientTest {  
 39   
 40     @Test  
 41     public void jUnitTest() {  
 42         get();  
 43     }  
 44   
 45     /** 
 46      * HttpClient连接SSL 
 47      */  
 48     public void ssl() {  
 49         CloseableHttpClient httpclient = null;  
 50         try {  
 51             KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());  
 52             FileInputStream instream = new FileInputStream(new File("d:\\tomcat.keystore"));  
 53             try {  
 54                 // 加载keyStore d:\\tomcat.keystore    
 55                 trustStore.load(instream, "123456".toCharArray());  
 56             } catch (CertificateException e) {  
 57                 e.printStackTrace();  
 58             } finally {  
 59                 try {  
 60                     instream.close();  
 61                 } catch (Exception ignore) {  
 62                 }  
 63             }  
 64             // 相信自己的CA和所有自签名的证书  
 65             SSLContext sslcontext = SSLContexts.custom().loadTrustMaterial(trustStore, new TrustSelfSignedStrategy()).build();  
 66             // 只允许使用TLSv1协议  
 67             SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslcontext, new String[] { "TLSv1" }, null,  
 68                     SSLConnectionSocketFactory.BROWSER_COMPATIBLE_HOSTNAME_VERIFIER);  
 69             httpclient = HttpClients.custom().setSSLSocketFactory(sslsf).build();  
 70             // 创建http请求(get方式)  
 71             HttpGet httpget = new HttpGet("https://localhost:8443/myDemo/Ajax/serivceJ.action");  
 72             System.out.println("executing request" + httpget.getRequestLine());  
 73             CloseableHttpResponse response = httpclient.execute(httpget);  
 74             try {  
 75                 HttpEntity entity = response.getEntity();  
 76                 System.out.println("----------------------------------------");  
 77                 System.out.println(response.getStatusLine());  
 78                 if (entity != null) {  
 79                     System.out.println("Response content length: " + entity.getContentLength());  
 80                     System.out.println(EntityUtils.toString(entity));  
 81                     EntityUtils.consume(entity);  
 82                 }  
 83             } finally {  
 84                 response.close();  
 85             }  
 86         } catch (ParseException e) {  
 87             e.printStackTrace();  
 88         } catch (IOException e) {  
 89             e.printStackTrace();  
 90         } catch (KeyManagementException e) {  
 91             e.printStackTrace();  
 92         } catch (NoSuchAlgorithmException e) {  
 93             e.printStackTrace();  
 94         } catch (KeyStoreException e) {  
 95             e.printStackTrace();  
 96         } finally {  
 97             if (httpclient != null) {  
 98                 try {  
 99                     httpclient.close();  
100                 } catch (IOException e) {  
101                     e.printStackTrace();  
102                 }  
103             }  
104         }  
105     }  
106   
107     /** 
108      * post方式提交表单（模拟用户登录请求） 
109      */  
110     public void postForm() {  
111         // 创建默认的httpClient实例.    
112         CloseableHttpClient httpclient = HttpClients.createDefault();  
113         // 创建httppost    
114         HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");  
115         // 创建参数队列    
116         List<namevaluepair> formparams = new ArrayList<namevaluepair>();  
117         formparams.add(new BasicNameValuePair("username", "admin"));  
118         formparams.add(new BasicNameValuePair("password", "123456"));  
119         UrlEncodedFormEntity uefEntity;  
120         try {  
121             uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");  
122             httppost.setEntity(uefEntity);  
123             System.out.println("executing request " + httppost.getURI());  
124             CloseableHttpResponse response = httpclient.execute(httppost);  
125             try {  
126                 HttpEntity entity = response.getEntity();  
127                 if (entity != null) {  
128                     System.out.println("--------------------------------------");  
129                     System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));  
130                     System.out.println("--------------------------------------");  
131                 }  
132             } finally {  
133                 response.close();  
134             }  
135         } catch (ClientProtocolException e) {  
136             e.printStackTrace();  
137         } catch (UnsupportedEncodingException e1) {  
138             e1.printStackTrace();  
139         } catch (IOException e) {  
140             e.printStackTrace();  
141         } finally {  
142             // 关闭连接,释放资源    
143             try {  
144                 httpclient.close();  
145             } catch (IOException e) {  
146                 e.printStackTrace();  
147             }  
148         }  
149     }  
150   
151     /** 
152      * 发送 post请求访问本地应用并根据传递参数不同返回不同结果 
153      */  
154     public void post() {  
155         // 创建默认的httpClient实例.    
156         CloseableHttpClient httpclient = HttpClients.createDefault();  
157         // 创建httppost    
158         HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");  
159         // 创建参数队列    
160         List<namevaluepair> formparams = new ArrayList<namevaluepair>();  
161         formparams.add(new BasicNameValuePair("type", "house"));  
162         UrlEncodedFormEntity uefEntity;  
163         try {  
164             uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");  
165             httppost.setEntity(uefEntity);  
166             System.out.println("executing request " + httppost.getURI());  
167             CloseableHttpResponse response = httpclient.execute(httppost);  
168             try {  
169                 HttpEntity entity = response.getEntity();  
170                 if (entity != null) {  
171                     System.out.println("--------------------------------------");  
172                     System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));  
173                     System.out.println("--------------------------------------");  
174                 }  
175             } finally {  
176                 response.close();  
177             }  
178         } catch (ClientProtocolException e) {  
179             e.printStackTrace();  
180         } catch (UnsupportedEncodingException e1) {  
181             e1.printStackTrace();  
182         } catch (IOException e) {  
183             e.printStackTrace();  
184         } finally {  
185             // 关闭连接,释放资源    
186             try {  
187                 httpclient.close();  
188             } catch (IOException e) {  
189                 e.printStackTrace();  
190             }  
191         }  
192     }  
193   
194     /** 
195      * 发送 get请求 
196      */  
197     public void get() {  
198         CloseableHttpClient httpclient = HttpClients.createDefault();  
199         try {  
200             // 创建httpget.    
201             HttpGet httpget = new HttpGet("http://www.baidu.com/");  
202             System.out.println("executing request " + httpget.getURI());  
203             // 执行get请求.    
204             CloseableHttpResponse response = httpclient.execute(httpget);  
205             try {  
206                 // 获取响应实体    
207                 HttpEntity entity = response.getEntity();  
208                 System.out.println("--------------------------------------");  
209                 // 打印响应状态    
210                 System.out.println(response.getStatusLine());  
211                 if (entity != null) {  
212                     // 打印响应内容长度    
213                     System.out.println("Response content length: " + entity.getContentLength());  
214                     // 打印响应内容    
215                     System.out.println("Response content: " + EntityUtils.toString(entity));  
216                 }  
217                 System.out.println("------------------------------------");  
218             } finally {  
219                 response.close();  
220             }  
221         } catch (ClientProtocolException e) {  
222             e.printStackTrace();  
223         } catch (ParseException e) {  
224             e.printStackTrace();  
225         } catch (IOException e) {  
226             e.printStackTrace();  
227         } finally {  
228             // 关闭连接,释放资源    
229             try {  
230                 httpclient.close();  
231             } catch (IOException e) {  
232                 e.printStackTrace();  
233             }  
234         }  
235     }  
236   
237     /** 
238      * 上传文件 
239      */  
240     public void upload() {  
241         CloseableHttpClient httpclient = HttpClients.createDefault();  
242         try {  
243             HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceFile.action");  
244   
245             FileBody bin = new FileBody(new File("F:\\image\\sendpix0.jpg"));  
246             StringBody comment = new StringBody("A binary file of some kind", ContentType.TEXT_PLAIN);  
247   
248             HttpEntity reqEntity = MultipartEntityBuilder.create().addPart("bin", bin).addPart("comment", comment).build();  
249   
250             httppost.setEntity(reqEntity);  
251   
252             System.out.println("executing request " + httppost.getRequestLine());  
253             CloseableHttpResponse response = httpclient.execute(httppost);  
254             try {  
255                 System.out.println("----------------------------------------");  
256                 System.out.println(response.getStatusLine());  
257                 HttpEntity resEntity = response.getEntity();  
258                 if (resEntity != null) {  
259                     System.out.println("Response content length: " + resEntity.getContentLength());  
260                 }  
261                 EntityUtils.consume(resEntity);  
262             } finally {  
263                 response.close();  
264             }  
265         } catch (ClientProtocolException e) {  
266             e.printStackTrace();  
267         } catch (IOException e) {  
268             e.printStackTrace();  
269         } finally {  
270             try {  
271                 httpclient.close();  
272             } catch (IOException e) {  
273                 e.printStackTrace();  
274             }  
275         }  
276     }  
277 }

 

本实例是采用HttpClient4.3最新版本。该版本与之前的代码写法风格相差较大，大家多留意下。