HttpClient 在Java項目中的使用詳解_java

Http協議的重要性相信不用我多說了，HttpClient相比傳統JDK內建的URLConnection，增加了易用性和靈活性（具體區別，日後我們再討論），它不僅是用戶端發送Http請求變得容易，而且也方便了開發人員測試介面（基於Http協議的），即提高了開發的效率，也方便提高代碼的健壯性。因此熟練掌握HttpClient是很重要的必修內容，掌握HttpClient後，相信對於Http協議的瞭解會更加深入。

一、簡介

HttpClient是Apache Jakarta Common下的子項目，用來提供高效的、最新的、功能豐富的支援HTTP協議的用戶端編程工具包，並且它支援HTTP協議最新的版本和建議。HttpClient已經應用在很多的項目中，比如Apache Jakarta上很著名的另外兩個開源項目Cactus和HTMLUnit都使用了HttpClient。

下載地址: http://hc.apache.org/downloads.cgi

二、特性

1. 基於標準、純淨的java語言。實現了Http1.0和Http1.1
2. 以可擴充的物件導向的結構實現了Http全部的方法（GET, POST, PUT, DELETE, HEAD, OPTIONS, and TRACE）。
3. 支援HTTPS協議。
4. 通過Http代理建立透明的串連。
5. 利用CONNECT方法通過Http代理建立隧道的https串連。
6. Basic, Digest, NTLMv1, NTLMv2, NTLM2 Session, SNPNEGO/Kerberos認證方案。
7. 外掛程式式的自訂認證方案。
8. 便攜可靠的通訊端工廠使它更容易的使用第三方解決方案。
9. 連線管理員支援多線程應用。支援設定最大串連數，同時支援設定每個主機的最大串連數，發現並關閉到期的串連。
10. 自動處理Set-Cookie中的Cookie。
11. 外掛程式式的自訂Cookie策略。
12. Request的輸出資料流可以避免流中內容直接緩衝到socket伺服器。
13. Response的輸入資料流可以有效從socket伺服器直接讀取相應內容。
14. 在http1.0和http1.1中利用KeepAlive保持持久串連。
15. 直接擷取伺服器發送的response code和 headers。
16. 設定連線逾時的能力。
17. 實驗性的支援http1.1 response caching。
18. 原始碼基於Apache License 可免費擷取。

三、使用方法

使用HttpClient發送請求、接收響應很簡單，一般需要如下幾步即可。

1. 建立HttpClient對象。

2. 建立要求方法的執行個體，並指定請求URL。如果需要發送GET請求，建立HttpGet對象；如果需要發送POST請求，建立HttpPost對象。

3. 如果需要發送請求參數，可調用HttpGet、HttpPost共同的setParams(HetpParams params)方法來添加請求參數；對於HttpPost對象而言，也可調用setEntity(HttpEntity entity)方法來佈建要求參數。

4. 調用HttpClient對象的execute(HttpUriRequest request)發送請求，該方法返回一個HttpResponse。

5. 調用HttpResponse的getAllHeaders()、getHeaders(String name)等方法可擷取伺服器的回應標頭；調用HttpResponse的getEntity()方法可擷取HttpEntity對象，該對象封裝了伺服器的響應內容。程式可通過該對象擷取伺服器的響應內容。

6. 釋放串連。無論執行方法是否成功，都必須釋放串連

四、執行個體

package com.test; import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.io.UnsupportedEncodingException; import java.security.KeyManagementException; import java.security.KeyStore; import java.security.KeyStoreException; import java.security.NoSuchAlgorithmException; import java.security.cert.CertificateException; import java.util.ArrayList; import java.util.List; import javax.net.ssl.SSLContext; import org.apache.http.HttpEntity; import org.apache.http.NameValuePair; import org.apache.http.ParseException; import org.apache.http.client.ClientProtocolException; import org.apache.http.client.entity.UrlEncodedFormEntity; import org.apache.http.client.methods.CloseableHttpResponse; import org.apache.http.client.methods.HttpGet; import org.apache.http.client.methods.HttpPost; import org.apache.http.conn.ssl.SSLConnectionSocketFactory; import org.apache.http.conn.ssl.SSLContexts; import org.apache.http.conn.ssl.TrustSelfSignedStrategy; import org.apache.http.entity.ContentType; import org.apache.http.entity.mime.MultipartEntityBuilder; import org.apache.http.entity.mime.content.FileBody; import org.apache.http.entity.mime.content.StringBody; import org.apache.http.impl.client.CloseableHttpClient; import org.apache.http.impl.client.HttpClients; import org.apache.http.message.BasicNameValuePair; import org.apache.http.util.EntityUtils; import org.junit.Test; public class HttpClientTest {   @Test   public void jUnitTest() {     get();   }   /**    * HttpClient串連SSL    */   public void ssl() {     CloseableHttpClient httpclient = null;     try {       KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());       FileInputStream instream = new FileInputStream(new File("d:\\tomcat.keystore"));       try {         // 載入keyStore d:\\tomcat.keystore          trustStore.load(instream, "123456".toCharArray());       } catch (CertificateException e) {         e.printStackTrace();       } finally {         try {           instream.close();         } catch (Exception ignore) {         }       }       // 相信自己的CA和所有自簽名的認證       SSLContext sslcontext = SSLContexts.custom().loadTrustMaterial(trustStore, new TrustSelfSignedStrategy()).build();       // 只允許使用TLSv1協議       SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslcontext, new String[] { "TLSv1" }, null,           SSLConnectionSocketFactory.BROWSER_COMPATIBLE_HOSTNAME_VERIFIER);       httpclient = HttpClients.custom().setSSLSocketFactory(sslsf).build();       // 建立http請求(get方式)       HttpGet httpget = new HttpGet("https://localhost:8443/myDemo/Ajax/serivceJ.action");       System.out.println("executing request" + httpget.getRequestLine());       CloseableHttpResponse response = httpclient.execute(httpget);       try {         HttpEntity entity = response.getEntity();         System.out.println("----------------------------------------");         System.out.println(response.getStatusLine());         if (entity != null) {           System.out.println("Response content length: " + entity.getContentLength());           System.out.println(EntityUtils.toString(entity));           EntityUtils.consume(entity);         }       } finally {         response.close();       }     } catch (ParseException e) {       e.printStackTrace();     } catch (IOException e) {       e.printStackTrace();     } catch (KeyManagementException e) {       e.printStackTrace();     } catch (NoSuchAlgorithmException e) {       e.printStackTrace();     } catch (KeyStoreException e) {       e.printStackTrace();     } finally {       if (httpclient != null) {         try {           httpclient.close();         } catch (IOException e) {           e.printStackTrace();         }       }     }   }   /**    * post方式提交表單（類比使用者登入請求）    */   public void postForm() {     // 建立預設的httpClient執行個體.      CloseableHttpClient httpclient = HttpClients.createDefault();     // 建立httppost      HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");     // 建立參數隊列      List<namevaluepair> formparams = new ArrayList<namevaluepair>();     formparams.add(new BasicNameValuePair("username", "admin"));     formparams.add(new BasicNameValuePair("password", "123456"));     UrlEncodedFormEntity uefEntity;     try {       uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");       httppost.setEntity(uefEntity);       System.out.println("executing request " + httppost.getURI());       CloseableHttpResponse response = httpclient.execute(httppost);       try {         HttpEntity entity = response.getEntity();         if (entity != null) {           System.out.println("--------------------------------------");           System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));           System.out.println("--------------------------------------");         }       } finally {         response.close();       }     } catch (ClientProtocolException e) {       e.printStackTrace();     } catch (UnsupportedEncodingException e1) {       e1.printStackTrace();     } catch (IOException e) {       e.printStackTrace();     } finally {       // 關閉串連,釋放資源        try {         httpclient.close();       } catch (IOException e) {         e.printStackTrace();       }     }   }   /**    * 發送 post請求訪問本地應用並根據傳遞參數不同返回不同結果    */   public void post() {     // 建立預設的httpClient執行個體.      CloseableHttpClient httpclient = HttpClients.createDefault();     // 建立httppost      HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");     // 建立參數隊列      List<namevaluepair> formparams = new ArrayList<namevaluepair>();     formparams.add(new BasicNameValuePair("type", "house"));     UrlEncodedFormEntity uefEntity;     try {       uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");       httppost.setEntity(uefEntity);       System.out.println("executing request " + httppost.getURI());       CloseableHttpResponse response = httpclient.execute(httppost);       try {         HttpEntity entity = response.getEntity();         if (entity != null) {           System.out.println("--------------------------------------");           System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));           System.out.println("--------------------------------------");         }       } finally {         response.close();       }     } catch (ClientProtocolException e) {       e.printStackTrace();     } catch (UnsupportedEncodingException e1) {       e1.printStackTrace();     } catch (IOException e) {       e.printStackTrace();     } finally {       // 關閉串連,釋放資源        try {         httpclient.close();       } catch (IOException e) {         e.printStackTrace();       }     }   }   /**    * 發送 get請求    */   public void get() {     CloseableHttpClient httpclient = HttpClients.createDefault();     try {       // 建立httpget.        HttpGet httpget = new HttpGet("http://www.baidu.com/");       System.out.println("executing request " + httpget.getURI());       // 執行get請求.        CloseableHttpResponse response = httpclient.execute(httpget);       try {         // 擷取響應實體          HttpEntity entity = response.getEntity();         System.out.println("--------------------------------------");         // 列印響應狀態          System.out.println(response.getStatusLine());         if (entity != null) {           // 列印響應內容長度            System.out.println("Response content length: " + entity.getContentLength());           // 列印響應內容            System.out.println("Response content: " + EntityUtils.toString(entity));         }         System.out.println("------------------------------------");       } finally {         response.close();       }     } catch (ClientProtocolException e) {       e.printStackTrace();     } catch (ParseException e) {       e.printStackTrace();     } catch (IOException e) {       e.printStackTrace();     } finally {       // 關閉串連,釋放資源        try {         httpclient.close();       } catch (IOException e) {         e.printStackTrace();       }     }   }   /**    * 上傳檔案    */   public void upload() {     CloseableHttpClient httpclient = HttpClients.createDefault();     try {       HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceFile.action");       FileBody bin = new FileBody(new File("F:\\image\\sendpix0.jpg"));       StringBody comment = new StringBody("A binary file of some kind", ContentType.TEXT_PLAIN);       HttpEntity reqEntity = MultipartEntityBuilder.create().addPart("bin", bin).addPart("comment", comment).build();       httppost.setEntity(reqEntity);       System.out.println("executing request " + httppost.getRequestLine());       CloseableHttpResponse response = httpclient.execute(httppost);       try {         System.out.println("----------------------------------------");         System.out.println(response.getStatusLine());         HttpEntity resEntity = response.getEntity();         if (resEntity != null) {           System.out.println("Response content length: " + resEntity.getContentLength());         }         EntityUtils.consume(resEntity);       } finally {         response.close();       }     } catch (ClientProtocolException e) {       e.printStackTrace();     } catch (IOException e) {       e.printStackTrace();     } finally {       try {         httpclient.close();       } catch (IOException e) {         e.printStackTrace();       }     }   } }</namevaluepair></namevaluepair></namevaluepair></namevaluepair> 

本執行個體是採用HttpClient4.3最新版本。該版本與之前的代碼寫法風格相差較大，大家多留意下。