Servlet实现代理文件下载功能_Java教程

用户向代理服务器发送请求，代理服务器从后端服务器上获取文件，并返回给用户
web.xml:

									<servlet> 

									 <servlet-name>BigFile</servlet-name> 

									 <servlet-class>cn.ac.dsp.servlet.BigFile</servlet-class> 

									</servlet> 

									 <servlet-mapping> 

									 <servlet-name>BigFile</servlet-name> 

									 <url-pattern>*.ts</url-pattern> 

									</servlet-mapping>

servlet:

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									package cn.ac.dsp.servlet; 

									import java.io.IOException; 

									import java.io.InputStream; 

									import java.io.PrintWriter; 

									import java.io.StringWriter; 

									import javax.servlet.ServletException; 

									import javax.servlet.ServletOutputStream; 

									import javax.servlet.http.HttpServlet; 

									import javax.servlet.http.HttpServletRequest; 

									import javax.servlet.http.HttpServletResponse; 

									import org.apache.http.HttpEntity; 

									import org.apache.http.HttpResponse; 

									import org.apache.http.client.ClientProtocolException; 

									import org.apache.http.client.HttpClient; 

									import org.apache.http.client.methods.HttpGet; 

									import org.apache.http.impl.client.DefaultHttpClient; 

									import org.apache.http.params.CoreConnectionPNames; 

									import org.apache.http.params.CoreProtocolPNames; 

									import org.apache.log4j.Logger; 

									import cn.ac.dsp.common.Constant; 

									import cn.ac.dsp.common.SystemParameters; 

									/** 

									 * 给静态大文件提供服务的servlet 

									 */

									public class BigFile extends HttpServlet { 

									 private static final long serialVersionUID = 1L; 

									 private static final Logger log = Logger.getLogger(BigFile.class); 

									 /** 

									  * @see HttpServlet#HttpServlet() 

									  */

									 public BigFile() { 

									  super(); 

									  // TODO Auto-generated constructor stub 

									 } 

									 /** 

									  * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 

									  */

									 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 

									  log.info("request for bigfile"); 

									  long startTime = System.nanoTime(); 

									  String requestUrl = request.getRequestURI(); 

									  //请求的文件名 

									  String filename = requestUrl.substring(requestUrl.lastIndexOf("/")); 

									  HttpClient httpClient = new DefaultHttpClient(); 

									  httpClient.getParams().setParameter(CoreConnectionPNames.CONNECTION_TIMEOUT, Constant.HttpConnTimeOut); 

									  httpClient.getParams().setParameter(CoreConnectionPNames.SO_TIMEOUT, Constant.SoConnTimeOut); 

									  httpClient.getParams().setParameter(CoreProtocolPNames.HTTP_CONTENT_CHARSET, "UTF-8"); 

									  //后端服务器的IP 

									  String serverIP = "192.168.101.190"; 

									  //后端服务器的文件地址 

									  StringBuilder backUrl = new StringBuilder(); 

									  backUrl.append("http://"); 

									  backUrl.append(serverIP); 

									  backUrl.append("/LBA/bigfile/"); 

									  backUrl.append(filename); 

									  HttpGet httpGet = new HttpGet(backUrl.toString()); 

									  httpGet.getParams().setParameter(CoreProtocolPNames.HTTP_CONTENT_CHARSET, "UTF-8"); 

									  log.info("distribute bigfile to " + backUrl.toString()); 

									  HttpResponse backResponse; 

									  try { 

									   backResponse = httpClient.execute(httpGet); 

									//   log.info(backResponse.getParams().getParameter(CoreProtocolPNames.HTTP_CONTENT_CHARSET)); 

									   HttpEntity httpEntity = backResponse.getEntity(); 

									   InputStream in = httpEntity.getContent(); 

									//   BufferedReader br = new BufferedReader(new InputStreamReader(httpEntity.getContent(), "UTF-8")); 

									   byte[] buf = new byte[4096]; 

									   int readLength; 

									   response.setCharacterEncoding("UTF-8"); 

									   ServletOutputStream out = response.getOutputStream(); 

									   while((readLength = in.read(buf)) != -1){ 

									    out.write(buf, 0, readLength); 

									   }  

									   in.close(); 

									   out.flush(); 

									   out.close(); 

									  } catch (ClientProtocolException e) { 

									   StringWriter sw = new StringWriter(); 

									   e.printStackTrace(new PrintWriter(sw)); 

									   log.error("ClientProtocolException when redirect bigfile. " + sw.toString());  

									  } catch (IOException e) { 

									   StringWriter sw = new StringWriter(); 

									   e.printStackTrace(new PrintWriter(sw)); 

									   log.error("IOException when redirect bigfile. " + sw.toString());  

									  } 

									  long endTime = System.nanoTime(); 

									  System.out.println("Response time: " + (endTime-startTime) + " ns"); 

									 } 

									 /** 

									  * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 

									  */

									 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 

									  // TODO Auto-generated method stub 

									 } 

									}