Servlet实现代理文件下载功能

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:

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
 } 

}

参考：一个文件下载的Servlet

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