Servlet实现代理文件下载功能

<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> 

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 
 } 
 
}