文件下载Servlet

mport cn.javass.ssonline.upload.util.UploadUtils; 
 
import java.io.*; 
import java.net.URLDecoder; 
import java.net.URLEncoder; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
 
public class DownloadServlet extends HttpServlet 
{ 
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
    throws ServletException, IOException 
  { 
    doPost(req, resp); 
  } 
 
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException 
  { 
    //只允许有一个参数 filename 
 
    String filename = new String(req.getQueryString().getBytes("ISO-8859-1"), "UTF-8").substring(9); 
    if ((filename == null) || (filename.trim().length() == 0) || (filename.contains("\\.\\."))) { 
      resp.setContentType("text/html;charset=utf-8"); 
      resp.getWriter().write("您下载的文件不存在！"); 
      return; 
    } 
    download(req, resp, filename); 
  } 
 
  private void download(HttpServletRequest request, HttpServletResponse response, String filename) 
  { 
    String userAgent = request.getHeader("User-Agent"); 
    boolean isIE = (userAgent != null) && (userAgent.toLowerCase().indexOf("msie") != -1); 
    try 
    { 
      filename = URLDecoder.decode(filename, "UTF-8"); 
 
      String filePath = UploadUtils.getUploadDir(request) + filename; 
 
      File file = new File(filePath); 
      if ((!(file.exists())) || (!(file.canRead()))) { 
        response.setContentType("text/html;charset=utf-8"); 
        response.getWriter().write("您下载的文件不存在！"); 
        return; 
      } 
      byte[] buf = new byte[1024]; 
      int len = 0; 
      BufferedInputStream br = null; 
      OutputStream ut = null; 
      response.reset(); 
 
      response.setHeader("Pragma", "No-cache"); 
      response.setHeader("Cache-Control", "must-revalidate, no-transform"); 
      response.setDateHeader("Expires", 0L); 
 
      String displayFilename = filename.substring(filename.lastIndexOf("_") + 1); 
      displayFilename = displayFilename.replace(" ", "_"); 
      response.setContentType("application/x-download"); 
 
      displayFilename = "[私塾在线学习网]"+displayFilename; 
      if (isIE) { 
        displayFilename = URLEncoder.encode(displayFilename, "UTF-8"); 
        response.setHeader("Content-Disposition", "attachment;filename=\"" + displayFilename + "\""); 
      } else { 
        displayFilename = new String(displayFilename.getBytes("UTF-8"), "ISO8859-1"); 
        response.setHeader("Content-Disposition", "attachment;filename=" + displayFilename); 
      } 
 
      br = new BufferedInputStream(new FileInputStream(file)); 
      ut = response.getOutputStream(); 
      while ((len = br.read(buf)) != -1) 
        ut.write(buf, 0, len); 
    } 
    catch (Exception e) { 
      e.printStackTrace(); 
    } 
  } 
}