Method for jsp to Download Servlet File

This paper describes the method of downloading Servlet files by jsp. Share it for your reference. The details are as follows:

package com;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLEncoder;
import java.util.Date;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import com.sun.xml.internal.messaging.saaj.packaging.mime.internet.MimeUtility;
/**
 *  File download class. To prevent the client browser from opening the target file directly (for example, when installing the MS Office Suite of Windows In IE The browser may be directly in the IE Open what you want to download in the browser doc Or xls File), add the forced download in the response header MIME Type. 
 */
public class DownloadFile extends HttpServlet {
  private static final Log log = LogFactory.getLog(DownloadFile.class);
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException {
    long timeStart = 0;
    if(log.isDebugEnabled()){
      timeStart=System.currentTimeMillis();
    }
    response.setContentType("application/x-download charset=UTF-8");
    java.io.FileInputStream fis = null;
    String filepath = request.getRealPath("");
    javax.servlet.ServletOutputStream sos = null;
    // System.out.println("DownloadFile filename:" + filename);
    try {
      if(request.getParameter("filename")==null
          ||request.getParameter("showName")==null){
        return;
      }
      String filename = request.getParameter("filename");
      String showName = request.getParameter("showName");
      request.setCharacterEncoding("UTF-8");
      response.setCharacterEncoding("UTF-8");
      java.io.File file = new java.io.File(filepath + filename);
      if (!file.exists()) {
        log.error(file.getAbsolutePath() + "  File does not exist !");
        return;
      }
      //  Read file stream 
      fis = new java.io.FileInputStream(file);
      //  Set the file name for download and save 
      sos = response.getOutputStream();
      showName += filename.substring(filename.lastIndexOf("."));
      String contentDisposition = "", browser = getBrowser(request);
      if ("IE".equals(browser)) {
        contentDisposition = "attachment; filename=" + URLEncoder.encode(showName, "UTF-8").replace("+", "%20");
      } else if ("CH".equals(browser)) {
        contentDisposition = "attachment; filename=" + MimeUtility.encodeText(showName, "UTF8", "B");
      } else if ("SF".equals(browser)) {
        contentDisposition = "attachment; filename=" + new String(showName.getBytes("UTF-8"), "ISO8859-1");
      } else {
        contentDisposition = "attachment; filename*=UTF-8''" + URLEncoder.encode(showName, "UTF-8").replace("+", "%20");
      }
      response.setHeader("Content-Disposition", contentDisposition);
      int byteCount = 0; 
      if (fis != null) {
        byte[] buff = new byte[1024];
        int bytesRead;
        while(-1 != (bytesRead = fis.read(buff, 0, buff.length))) {
          sos.write(buff, 0, bytesRead);
          sos.flush();
          byteCount += bytesRead;
        } 
      }
      sos.flush();
      if(log.isDebugEnabled()){
        log.debug(" File download complete, file size: "+ byteCount +" Total time spent :"+ (new Date().getTime() - timeStart) +" Milliseconds. ");
      }
    } catch(IOException ioe) {
      ioe.printStackTrace();
    } finally {
      try {
        if(fis!=null){
          fis.close();
        }
      } catch (IOException e) {
      } finally {
        try {
          if(sos!=null){
            sos.close();
          }
        } catch (IOException e) {
        }
      }
    }
  }
  public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    out.println("<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\">");
    out.println("<html>");
    out.println(" <head>");
    out.println("  <title> File download </title>");
    out.println("  <meta http-equiv=\"Content-Type\" content=\"text/html; charset=UTF-8\" />");
    out.println(" </head>");
    out.println(" <body>");
    out.print(" This is ");
    out.print(this.getClass().getName());
    out.println(", using the POST method");
    out.println(" </body>");
    out.println("</html>");
    out.flush();
    out.close();
  }
  private String getBrowser(HttpServletRequest request) {
    String userAgent = request.getHeader("USER-AGENT").toLowerCase();
    if (userAgent != null) {
      if (userAgent.indexOf("msie") >= 0) {
        return "IE";
      } else if (userAgent.indexOf("mozilla") >= 0) {
        return "FF";
      } else if (userAgent.indexOf("applewebkit") >= 0) {
        return "CH";
      } else if (userAgent.indexOf("safari") >= 0) {
        return "SF";
      } else if (userAgent.indexOf("opera") >= 0) {
        return "OP";
      }
    }
    return null;
  }
}

I hope this article is helpful to everyone's JSP programming.