servlet实现文件下载的实用类分享

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;

/**
 * 文件下载类。为了防止客户端浏览器直接打开目标文件（例如在装了MS Office套件的Windows中的IE浏览器可能就会直接在IE浏览器中打开你想下载的doc或者xls文件），在响应头里加入强制下载的MIME类型。
 */
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() + " 文件不存在!");
    return;
   }
   // 读取文件流
   fis = new java.io.FileInputStream(file);
   // 设置下载保存的文件名
   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("文件下载完成，文件大小："+ byteCount +"，总共用时:"+ (new Date().getTime() - timeStart) +"毫秒。");
   }
  } 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>文件下载/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;
 }
}