servlet实现任何格式文件下载

/**//*
 * Generated by MyEclipse Struts
 * Template path: templates/java/JavaClass.vtl
 */
package com.snet.view.action;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;

/** *//** 
 * MyEclipse Struts
 * Creation date: 05-07-2008
 * 
 * XDoclet definition:
 * @struts.action
 */
public class DownloadFileAction extends Action ...{
    /**//*
     * Generated Methods
     */

    /** *//** 
     * Method execute
     * @param mapping
     * @param form
     * @param request
     * @param response
     * @return ActionForward
     * @throws IOException 
     * @throws IOException 
     */
    public ActionForward execute(ActionMapping mapping, ActionForm form,
            HttpServletRequest request, HttpServletResponse response)...{
        //get the name of file to download or read
        String fileName=request.getParameter("fileName");
        response.setContentType("application/OCTET-STREAM;charset=gb2312");
        response.setHeader("Content-Disposition", "attachment;filename="+fileName);
        String context=request.getSession().getServletContext().getRealPath("");
        File file=new File(context+"/uploadFiles/"+fileName);
        FileInputStream fis = null;
        BufferedOutputStream out=null;
        try
        ...{
            fis = new FileInputStream(file);
            out = new BufferedOutputStream(response.getOutputStream());
            byte[] buffer=new byte[1024];
            int len;
            while((len=fis.read(buffer))!=-1)...{//read from the file on server
                out.write(buffer, 0, len);      //write to client
                out.flush();
            }
        } catch (FileNotFoundException e)
        ...{
            try
            ...{
                /**//*
                 * Clears any data that exists in the buffer as well 
                 * as the status code and headers
                 */
                response.reset();
                /**//*set content type once again*/
                response.setContentType("text/html;charset=gb2312");
                /**//*give error message to client*/
                response.getWriter().println("文件未找到");
            } catch (IOException e1)
            ...{
                e1.printStackTrace();
            }
            e.printStackTrace();
        } catch (IOException e)
        ...{
            e.printStackTrace();
        }finally...{
            try
            ...{
                if(fis!=null)...{
                    fis.close();
                }
                if(out!=null)...{
                    out.close();
                }
            } catch (IOException e)
            ...{
                e.printStackTrace();
            }
        }
        return null;
    }
}