response.setContentType("application/octet-stream");
            response.setContentType("application/OCTET-STREAM;charset=UTF-8");
            response.setHeader("Content-Disposition", "attachment;filename=" + fileName1);

File file = new File(filePath + fileName);

try {
    fis = new FileInputStream(file);
    out = new BufferedOutputStream(response.getOutputStream());
    byte[] buffer = new byte[1024];
    int len;
    while ((len = fis.read(buffer)) != -1) {
         out.write(buffer, 0, len);
         out.flush();
    }
}catch.......
 

一種線上開啟或下載的方式

public String executeCommandUDownload(ActionContext context)throws Exception{
		HttpServletResponse response = context.getResponse();
		response.setCharacterEncoding("UTF-8");
		boolean isOnLine = false;
		String fileName = context.getRequest().getParameter("fileName");
		
                Connection con = null;
		HttpServletRequest request = context.getRequest();
		String filePath = null;
		BufferedInputStream buffer=null;
		OutputStream out=null;
		try
		{
			con = this.getConnection(context);
			if("".equals(fileName) || fileName == null){
				FileInfoBean bean = new FileInfoBean();
				fileName = bean.findName(con, id);
				
			}
			
			
			
			File f = new File(filePath);
                      //檢查該檔案是否存在
			if(!f.exists()){
				response.sendError(404,"File not found!");
				return "File not found!";
			}
			buffer = new BufferedInputStream(new FileInputStream(f));
			byte[] buf = new byte[1024];
			int len = 0;
		
			response.reset(); //非常重要
			if(isOnLine){ //線上開啟方式
				URL u = new URL("file:///"+filePath);
				response.setContentType(u.openConnection().getContentType());
				response.setHeader("Content-Disposition", "inline; filename="+(f.getName()).getBytes("gbk"));
			//檔名應該編碼成UTF-8
			}
			else{ //純下載方式

				response.setContentType("application/x-msdownload"); 
				
				response.setHeader("Content-Disposition", "attachment; filename=" + java.net.URLEncoder.encode(f.getName(),"UTF-8")); 
				
			}
			out = response.getOutputStream();
			while((len = buffer.read(buf)) >0)
				out.write(buf,0,len);
		}catch(Throwable e)
		{
			e.printStackTrace();
		}finally
		{
			try
			{
				buffer.close();
				out.close();
			}catch(Throwable e)
			{
				e.printStackTrace();   
			}
		}
		return "";
	}