javaweb下载

 //1.获取请求参数，文件名称
        String filename = request.getParameter("filename");
        response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out.flush();
		out.close();
        if (filename=="") {
        	 
		}else {
			 //2.使用字节输入流加载文件进内存
	        //2.1找到文件服务器路径
	        ServletContext servletContext = this.getServletContext();
	        String realPath = servletContext.getRealPath("/upload/" + filename);
	        //2.2用字节流关联
	        FileInputStream fis = new FileInputStream(realPath);
	 
	        //3.设置response的响应头
	        //3.1设置响应头类型：content-type
	        String mimeType = servletContext.getMimeType(filename);//获取文件的mime类型
	        response.setHeader("content-type",mimeType);
	        //3.2设置响应头打开方式:content-disposition
	 
	        //解决中文文件名问题
	        //1.获取user-agent请求头、
	        String agent = request.getHeader("user-agent");
	        //2.使用工具类方法编码文件名即可
	        filename = DownLoadUtils.getFileName(agent, filename);
	 
	        response.setHeader("content-disposition","attachment;filename="+filename);
	        //4.将输入流的数据写出到输出流中
	        ServletOutputStream sos = response.getOutputStream();
	        byte[] buff = new byte[1024 * 8];
	        int len = 0;
	        while((len = fis.read(buff)) != -1){
	            sos.write(buff,0,len);
	        }
	        fis.close();
	        out.flush();
    		out.close();