用Servlet把文件写到Respond输出流里面供用户下载

    import java.io.*;  
    import java.net.*;  
    import javax.servlet.*;  
    import javax.servlet.http.*;  
    import javax.servlet.annotation.*;  
      
    @WebServlet(name = "download",urlPatterns = { "/download" })  
    public class download extends HttpServlet {  
        private static final long serialVersionUID = 1L;  
      
        protected void service(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException {  
            String filePath = this.getServletContext().getRealPath("/");// 获取真实路径  
            String downloadFilename = "中文是没有问题的.jpg";// 在下载框默认显示的文件名  
            downloadFilename = URLEncoder.encode(downloadFilename,"UTF-8");  
            // 对默认下载的文件名编码。不编码的结果就是，在客户端下载时文件名乱码  
            File file = new File(filePath + File.separator + "Chrysanthemum.jpg");  
            if (file.exists()) {  
                // 写明要下载的文件的大小  
                response.setContentLength((int) file.length());  
                response.setHeader("Content-Disposition","attachment;filename="  
                        + downloadFilename);// 设置在下载框默认显示的文件名  
                response.setContentType("application/octet-stream");// 指明response的返回对象是文件流  
                // 读出文件到response  
                // 这里是先需要把要把文件内容先读到缓冲区  
                // 再把缓冲区的内容写到response的输出流供用户下载  
                FileInputStream fileInputStream = new FileInputStream(file);  
                BufferedInputStream bufferedInputStream = new BufferedInputStream(  
                        fileInputStream);  
                byte[] b = new byte[bufferedInputStream.available()];  
                bufferedInputStream.read(b);  
                OutputStream outputStream = response.getOutputStream();  
                outputStream.write(b);  
                // 人走带门  
                bufferedInputStream.close();  
                outputStream.flush();  
                outputStream.close();  
            }  
        }  
    }