Servlet 文件下载

@WebServlet("/servletload")

public class Servletload extends HttpServlet {

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {

        //1. 获取请求参数，文件名称

        String file = req.getParameter("filename");

        //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: 代表整个 web 应用，可以对服务器通信

        ServletContext context = this.getServletContext();

        //realpath: 获取文件服务器路径:/opt/idea/ideaDemo/day12_1/out/artifacts/day12_1_war_exploded/image/tupian.jpg

        String filerealpath = context.getRealPath("/image/"+file);

        System.out.println(filerealpath);

        //2.2 使用字节流关联

        FileInputStream input = new FileInputStream(filerealpath);

        //3. 设置 response 的响应头

        //3.1 获取 MIME 类型

        String mime = context.getMimeType(file);

        //3.2 设置响应头类型 content-type: 服务器告诉客户端本次响应体格式以及编码

        resp.setHeader("content-type",mime);

        // 解决中文文件名乱码问题

        //1. 获取 user-agent 请求头 user-agent: 浏览器告诉服务器访问时使用的浏览器版本信息，可以解决浏览器的兼容性问题

        String user_agent = req.getHeader("user-agent");

        //2. 使用工具类编码即可

        file = DownLoadUtils.getFileName(user_agent,file);

        //3.3 设置响应头打开方式，解释如下 PS

        resp.setHeader("content-disposition","attachment;filename="+"/image/"+file);

        //4. 将输入流的数据写出到输出流中

        ServletOutputStream out = resp.getOutputStream();

        int i = 0;

        byte[] by = new byte[1024 * 8];

        while((i = input.read(by)) != -1){

            out.write(by,0,i);

        }

        // 关闭流

        input.close();

        out.close();

    }

    protected void doGet(HttpServletRequest req,HttpServletResponse resp) throws IOException {

        this.doPost(req,resp);

        int i = 0;

    }

}

public class DownLoadUtils {

    public static String getFileName(String agent,String filename) throws UnsupportedEncodingException {

        if(agent.contains("MSIE")){

            //IE 浏览器

            filename = URLEncoder.encode(filename,"utf-8");

            filename = filename.replace("+"," ");

        }else if(agent.contains("Firefox")){

            // 火狐浏览器

            BASE64Encoder base64encoder = new BASE64Encoder();

            filename = "?utf-8?B?" + base64encoder.encode(filename.getBytes("utf-8"))+"?=";

        }else{

            // 其它浏览器

            filename = URLEncoder.encode(filename,"utf-8");

        }

        return filename;

    }

}