java实现文件上传和下载

<form method="post" action="/user/regist" enctype="multipart/form-data">
        <table style="border: chartreuse;solid:2px">
            <tr>
                <th>用户名</th>
                <td><input type="text" name="username"></td>
            </tr>
            <tr>
                <th>密码</th>
                <td><input type="password" name="password"></td>
            </tr>
            <tr>
                <th>用户头像</th>
                <td><input type="file" name="photo"> </td>
            </tr>
            <tr>
                <td colspan="2"><input type="submit" value="提交"></td>
            </tr>
        </table>
</form>

@WebServlet(value = "/user/regist")
public class UploadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //创建一个工厂对象
        DiskFileItemFactory factory = new DiskFileItemFactory();
        //创建一个多部件解析器对象
        ServletFileUpload fileUpload = new ServletFileUpload(factory);
        User user = new User();
        FileOutputStream out=null;
        try {
            //用解析器对象解析请求，返回一个FileItem类型的集合
            List<FileItem> list = fileUpload.parseRequest(req);
            for (FileItem fileItem : list) {
                /**
                 * fileItem.getFieldName());:::获取组件的name值
                 * fileItem.getName());::::获取文件域的文件名
                 * fileItem.getSize());::::获取数据的字节个数
                 * fileItem.getString());::::获取数据的字符串
                 * fileItem.isFormField());:::判断是否为普通组件
                 */
                //判断部件是否为普通组件
                if (fileItem.isFormField()) {//普通组件
                    //获取组件名字也就是name的值
                    String fieldName = fileItem.getFieldName();
                    //获取组件的值也就是value的值
                    String value = fileItem.getString("utf-8");
                    if ("username".equals(fieldName)) { //设置实体类的属性
                        user.setUsername(value);
                    } else if ("password".equals(fieldName)) {
                        user.setPassword(value);
                    }
                } else {// 文件域
                    //获取文件名
                    String fielName = fileItem.getName();
                    //输入流来读数据
                    InputStream in = fileItem.getInputStream();
                    //设置文件写出的路径，并用随机码来保证图片可以重复
                    String path=req.getServletContext().getRealPath("/imgs/"+ UUID.randomUUID()+fielName);
                    System.out.println("文件路径为："+path);
                    File file = new File(path);
                     out = new FileOutputStream(file);
                     //利用commons-io-1.4.jar的IOUtils的copy方法直接实现文件的复制
                    IOUtils.copy(in,out);
                    user.setPhoto(file.getName());
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if(out!=null){
                out.close();
            }
        }
        req.getSession().setAttribute("user",user);
        req.getRequestDispatcher("/sucess.jsp").forward(req,resp);
    }
 
}

@WebServlet("/user/download")
public class DownloadServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        //获取要下载的文件名
        String fileName = request.getParameter("fileName");
        System.out.println(fileName);
        //获取服务器中存储图片的文件夹的路径
        String path1 = request.getServletContext().getRealPath("/imgs");
        String path=path1+"/"+fileName;
        File file = new File(path);
        //创建输入流读文件
        FileInputStream in = new FileInputStream(file);
        //通过文件名字获取文件的大类型
        String type = request.getServletContext().getMimeType(fileName);
        //设置响应头ContentType指定响应内容的类型
        response.setHeader("Content-type",type);
        //设置响应头Content-Disposition 指定以附件形式保存响应的信息
        response.setHeader("Content-Disposition","attachment;filename="+(URLEncoder.encode(fileName, "utf-8")));
        ServletOutputStream out = response.getOutputStream();
        //实现文件的读写
        IOUtils.copy(in,out);
        if(in!=null){
        in.close();
        }
    }
}