username为空时，为什么也能注册，但第二次就不会了

下面是Register源码，老师看下再哪里修改

package com.imooc.servlet;

import java.io.FileOutputStream;

/**

 * Servlet implementation class RegistServlet

 */

@WebServlet("/RegistServlet")

public class RegistServlet extends HttpServlet {

private static final long serialVersionUID = 1L;

/**

* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse

*      response)

*/

protected void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

// 数据的接收

// 文件上传基本操作

// 注意包要导入commons那个

boolean flag = true;

Map<String, String> map = new HashMap<String, String>();

String url = null;

try {

// 1.创建一个磁盘文件项工厂对象

DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory();

// 2.创建一个核心解析类

ServletFileUpload servletFileUpload = new ServletFileUpload(diskFileItemFactory);

// 3.解析request请求，返回的是List集合,List集合存放的是FileItem对象

List<FileItem> list = servletFileUpload.parseRequest(request);

// 3.1定义一个List集合用于保存兴趣爱好

List<String> hobbylist = new ArrayList<String>();

// 4.遍历结合，获得每个FileItem,判断是表单还是文件上传项

for (FileItem fileItem : list) {

if (fileItem.isFormField()) {

// 普通表单项

// 接收表单项参数的值

String name = fileItem.getFieldName(); // 获取name

String value = fileItem.getString("UTF-8"); // 获取name对应的值，且避免中文乱码问题

System.out.println(name + "   " + value);

// 接收表单多项参数的值

if ("hobby".equals(name)) {

String hobbyValue = fileItem.getString("UTF-8");

hobbylist.add(hobbyValue);

// 删除两边的大括号

hobbyValue = hobbylist.toString().substring(1, hobbylist.toString().length() - 1);

System.out.println(name + "   " + hobbyValue);

// 存放表单多项

map.put(name, hobbyValue);

} else {

// 存放表单项

map.put(name, value);

}

} else {

// 文件上传项

// 文件上传功能

// 获得文件上传的名称；

String fileName = fileItem.getName(); // 获取name对应的值

// 设置条件：用户名不为空的时候才能文件上传

if (fileName != null && !"".equals(fileName)) {

// 通过工具类完成唯一文件名

String uuidFlieName = UploadUtils.getUUIDFileName(fileName);

// 获得文件上传的数据

InputStream is = fileItem.getInputStream();

// 获取文件上传的路径：

String path = this.getServletContext().getRealPath("/upload");

// 将输入流对接到输出流

url = path + "\\" + uuidFlieName;

OutputStream os = new FileOutputStream(url);

int length = 0;

byte[] b = new byte[1024];

while ((length = is.read(b)) != -1) {

os.write(b, 0, length);

}

is.close();

os.close();

}

}

}

System.out.println(map);

List<User> userList = (List<User>) this.getServletContext().getAttribute("list");

// 判断是否有相同的用户存在

for (User u : userList) {

if (u.getUsername().equals(map.get("username"))) {

request.setAttribute("msg", "用户名已经存在");

// 这时要返回注册页面，重新注册 请求转发无需再添加上文路径，

// 直接写WebContent下面的路径

request.getRequestDispatcher("/regist.jsp").forward(request, response);

return;

}

}

// 把Map数据封装到User里面，保存起来

User user = new User();

user.setUsername(map.get("username"));

user.setPassword(map.get("password"));

user.setNickname(map.get("nickname"));

user.setSex(map.get("sex"));

user.setHobby(map.get("hobby"));

user.setPath(url);

userList.add(user);

// 遍历，检查新的user有无放进去

for (User u : userList) {

System.out.println(u);

}

// 添加新的user后，再把它放回去

this.getServletContext().setAttribute("list", userList);

// 注册成功，跳转到登录页面(重定向，会重新发送一次请求，改变了http路径，但不能携带参数。如果是请求转发则不会改变且不会在发送一次，可以携带参数)

request.getSession().setAttribute("username", user.getUsername());

response.sendRedirect(request.getContextPath() + "/login.jsp");

// request.getRequestDispatcher("/login.jsp").forward(request, response);

} catch (FileUploadException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

/**

* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse

*      response)

*/

protected void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

// TODO Auto-generated method stub

doGet(request, response);

}

}