Springframework - 在null上找不到属性或字段

【问题标题】：Springframework - property or field cannot be found on nullSpringframework - 在null上找不到属性或字段
【发布时间】：2018-03-31 00:39:51
【问题描述】：

我正在处理一个项目并不断收到错误消息。

<span style="font-style: italic;" th:text="${user != null} ? ${#strings.toUpperCase(user.username)} : 'user is null'"></span>

EL1007E: Property or field 'id' cannot be found on null

我是 thyemeleaf 和 spring 的新手，所以还在学习，所以不确定你需要什么来帮助解决这个问题，所以当我知道我需要提供什么时，我会更新。

登录/新用户模式所在的标题 HTML

<body>
  <div th:fragment="navbar">
    <div class="container">
      <nav class="navbar navbar-expand-lg navbar-dark bg-dark fixed-top">
        <a class="navbar-brand active" href="https://inplaydesign.com/index.html">d|b</a>
        <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
					<span class="navbar-toggler-icon"></span>
				</button>
        <div class="collapse navbar-collapse" id="navbarSupportedContent">
          <ul class="navbar-nav mr-auto">
            <li class="nav-item">
              <a class="nav-link" href="https://blog.inplaydesign.com">blog</a>
            </li>
            <li class="nav-item">
              <a class="nav-link" href="/gallery/gallery.html">gallery</a>
            </li>
            <li class="nav-item">
              <a class="nav-link" href="#">shop</a>
            </li>
            <li class="nav-item">
              <a class="nav-link" href="/faq/faq.html">f.a.q.</a>
            </li>
            <li class="nav-item">
              <a class="nav-link" href="/contact/contact.html">contact</a>
            </li>
          </ul>
          <button type="button" class="btn btn-outline-dark">
						<i class="fa fa-shopping-cart"></i> Shopping Cart
					</button>
          <button sec:authorize="isAnonymous()" type="button" class="btn btn-outline-dark" data-toggle="modal" data-target="#accountAccess">
						<i class="fa fa-id-card"></i> Account
					</button>
          <a sec:authorize="isAuthenticated()" th:href="@{/myProfile}">
            <button type="button" class="btn btn-outline-dark">
							<i class="fa fa-id-card"></i> Account
						</button>
          </a>
          <a sec:authorize="isAuthenticated()" th:href="@{/logout}">
            <button type="button" class="btn btn-outline-dark">
							<i class="fa fa-power-off"></i> log-out
						</button>
          </a>
        </div>
      </nav>
    </div>
    <!-- Account modal -->
    <div class="modal fade" id="accountAccess" tabindex="-1" role="dialog" aria-hidden="true">
      <div class="modal-dialog" role="document">
        <div class="modal-content">
          <div class="modal-header">
            <h5 class="modal-title">Account Login and Creation
            </h5>
          </div>
          <div class="modal-body">
            <ul class="nav nav-tabs" role="tablist">
              <li class="nav-item" th:classappend="${classActiveNewAccount}? 'active'">
                <a class="nav-link" data-toggle="tab" href="#tab-1" role="tab">Sign up</a>
              </li>
              <li class="nav-item" th:classappend="${classActiveLogin}? 'active'">
                <a class="nav-link active" data-toggle="tab" href="#tab-2" role="tab">User Login</a>
              </li>
              <li class="nav-item" th:classappend="${classActiveForgetPassword}? 'active'">
                <a class="nav-link" data-toggle="tab" href="#tab-3" role="tab">Forgot Password</a>
              </li>
            </ul>
            <div class="tab-content" style="margin-top: 10px;">
              <!-- New User -->
              <div class="tab-pane fade" id="tab-1" role="tabpanel" th:classappend="${classActiveNewAccount}? 'in active'">
                <form th:action="@{/newUser}" method="post">
                  <div class="container">
                    <div class="form-group">
                      <label for="email">Email Address</label>&nbsp;
                      <div class="alert alert-danger" th:if="${emailExists}">"Email already exists"</div>
                      <input type="email" class="form-control" id="email" name="email" placeholder="Enter Email Address" />
                    </div>
                    <div class="form-group">
                      <label for="NewUsername">Username</label>&nbsp;
                      <div class="alert alert-danger" th:if="${usernameExists}">"Username already exists"</div>
                      <input type="text" class="form-control" id="newUsername" name="NewUsername" tabindex="0" placeholder="Enter Username" />
                    </div>
                  </div>
                  <div class="modal-footer">
                    <button type="reset" class="btn btn-outline-dark btn-sm">
											<i class="fa fa-refresh"></i> Reset
										</button>
                    <button type="button" class="btn btn-outline-dark btn-sm">
											<i class="fa fa-user-plus"></i> Create New Account
										</button>
                  </div>
                </form>
              </div>

              <!-- login -->
              <div class="tab-pane fade show active" id="tab-2" role="tabpanel" th:classappend="${classActiveLogin}? 'active'">
                <div class="alert alert-danger" th:if="${param.error != null}">
                  <small>Please check your credentials and try again.</small>
                </div>
                <form th:action="@{/login}" method="post">
                  <div class="container">
                    <div class="form-group">
                      <label for="username">Username</label>
                      <input type="text" class="form-control" id="username" name="username" placeholder="Enter Username" />
                    </div>
                    <div class="form-group">
                      <label for="password">Password</label>
                      <input type="password" class="form-control" id="password" name="password" placeholder="Enter Password" />
                    </div>
                  </div>
                  <div class="modal-footer">
                    <button type="submit" class="btn btn-outline-dark btn-sm">
											<i class="fa fa-sign-in"></i> Log-In
										</button>
                  </div>
                </form>
              </div>

              <!-- Forgot password -->
              <div class="tab-pane fade" id="tab-3" role="tabpanel" th:classappend="${classActiveForgetPassword}? 'in active'">
                <div th:if="${emailNotExist}" class="alert alert-danger">Email does not exist</div>
                <div th:if="${forgetPasswordEmailSent}" class="alert alert-success">Please check your email for password reset token.</div>
                <form action="">
                  <div class="container">
                    <div class="form-group">
                      <label for="recoverEmail">User Email</label>
                      <input type="email" class="form-control" id="recoverEmail" placeholder="Enter Recovery Email" name="email" />
                    </div>
                  </div>
                  <div class="modal-footer">
                    <button type="submit" class="btn btn-outline-dark btn-sm">
											<i class="fa fa-external-link-square"></i> Submit
										</button>
                  </div>
                </form>
              </div>
            </div>
          </div>
        </div>
      </div>
    </div>
  </div>

  <div th:fragment="body-bottom-scripts">
    <!-- Optional JavaScript -->
    <!-- jQuery first, then Popper.js, then Bootstrap JS -->
    <script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" type="text/javascript"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.11.0/umd/popper.min.js" type="text/javascript"></script>
    <script src="/js/bootstrap.min.js" type="text/javascript"></script>
  </div>
</body>

import java.util.HashSet;
import java.util.Locale;
import java.util.Set;
import java.util.UUID;

import javax.servlet.http.HttpServletRequest;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.mail.SimpleMailMessage;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;

import com.digitalblasphemy.domain.User;
import com.digitalblasphemy.domain.security.PasswordResetToken;
import com.digitalblasphemy.domain.security.Role;
import com.digitalblasphemy.domain.security.UserRole;
import com.digitalblasphemy.service.UserService;
import com.digitalblasphemy.service.impl.UserSecurityService;
import com.digitalblasphemy.utility.MailConstructor;
import com.digitalblasphemy.utility.SecurityUtility;

@Controller
public class HomeController {

  @Autowired
  private JavaMailSender mailSender;

  @Autowired
  private MailConstructor mailConstructor;

  @Autowired
  private UserService userService;

  @Autowired
  private UserSecurityService userSecurityService;

  @RequestMapping("/")
  public String index() {
    return "index";
  }

  @RequestMapping("/myAccount")
  public String myAccount() {
    return "myAccount";
  }

  @RequestMapping("/login")
  public String login(Model model) {
    model.addAttribute("classActiveLogin", true);
    return "myProfile";
  }

  @RequestMapping("/forgetPassword")
  public String forgetPassword(
    HttpServletRequest request,
    @ModelAttribute("email") String email,
    Model model
  ) {
    model.addAttribute("classActiveForgetPassword", true);
    User user = userService.findByEmail(email);

    if (user == null) {
      model.addAttribute("emailNotExist", true);
      return "index";
    }

    String password = SecurityUtility.randomPassword();

    String encryptedPassword = SecurityUtility.passwordEncoder().encode(password);
    user.setPassword(encryptedPassword);

    userService.save(user);

    String token = UUID.randomUUID().toString();
    userService.createPasswordResetTokenForUser(user, token);

    String appUrl = "http://" + request.getServerName() + ":" + request.getServerPort() + request.getContextPath();

    SimpleMailMessage newEmail = mailConstructor.constructResetTokenEmail(appUrl, request.getLocale(), token, user, password);

    mailSender.send(newEmail);

    model.addAttribute("forgetPasswordEmailSent", "true");

    return "index";
  }

  @RequestMapping(value = "/newUser", method = RequestMethod.POST)
  public String newUserPost(
    HttpServletRequest request,
    @ModelAttribute("email") String userEmail,
    @ModelAttribute("username") String username,
    Model model
  ) throws Exception {
    model.addAttribute("classActiveNewAccount", true);
    model.addAttribute("email", userEmail);
    model.addAttribute("username", username);

    if (userService.findByUsername(username) != null) {
      model.addAttribute("usernameExists", true);

      return "index";
    }

    if (userService.findByEmail(userEmail) != null) {
      model.addAttribute("emailExists", true);

      return "index";
    }

    User user = new User();
    user.setUsername(username);;
    user.setEmail(userEmail);

    String password = SecurityUtility.randomPassword();

    String encryptedPassword = SecurityUtility.passwordEncoder().encode(password);
    user.setPassword(encryptedPassword);

    Role role = new Role();
    role.setRoleId(1);
    role.setName("ROLE_USER");
    Set < UserRole > userRoles = new HashSet < > ();
    userRoles.add(new UserRole(user, role));
    userService.createUser(user, userRoles);

    String token = UUID.randomUUID().toString();
    userService.createPasswordResetTokenForUser(user, token);

    String appUrl = "http://" + request.getServerName() + ":" + request.getServerPort() + request.getContextPath();

    SimpleMailMessage email = mailConstructor.constructResetTokenEmail(appUrl, request.getLocale(), token, user, password);

    mailSender.send(email);

    model.addAttribute("emailSent", "true");

    return "myAccount";
  }

  @RequestMapping("/newUser")
  public String newUser(
    Locale locale,
    @RequestParam("token") String token,
    Model model) {

    PasswordResetToken passToken = userService.getPasswordResetToken(token);

    if (passToken == null) {
      String message = "Invalid Token.";
      model.addAttribute("message", message);
      return "redirect:/badRequest";
    }

    User user = passToken.getUser();
    String username = user.getUsername();

    UserDetails userDetails = userSecurityService.loadUserByUsername(username);

    Authentication authentication = new UsernamePasswordAuthenticationToken(userDetails, userDetails.getPassword(), userDetails.getAuthorities());

    SecurityContextHolder.getContext().setAuthentication(authentication);

    model.addAttribute("user", user);

    model.addAttribute("classActiveEdit", true);
    return "myProfile"; //possibly change to index page
  }
}

我在我的 Application.java 文件中有这个来创建一个用于测试目的的用户。 

@Override
public void run(String...args) throws Exception {
  User user1 = new User();
  user1.setFirstName("Kyle");
  user1.setLastName("Drew");
  user1.setUsername("kd");
  user1.setPassword(SecurityUtility.passwordEncoder().encode("p"));
  user1.setEmail("kd@me.com");
  Set < UserRole > userRoles = new HashSet < > ();
  Role role1 = new Role();
  role1.setRoleId(1);
  role1.setName("ROLE_USER");
  userRoles.add(new UserRole(user1, role1));

  userService.createUser(user1, userRoles);
}

这是调试后的变量图。

【问题讨论】：

  • 它是空的，所以它不能渲染它。创建一个条件，如果它为空，则将用户名设为一些占位符文本
  • 模板上下文中没有名为user 的变量。发布负责此页面的 Spring MVC 控制器方法。
  • 添加了家庭控制器
  • 看起来您添加到模型中的user 对象是null，因此当您尝试渲染user.username 时，您会遇到第一个错误。尝试在调试器中单步执行您的控制器，以查看 user 的值是什么。
  • 当我启动服务器并连接到mysql中的数据库时，我得到确认User kd already Exists. Nothing will be done.

标签： java spring thymeleaf


【解决方案1】：

我发现了这个问题。在 SecurityConfig.Java 文件中，我没有 .loginPage 指向创建异常的正确位置。

http
  .csrf().disable().cors().disable()
  .formLogin().failureUrl("/login?error").defaultSuccessUrl("/")
  .loginPage("/login").permitAll()
  .and()
  .logout().logoutRequestMatcher(new AntPathRequestMatcher("/logout"))
  .logoutSuccessUrl("/?logout").deleteCookies("remember-me").permitAll()
  .and()
  .rememberMe();
}

【讨论】：

    【解决方案2】：

    您可以通过检查user 是否为空来避免此异常。

    <span style="font-style: italic;" th:text="${user != null} ? ${#strings.toUpperCase(user.username)} : 'user is null'"></span>

    但是，更好的方法是确保 user 在未初始化的情况下不会被添加到模型中。

    【讨论】：

    • 我创建的令牌可以很好地访问个人资料页面，并且当我使用令牌时，用户名会显示在它应该出现的位置。但是当我尝试使用凭据登录时。我得到了异常Property or field 'id' cannot be found on null。我会问教练，但如果在 udemy 上没有他回应的问题页面有任何迹象，他显然不会回答问题。
    • 仍然出现异常。我做了一个调试器并添加了到达断点时得到的变量。
    【解决方案3】：

    在放入模型之前确保您的用户对象不为空

    【讨论】：

    • 根据我提供的信息向我解释您看到的东西 = null 的位置。唯一应该是 = null 是如果他们的用户名或电子邮件已经存在。
    • 应该是null，而您的错误消息field username cannot be found *on null* 则表明并非如此。您可以在调试器中轻松解决它。
    • 这很好，但我不确定我在看什么。在寻找关于我应该寻找什么的好文档方面有任何帮助吗？正如我所说，我是这门语言的新手，讲师像 youtube 教程一样教授课程（即不解释任何内容，他解释的内容非常模糊，以至于它所做的只是导致挫败感）。
    • 在控制器中将用户添加到模型中的任何位置放置一个断点，例如。 model.addAttribute("user", user);。检查user的值，看是否为null。
    • 好吧，我在 Eclipse 中添加了断点，它指出我在守护线程中的 throw new SpelEvaluationException(SpelMessage.PROPERTY_OR_FIELD_NOT_READABLE_ON_NULL, name); 最后一项是 owns: NioEndpoint$NioSocketWrapper (id=122) 不管这意味着什么
    猜你喜欢
    • 2018-08-07
    • 2016-11-16
    • 1970-01-01
    • 2018-05-04
    • 2018-01-09
    • 2019-04-27
    • 2020-01-21
    • 2021-08-22
    • 1970-01-01
    相关资源
    最近更新 更多
    热门标签
    Java Python linux javascript Mysql C# Docker 算法 前端 SpringBoot Redis Vue spring 设计模式 .net core .net kubernetes c++ 数据库 数据结构 大数据 js 机器学习 微服务 Android Go 程序员 面试 JVM ASP.net core 云原生 人工智能 后端 PHP git CSS golang k8s Nginx Django mybatis 深度学习 多线程 React 架构 devops 爬虫 云计算 Spring Boot LeetCode