Spring Boot银行应用注册时出现Entity must not be null错误求助

我正在开发一个基于Spring Boot、Hibernate、MySQL的银行Web应用，启动应用访问http://localhost:8080/并填写完注册表单提交后，IntelliJ中出现报错，表单提交失败。

报错信息 #

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.dao.InvalidDataAccessApiUsageException: Entity must not be null.; nested exception is java.lang.IllegalArgumentException: Entity must not be null.
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)
    ...（省略中间栈信息）
Caused by: java.lang.IllegalArgumentException: Entity must not be null.
    at org.springframework.util.Assert.notNull(Assert.java:201)
    ...（省略中间栈信息）

application.properties配置 #

数据库已创建且配置完成，连接正常。

UserController代码 #

package com.userfront.controller;

import java.security.Principal;

import org.springframework.beans.factory.annotation.Autowired;
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 com.userfront.domain.User;
import com.userfront.service.UserService;

@Controller
@RequestMapping("/user")
public class UserController {

    @Autowired
    private UserService userService;

    @RequestMapping(value = "/profile", method = RequestMethod.GET)
    public String profile(Principal principal, Model model) {
        User user = userService.findByUsername(principal.getName());

        model.addAttribute("user", user);

        return "profile";
    }

    @RequestMapping(value = "/profile", method = RequestMethod.POST)
    public String profilePost(@ModelAttribute("user") User newUser, Model model) {
        User user = userService.findByUsername(newUser.getUsername());
        user.setUsername(newUser.getUsername());
        user.setFirstName(newUser.getFirstName());
        user.setLastName(newUser.getLastName());
        user.setEmail(newUser.getEmail());
        user.setPhone(newUser.getPhone());

        model.addAttribute("user", user);

        userService.saveUser(user);

        return "profile";
    }

}

RequestFilter代码 #

package com.userfront.config;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;

@Component
@Order(Ordered.HIGHEST_PRECEDENCE)
public class RequestFilter implements Filter {

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) {
        HttpServletResponse response = (HttpServletResponse) res;
        HttpServletRequest request = (HttpServletRequest) req;

        response.setHeader("Access-Control-Allow-Origin", "http://localhost:4200");
        response.setHeader("Access-Control-Allow-Methods", "POST, PUT, GET, OPTIONS, DELETE");
        response.setHeader("Access-Control-Allow-Headers", "x-requested-with");
        response.setHeader("Access-Control-Max-Age", "3600");
        response.setHeader("Access-Control-Allow-Credentials", "true");

        if (!(request.getMethod().equalsIgnoreCase("OPTIONS"))) {
            try {
                chain.doFilter(req, res);
            } catch(Exception e) {
                e.printStackTrace();
            }
        } else {
            System.out.println("Pre-flight");
            response.setHeader("Access-Control-Allow-Methods", "POST,GET,DELETE");
            response.setHeader("Access-Control-Max-Age", "3600");
            response.setHeader("Access-Control-Allow-Headers", "authorization, content-type," +
                    "access-control-request-headers,access-control-request-method,accept,origin,authorization,x-requested-with");
            response.setStatus(HttpServletResponse.SC_OK);
        }

    }

    public void init(FilterConfig filterConfig) {}

    public void destroy() {}

}

问题分析与解决方案 #

核心问题 #

注册表单的请求被错误发送到了/user/profile接口——这个接口是用户信息更新逻辑，而非注册逻辑：

1. 注册时新用户名在数据库中不存在，userService.findByUsername(newUser.getUsername())返回null
2. 后续对null对象调用setXXX方法会触发空指针，最终调用userService.saveUser(user)时传入null，触发Entity must not be null报错

修复步骤 #

1. 新增注册专用接口
   在UserController中添加注册POST接口，直接处理新用户保存：

   @RequestMapping(value = "/register", method = RequestMethod.POST)
   public String registerPost(@ModelAttribute("user") User newUser, Model model) {
       // 先校验用户名是否已存在
       if (userService.findByUsername(newUser.getUsername()) != null) {
           model.addAttribute("error", "用户名已存在，请更换");
           return "register"; // 返回注册页面提示错误
       }
       userService.saveUser(newUser);
       return "redirect:/login"; // 注册成功后跳转到登录页
   }
   

2. 调整注册表单提交路径
   修改注册页面的form标签，将action属性设置为/user/register，确保请求发送到正确的接口。

3. 检查UserService的save逻辑
   确认userService.saveUser()方法能正确处理新用户的保存（比如使用JPA的save()方法，会自动区分新增和更新），避免仅支持更新的逻辑。

4. 优化跨域配置（可选）
   若注册页面是Spring Boot自带的模板（如Thymeleaf），当前跨域配置允许的是http://localhost:4200，可能和应用实际运行的8080端口冲突，可以调整为：

   response.setHeader("Access-Control-Allow-Origin", "http://localhost:8080");
   

   或者移除跨域Filter（如果不需要前后端分离跨域）。

内容的提问来源于stack exchange，提问作者bilal sajai