Spring Boot中如何解决‘非空属性引用空值或瞬态值’异常

我是一名Spring Boot初学者，目前处于学习阶段。我开发了一个创建员工并将信息保存到数据库的API，运行时遇到异常，谷歌搜索后没能找到解决方案，恳请帮忙解决。

EmployeeController类 #

package net.javaguides.springboot.controller;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import net.javaguides.springboot.model.Employee;
import net.javaguides.springboot.service.EmployeeService;

@RestController
@RequestMapping("/api/employees")
public class EmployeeController {
    
    private EmployeeService employeeService;

    public EmployeeController(EmployeeService employeeService) {
        super();
        this.employeeService = employeeService;
    }
    
    // 构建创建员工的Rest API
    
    @PostMapping
    public ResponseEntity<Employee> saveEmployee(@RequestBody Employee employee) {
        return new ResponseEntity<Employee>(employeeService.saveEmployee(employee), HttpStatus.CREATED);
    }

}

Employee实体类 #

package net.javaguides.springboot.model;

import jakarta.persistence.Column;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import jakarta.persistence.Table;
import lombok.Data;

@Data
@Entity
@Table(name="employee")
public class Employee {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    
    @Column(name="first_name",nullable=false)
    private String firstName;
    
    @Column(name="last_name")
    private String lastName;
    
    @Column(name="email")
    private String email;
}

EmployeeRepository接口 #

package net.javaguides.springboot.repository;

import org.springframework.data.jpa.repository.JpaRepository;

import net.javaguides.springboot.model.Employee;

public interface EmployeeRepository extends JpaRepository<Employee, Long >{

}

EmployeeService接口 #

package net.javaguides.springboot.service;

import net.javaguides.springboot.model.Employee;

public interface EmployeeService {

    Employee saveEmployee(Employee employee);
}

EmployeeServiceImpl实现类 #

package net.javaguides.springboot.service.impl;

import org.springframework.stereotype.Service;

import net.javaguides.springboot.model.Employee;
import net.javaguides.springboot.repository.EmployeeRepository;
import net.javaguides.springboot.service.EmployeeService;

@Service
public class EmployeeServiceImpl implements EmployeeService{
    
    private EmployeeRepository employeeRepository;
    
    // 强制参数场景下使用构造方法注入
    public EmployeeServiceImpl(EmployeeRepository employeeRepository) {
        super();
        this.employeeRepository = employeeRepository;
    }
    

    @Override
    public Employee saveEmployee(Employee employee) {
        
        return employeeRepository.save(employee);
    }

}

项目结构 #

数据库表结构（employee表） #

内容的提问来源于stack exchange，提问作者Indresh Kumar