运行Spring Boot应用时遭遇异常，请求协助排查解决

异常信息 #

第一个异常 #

java.lang.IllegalStateException: Failed to execute CommandLineRunner
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:771) ~[spring-boot-2.7.12.jar:2.7.12]
at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:752) ~[spring-boot-2.7.12.jar:2.7.12]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:314) ~[spring-boot-2.7.12.jar:2.7.12]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1303) ~[spring-boot-2.7.12.jar:2.7.12]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1292) ~[spring-boot-2.7.12.jar:2.7.12]
at project.art_area.ArtAreaApplication.main(ArtAreaApplication.java:19) ~[classes/:na]

第二个异常（根源） #

Caused by: java.lang.NullPointerException: Cannot invoke "art_area.service.LoginServiceImpl.addCustomer(art_area.model.LoginDTO)" because "this.loginService" is null
at art_area.api.LoginApi.addCustomer1(LoginApi.java:22) ~[classes/:na]
at project.art_area.ArtAreaApplication.addCustomer(ArtAreaApplication.java:38) ~[classes/:na]
at project.art_area.ArtAreaApplication.run(ArtAreaApplication.java:26) ~[classes/:na]
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:768) ~[spring-boot-2.7.12.jar:2.7.12]
... 5 common frames omitted

相关代码 #

主类 #

package project.art_area;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import art_area.api.LoginApi;
import art_area.model.LoginDTO;

@SpringBootApplication
public class ArtAreaApplication implements CommandLineRunner{
    
    public static void main(String[] args) {
        SpringApplication.run(ArtAreaApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
        addCustomer();
    }
    
    public void addCustomer()
    {
        LoginApi loginApi=new LoginApi();
        LoginDTO loginDTO=new LoginDTO();
        loginDTO.setFirstname("A");
        loginDTO.setLastname("B");
        loginDTO.setPhonenumber("1234567890");
        loginDTO.setDoctorname("A");
        loginDTO.setSex("M");
        String s=loginApi.addCustomer1(loginDTO);
        System.out.println(s);
    }
}

API类 #

package art_area.api;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import art_area.model.LoginDTO;
import art_area.service.LoginServiceImpl;

@RestController
@RequestMapping(value="/login")
public class LoginApi {
    
    @Autowired
    private LoginServiceImpl loginService;
    
    @PostMapping(value = "/customer")
    public String addCustomer1(LoginDTO loginDTO)
    {
        if(loginService.addCustomer(loginDTO));
        {
            return "customer Successfully added";
        }
        //return "customer already exists";
    }
}

服务类 #

package art_area.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import art_area.model.LoginDTO;
import art_area.repository.LoginRepository;
import art_area.service.LoginService;

@Service(value = "loginService")
public class LoginServiceImpl implements LoginService{

    @Autowired
    private LoginRepository loginRepository;
    
    @Override
    public boolean addCustomer(LoginDTO loginDTO) {
        if(loginRepository.addCustomer(loginDTO))
        {
            return true;
        }
        return false;
    }
}

问题原因分析 #

1. 空指针异常根源：主类中通过new LoginApi()手动创建实例，该对象不受Spring容器管理，@Autowired标注的loginService无法被注入，调用方法时触发空指针。
2. 依赖注入不规范：LoginApi直接注入实现类LoginServiceImpl，而非接口LoginService，违反依赖倒置原则，降低代码可维护性。
3. 语法错误：LoginApi的addCustomer1方法中，if语句后多了分号，导致后续代码块不受条件控制，无论操作结果如何都会返回成功提示。

解决方案 #

1. 主类注入Spring管理的LoginApi实例 #

修改主类，通过@Autowired获取容器中的LoginApi对象，不再手动创建：

package project.art_area;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import art_area.api.LoginApi;
import art_area.model.LoginDTO;

@SpringBootApplication
public class ArtAreaApplication implements CommandLineRunner{
    
    @Autowired
    private LoginApi loginApi;

    public static void main(String[] args) {
        SpringApplication.run(ArtAreaApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
        addCustomer();
    }
    
    public void addCustomer()
    {
        LoginDTO loginDTO=new LoginDTO();
        loginDTO.setFirstname("A");
        loginDTO.setLastname("B");
        loginDTO.setPhonenumber("1234567890");
        loginDTO.setDoctorname("A");
        loginDTO.setSex("M");
        String s=loginApi.addCustomer1(loginDTO);
        System.out.println(s);
    }
}

2. 修改LoginApi的依赖注入为接口类型 #

将LoginApi中的依赖改为接口LoginService，遵循依赖倒置原则：

package art_area.api;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import art_area.model.LoginDTO;
import art_area.service.LoginService;

@RestController
@RequestMapping(value="/login")
public class LoginApi {
    
    @Autowired
    private LoginService loginService;
    
    @PostMapping(value = "/customer")
    public String addCustomer1(LoginDTO loginDTO)
    {
        if(loginService.addCustomer(loginDTO))
        {
            return "customer Successfully added";
        }
        return "customer already exists";
    }
}

3. 修复if语句的多余分号 #

删除if(loginService.addCustomer(loginDTO))后的分号，让条件判断生效。

验证修改 #

完成上述调整后，重启Spring Boot应用，CommandLineRunner会正常执行，空指针异常和启动异常将被解决，代码也更符合Spring开发规范。

内容的提问来源于stack exchange，提问作者sreenivas pothuru