Spring Boot执行CommandLineRunner失败问题求助

Spring Boot项目执行CommandLineRunner时抛出Failed to execute CommandLineRunner异常，控制台错误日志如下：

java.lang.IllegalStateException: Failed to execute CommandLineRunner
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:774) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:755) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-2.7.4.jar:2.7.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295) ~[spring-boot-2.7.4.jar:2.7.4]
at io.getarrays.userservice.UserserviceApplication.main(UserserviceApplication.java:19) ~[classes/:na]
Caused by: java.lang.NullPointerException: Cannot invoke "io.getarrays.userservice.domain.User.getRoles()" because "user" is null
at io.getarrays.userservice.service.UserServiceImpl.addRoleToUser(UserServiceImpl.java:36) ~[classes/:na]
at io.getarrays.userservice.service.UserServiceImpl$$FastClassBySpringCGLIB$$cf86a147.invoke(<generated>) ~[classes/:na]
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) ~[spring-core-5.3.23.jar:5.3.23]
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:793) ~[spring-aop-5.3.23.jar:5.3.23]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.3.23.jar:5.3.23]
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763) ~[spring-aop-5.3.23.jar:5.3.23]
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:123) ~[spring-tx-5.3.23.jar:5.3.23]
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:388) ~[spring-tx-5.3.23.jar:5.3.23]
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:119) ~[spring-tx-5.3.23.jar:5.3.23]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.23.jar:5.3.23]
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763) ~[spring-aop-5.3.23.jar:5.3.23]
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:708) ~[spring-aop-5.3.23.jar:5.3.23]
at io.getarrays.userservice.service.UserServiceImpl$$EnhancerBySpringCGLIB$$4c838cf9.addRoleToUser(<generated>) ~[classes/:na]
at io.getarrays.userservice.UserserviceApplication.lambda$run$0(UserserviceApplication.java:35) ~[classes/:na]
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:771) ~[spring-boot-2.7.4.jar:2.7.4]
... 5 common frames omitted

相关代码：

@SpringBootApplication
public class UserserviceApplication {

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

    @Bean
    CommandLineRunner run(UserService userService){
        return args -> {
            // Save Role
            userService.saveRole(new Role(null, "ROLE_USER"));
            userService.saveRole(new Role(null, "ROLE_MANAGER"));
            userService.saveRole(new Role(null, "ROLE_ADMIN"));
            userService.saveRole(new Role(null, "ROLE_SUPER_ADMIN"));

            // Save User
            userService.saveUser(new User(null,"John Travolta","jhon","1234", new ArrayList<>()));
            userService.saveUser(new User(null,"Will Smith","will","1234", new ArrayList<>()));
            userService.saveUser(new User(null,"Jim Carry","jim","1234", new ArrayList<>()));
            userService.saveUser(new User(null,"Arnold Schwarzenegger","arnold","1234", new ArrayList<>()));

            // Add role to user
            userService.addRoleToUser("john","ROLE_USER");
            userService.addRoleToUser("will","ROLE_MANAGER");
            userService.addRoleToUser("jim","ROLE_ADMIN");
            userService.addRoleToUser("arnold","ROLE_SUPER_ADMIN");
            userService.addRoleToUser("arnold","ROLE_ADMIN");
            userService.addRoleToUser("arnold","ROLE_USER");
        };

    }

}

问题分析 #

核心异常为java.lang.NullPointerException: Cannot invoke "io.getarrays.userservice.domain.User.getRoles()" because "user" is null，本质原因是：

• 保存第一个用户时，用户名写为jhon
• 后续添加角色时，使用的用户名是john
• 拼写不一致导致userService.addRoleToUser方法查询不到用户，返回null，调用user.getRoles()时触发空指针。

解决方案 #

1. 修正用户名拼写错误 #

将保存用户的代码中，第一个用户的用户名从jhon改为john，保持与添加角色时一致：

userService.saveUser(new User(null,"John Travolta","john","1234", new ArrayList<>()));

2. 增强服务层空指针防护 #

在UserServiceImpl的addRoleToUser方法中增加空判断，提前抛出明确异常，避免空指针：

public void addRoleToUser(String username, String roleName) {
    User user = userRepository.findByUsername(username);
    if (user == null) {
        throw new RuntimeException("用户不存在：" + username);
    }
    Role role = roleRepository.findByName(roleName);
    if (role == null) {
        throw new RuntimeException("角色不存在：" + roleName);
    }
    user.getRoles().add(role);
    userRepository.save(user);
}

内容的提问来源于stack exchange，提问作者Angello G_De la torre