Spring Security项目报错：需在配置中定义UserService类型Bean

报错信息：

Consider defining a bean of type 'de.JBR.mongo.models.UserService' in your configuration.

我的Spring Boot启动类代码 #

@ComponentScan({ "de.JBR.mongo.repositry", "de.JBR.mongo.api.models", "security.config", "security"})
@EnableMongoRepositories("de.JBR.mongo")
@SpringBootApplication
@AllArgsConstructor 
public class EssensManagerApplication {

    private final UserRepositry repositry;
    
    public static void main(String[] args) {
        SpringApplication.run(EssensManagerApplication.class, args);
    }
}

UserService类代码（de.JBR.mongo.models.UserService） #

@AllArgsConstructor
@Service
public class UserService implements UserDetailsService{

    private final static String USER_NOT_FOUND = "Nutzer mit Name %s nicht gefunden";
    private final UserRepositry repositry;
    
    @Override
    @Bean
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
    
        return repositry.findByUsername(username)
                .orElseThrow(() -> new UsernameNotFoundException(String.format(USER_NOT_FOUND, username)));
    }

}

问题原因 #

1. UserService所在的de.JBR.mongo.models包不在启动类@ComponentScan的扫描范围内，Spring无法识别带有@Service注解的该类，无法将其注册为容器Bean。
2. loadUserByUsername方法上错误添加了@Bean注解，该注解用于定义Bean的生成方法，而此处是实现UserDetailsService的接口方法，属于业务逻辑实现，不需要该注解。

解决方案 #

1. 修正组件扫描范围 #

将de.JBR.mongo.models加入@ComponentScan的扫描路径，修改后的启动类注解：

@ComponentScan({ "de.JBR.mongo.repositry", "de.JBR.mongo.api.models", "de.JBR.mongo.models", "security.config", "security"})

或者更简洁地直接扫描根包，覆盖所有子模块：

@ComponentScan({ "de.JBR", "security"})

另外，@SpringBootApplication本身默认包含组件扫描逻辑，会扫描启动类所在包及其子包。如果启动类位于de.JBR包下，甚至可以直接移除@ComponentScan注解，让Spring自动完成扫描。

2. 移除多余的@Bean注解 #

修改UserService的接口实现方法，去掉不必要的@Bean：

@AllArgsConstructor
@Service
public class UserService implements UserDetailsService{

    private final static String USER_NOT_FOUND = "Nutzer mit Name %s nicht gefunden";
    private final UserRepositry repositry;
    
    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
    
        return repositry.findByUsername(username)
                .orElseThrow(() -> new UsernameNotFoundException(String.format(USER_NOT_FOUND, username)));
    }

}

内容的提问来源于stack exchange，提问作者Jakob Ball