当我一起使用@Bean和@Component注释时会发生什么?

Question

我正在尝试配置我的spring安全应用程序。

我想创建我自己的UserDetailsService.

我这样做:

public class ApplicationUserService implements UserDetailsService {
@Override
public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
return this.someUser();
}
}

我有两种方法来添加这个UserService到Spring Security

1. 添加到配置类中。像这样:

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
@Bean
@Override
protected UserDetailsService userDetailsService() {
return applicationUserService;
}
}

2. 或者在我的类上添加@Component或@Service的注释。当我只选择1种方式时，一切都很好，但我有一个问题:为什么当我试图使用这两种变体(添加@Service和添加@Bean配置)没有任何工作?我没有得到异常，错误或类似的东西在控制台:

2021-09-11 17:26:16.755  INFO 15819 --- [           main] com.example.test.TestApplication         : Starting TestApplication using Java 16.0.2 on aleksander-MS-7A71 with PID 15819 (/home/aleksander/programming/java/4fun/test/target/classes started by aleksander in /home/aleksander/programming/java/4fun/test)
2021-09-11 17:26:16.756  INFO 15819 --- [           main] com.example.test.TestApplication         : No active profile set, falling back to default profiles: default
2021-09-11 17:26:17.402  INFO 15819 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2021-09-11 17:26:17.409  INFO 15819 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2021-09-11 17:26:17.409  INFO 15819 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.52]
2021-09-11 17:26:17.442  INFO 15819 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2021-09-11 17:26:17.442  INFO 15819 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 630 ms
2021-09-11 17:26:17.555  INFO 15819 --- [           main] o.s.s.web.DefaultSecurityFilterChain     : Will secure any request with [org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter@6981f8f3, org.springframework.security.web.context.SecurityContextPersistenceFilter@38bb9d7a, org.springframework.security.web.header.HeaderWriterFilter@62db3891, org.springframework.security.web.authentication.logout.LogoutFilter@48528634, org.springframework.security.web.authentication.www.BasicAuthenticationFilter@80bfdc6, org.springframework.security.web.savedrequest.RequestCacheAwareFilter@78d6447a, org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter@5e65afb6, org.springframework.security.web.authentication.AnonymousAuthenticationFilter@623dcf2a, org.springframework.security.web.session.SessionManagementFilter@2819c460, org.springframework.security.web.access.ExceptionTranslationFilter@6f49d153, org.springframework.security.web.access.intercept.FilterSecurityInterceptor@60bbacfc]
2021-09-11 17:26:17.676  INFO 15819 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2021-09-11 17:26:17.682  INFO 15819 --- [           main] com.example.test.TestApplication         : Started TestApplication in 1.215 seconds (JVM running for 1.794)

Answer 1

按照您描述问题的方式，除非您定义了bean首选项，否则应用程序肯定会抛出异常。

第一个例子:基本上，UserDetailsService是一个interface，您通过将bean声明为

来提供它的实现

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
@Bean
@Override
protected UserDetailsService userDetailsService() {
return new ApplicationUserService();
}
}

第二个案例:您希望通过使用@Service或@Component注释声明另一个bean来检查行为，如下所示

@Service
public class ApplicationUserService implements UserDetailsService {  
@Override
public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
return new UserDetails();
}
}

如果你试图同时使用上述情况，它将不起作用。这种情况非常简单，您向spring容器提供了两个类型为UserDetailsService的bean，因此它将无法确定应该使用哪一个。

如果你想检查两种情况下的行为，你必须为bean设置优先级，所以在这种情况下，你可以用@Primary注释标记其中一个bean。

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
@Primary
@Bean
@Override
protected UserDetailsService userDetailsService() {
return new ApplicationUserService();
}
}