Technology
Solving Multiple Beans Error in Spring UserDetailsService
Solving Multiple Beans Error in Spring UserDetailsService
The error message related to the UserDetailsService interface in a Spring application signifies that the Spring framework has identified multiple beans of the same type and is unable to decide which one to inject into your component. This issue is frequently encountered in scenarios where you have defined multiple implementations of the same interface.
Why It Happens
The primary reason for this error is the presence of multiple implementations of the UserDetailsService interface. Spring will throw this error if it finds more than one class that implements this interface without a clear indication of which one to use. Additionally, the issue can arise due to the process of component scanning, where Spring scans the classpath for component classes annotated with @Service, @Repository, etc., and finds multiple candidates for autowiring.
How to Fix It
Several approaches can be employed to resolve the UserDetailsService bean resolution issue:
Primary Bean
You can mark one of your UserDetailsService implementations as the primary bean using the @Primary annotation. This directs Spring to select this bean when there are multiple candidates.
public class MyPrimaryUserDetailsService implements UserDetailsService {
// Implementation
}
Qualifiers
If you need to use different implementations in different places, you can use the @Qualifier annotation to specify the exact bean to autowire.
public class MyComponent {
private final UserDetailsService userDetailsService;
@Autowired
public MyComponent(@Qualifier("mySpecificUserDetailsService") UserDetailsService userDetailsService) {
userDetailsService;
}
}
Remove Unused Beans
If one of the implementations is not necessary, consider removing it or commenting it out to eliminate the conflict.
Custom Configuration
In more complex configurations, you can create a configuration class where you explicitly define which beans to use.
public class SecurityConfig {
@Bean
public UserDetailsService userDetailsService {
return new MySpecificUserDetailsService();
}
}
Check Component Scanning
Ensure that your component scanning is correctly configured to avoid picking up unintended beans.
Conclusion
By either designating a primary bean, using qualifiers, or adjusting your bean definitions, you can resolve the ambiguity and allow Spring to correctly autowire your UserDetailsService. Choose the method that best fits your application's architecture and requirements.