When there are multiple beans of the same type, you can specify which bean should be autowired using the @Qualifier annotation with the desired bean's name. This helps Spring resolve the ambiguity. The other options, while related to dependency injection, do not directly address the issue of selecting a specific bean from multiple candidates.

The @Service annotation in Spring Boot is a specialized form of the @Component annotation used to indicate service components. It is used to define a class as a service in the Spring application context. While @Repository is used for DAOs, @Controller is used for controllers, and @Bean is a more generic annotation for creating managed beans. The @Service annotation provides additional semantic meaning to the class.

The @Bean annotation is used to define a bean in the Spring context. When you annotate a method with @Bean, it tells Spring that the method should be used to create and configure a bean. This is commonly used for defining custom beans in Java-based Spring configurations. The other annotations (@Inject, @Component, and @Service) have different purposes and are not used for defining beans in the same way as @Bean.

To externalize error messages for validation constraints in Spring Boot, you can use the message property in the constraint annotation, and then reference externalized messages using a message source, often defined in a properties file or through Spring's message source mechanisms. This approach makes it easier to manage and internationalize error messages.

To include additional information in the OAuth2 access token, you can implement a custom token enhancer by extending DefaultTokenServices. This allows you to manipulate the token content and add the desired information. The other options are not typically used for token enhancement.

The @Primary annotation in Spring is used to give a preference to a bean when multiple beans of the same type exist. It tells Spring which bean should be considered as the primary candidate for autowiring when there are multiple candidates of the same type. The other options, such as @Qualifier, @PreferencedBean, and @Priority, do not serve the same purpose as @Primary.

The @Repository annotation in Spring is used to mark a class as a repository, especially in the context of Spring Data JPA. It helps in automatic generation of database queries based on method names. It does not generate exceptions or specify the database schema. Its primary role is to enable Spring to manage database operations and perform exception translation when necessary. It is not related to creating RESTful web services.

To handle exceptions locally within a controller in Spring Boot, you can use the @ExceptionHandler annotation on a method within a @Controller or @RestController. This annotation allows you to define methods that will handle specific exceptions thrown by the controller's methods.

Option 1 is correct. Profiling production Spring Boot applications can be done using tools like VisualVM or Java Flight Recorder without significant performance impact. These tools provide insights into application behavior and resource usage. Disabling all logging (Option 2) is not a recommended approach as logging is essential for debugging and monitoring. Increasing memory allocation (Option 3) may not help with profiling. Running load tests concurrently (Option 4) can further impact performance and is not ideal for profiling.

To create a custom Auto Configuration that provides beans conditionally based on the presence of a specific library on the classpath, you should use the @ConditionalOnClass annotation. Specify the library's class in the annotation's value attribute. This approach ensures that the beans are only created when the specified class is available on the classpath, ensuring the required conditions are met.