The @Repository annotation in Spring Boot is used specifically for data access operations. It is a specialization of @Component and is used to indicate that the class defines a data repository. @Component, on the other hand, is a more general-purpose annotation for defining Spring beans. @Repository is used to simplify data access configuration and exception translation.

In Spring Boot, the @Validated annotation is used along with specific constraint annotations like @NotBlank, @Min, @Max, etc., to apply validation constraints on a field. The @Validated annotation indicates that the validation should be performed on the annotated field or method parameter. It is a fundamental part of Spring Boot's validation framework.

To conditionally apply caching logic in Spring Boot, developers use the @Cacheable annotation. This annotation allows them to specify conditions under which the caching logic should be applied, typically by providing a SpEL (Spring Expression Language) expression. It's a powerful tool for selectively caching method results.

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.