The @WebMvcTest annotation is used to test the web layer of a Spring Boot application. It focuses on setting up the application context with only the necessary components for testing the web layer, such as controllers and web-related beans.

Leveraging Spring Boot's conditional annotations allows you to enable your custom auto-configuration only when the required conditions are met, ensuring it's efficient and maintainable. The other options may lead to issues or reduced maintainability.

When configuring a CacheManager in Spring Boot, the expireAfterWrite property can be used to set the time-to-live (TTL) values for cache entries. This property determines how long cache entries remain valid before they are considered expired and potentially removed from the cache. It's essential for controlling cache behavior.

When a service registered with Eureka becomes unavailable, you can handle it by implementing a fallback mechanism in the service. Hystrix is a popular choice for this purpose in a Spring Cloud application. It allows you to define a fallback method that will be executed when the primary service is unavailable. This ensures graceful degradation of service and improves system resilience. Configuring Eureka to retry registering the service or using its circuit breaker mechanism is not the primary approach for handling unavailability.

Ribbon is used in a Spring Cloud microservices architecture for load balancing. It distributes incoming requests across multiple instances of a service, improving system reliability and performance.

To customize access-denied behavior, you should implement a custom AccessDeniedHandler, which allows you to define how to handle access-denied situations. You then register this handler with Spring Security to apply it to secured methods.

To optimize the performance of Spring Data JPA when dealing with large datasets, using PagingAndSortingRepository is recommended to read the datasets in chunks. This repository interface extends CrudRepository and provides methods for pagination and sorting, making it suitable for efficiently fetching and processing large datasets by breaking them into manageable chunks.

The primary responsibility of an OAuth2 Authorization Server in a Spring Boot application is to authenticate users and grant access tokens to authorized clients. It does not store user passwords but rather validates user credentials and authorizes access to protected resources. It also does not manage user profiles and preferences, nor does it control database access; these are typically the tasks of the application's authentication system and database itself.

The primary role of the UserDetailsService in Spring Security is to load user details (including username, password, and roles) from a data store, typically a database. It's a fundamental component used for authentication and authorization, as it provides the necessary user information for the security framework to make access control decisions. The other options describe tasks related to authentication and authorization but are not the primary role of UserDetailsService.

The correct annotation to handle exceptions globally across the entire Spring Boot application is @ControllerAdvice. This annotation allows you to define global exception handlers that can be applied to multiple controllers. It's a powerful tool for managing exceptions consistently throughout your application. The other options are not used for this purpose.

Spring Boot provides the MockMvc class, which allows you to simulate HTTP requests and responses for testing controller methods without the need to start a server. It's a crucial tool for integration testing in Spring Boot.

In Spring Boot, you can conditionally enable caching by using the @ConditionalOnProperty annotation with the property name as "spring.cache.enabled." This annotation allows caching to be enabled only when the specified property is set to true. The other annotations do not provide conditional caching based on a property.