In Spring Boot, the @EnableAuthorizationServer annotation is used to enable OAuth2 Authorization Server capabilities. It allows the application to act as an OAuth2 authorization server, handling client registration, token issuance, and other authorization-related tasks.

In Spring Boot reactive programming, the DeferredResult class is used to represent an asynchronous computation result. It allows a controller to start processing a request and return a DeferredResult immediately, deferring the actual result processing to a later time. This is useful for handling long-running or asynchronous tasks in a non-blocking manner.

Option 1 is the most common approach. Mockito is a popular Java mocking framework that allows you to mock external dependencies, isolating the microservice being tested.

In Spring Boot, you can use the @Value annotation to inject the value of a specific property into a field. This annotation allows you to inject property values from your application.properties or application.yml file directly into your Spring components, making it convenient to access configuration properties within your application code.

In Spring Boot, to manually wire a bean, you would use the "getBean()" method of the ApplicationContext. This method allows you to retrieve a bean from the Spring container by its name or class. The other options, such as "registerBean()," "wireBean()," and "fetchBean()," do not represent the correct method used for manual bean retrieval and wiring in Spring Boot.

The @DataJpaTest annotation in Spring Boot is used for testing the persistence layer. It slices the application context and loads only the relevant beans related to data JPA, making it efficient for testing data access operations.

The correct annotation to secure methods in Spring Security is @Secured. This annotation allows you to specify which roles or authorities are required to access a particular method.

In a Spring Boot application, you can map application-specific exceptions to HTTP status codes using the @ResponseStatus annotation in custom exception classes. This allows you to define the specific HTTP status code to return when a particular exception is thrown, providing fine-grained control over error responses. The other options are not standard practices for mapping exceptions to HTTP status codes in Spring Boot.

The /metrics endpoint in Spring Boot Actuator is specifically used for exposing application metrics. This endpoint provides valuable information about your application's performance, such as memory usage, garbage collection statistics, and custom metrics you can define. Monitoring these metrics is crucial for ensuring the health and performance of your Spring Boot application.

The most efficient way to manage transactions in a Spring Boot application utilizing Spring Data JPA is by using the @Transactional annotation on the service layer. This annotation simplifies transaction management and ensures that all methods within the annotated service class are executed within a single transaction. Embedding SQL transactions within repository methods can lead to issues with transaction boundaries. The other options are not best practices for managing transactions in a Spring Boot application.

The most efficient way to manage transactions in a Spring Boot application utilizing Spring Data JPA is by using declarative transaction management with the @Transactional annotation. It simplifies transaction handling and provides better readability and maintainability. The other options may work but are not considered as efficient and convenient as declarative transaction management.

To make a Spring Boot controller handle requests asynchronously for better scalability, you can use the @Async annotation on controller methods. This enables asynchronous processing of requests without blocking the main thread. Configuring a separate thread pool may be necessary for fine-tuning, but it's not the primary way to enable asynchronous handling in a controller. Using a different web framework is not required, as Spring Boot has built-in support for asynchronous operations. @Transactional is used for database transactions and is unrelated to request handling.