In Spring Boot, the @ConfigurationProperties annotation is used to bind properties defined in the application properties file to a POJO (Plain Old Java Object). This allows you to map properties to fields in your Java class, providing a convenient way to access and manage configuration settings. The other annotations serve different purposes in Spring Boot, but @ConfigurationProperties is specifically designed for property binding.

Spring Cloud and Eureka work together for service discovery by adding the @EnableDiscoveryClient annotation to the Spring Boot application class. This annotation enables the application to register itself with the Eureka server and discover other services.

In Spring Boot, the "@Primary" annotation is used to designate a specific bean as the primary candidate for autowiring when there are multiple candidates for the same type. This is particularly useful when you have multiple beans of the same type, and you want to specify which one should be injected by default. The other options are related to autowiring but do not serve this specific purpose.

To customize the response body of a Spring Boot controller method, the @ResponseBody annotation is used. This annotation tells Spring that the return value of the method should be bound to the web response body, allowing you to customize the content that is sent back to the client. It's a key annotation for building RESTful web services with Spring Boot.

You can handle exceptions at the @RestController level by using @ExceptionHandler methods within the controller itself. This approach is different from using @ControllerAdvice, which is used for global exception handling across the application. @ControllerAdvice allows you to define exception handling methods that can be reused across multiple controllers, while @ExceptionHandler within the controller is specific to that controller.

To enable a service to register itself with Eureka Server in Spring Cloud, you can annotate the service class with @EnableDiscoveryClient. This annotation allows the service to participate in service discovery.

To resolve ambiguity in autowiring of beans, you can use the @Qualifier annotation to specify the bean name or qualifier explicitly. This approach ensures that the correct bean is injected. The @Primary annotation designates a primary bean, which can also help resolve ambiguity. The other options don't directly address ambiguity resolution.

Option 3 is the recommended approach. Tools like WireMock and MockServer allow you to create mock endpoints for external APIs, ensuring that actual API calls are not made during testing.

In Spring Security, the AuthenticationProvider is responsible for creating a user Authentication object from an HttpServletRequest. The AuthenticationProvider is a core component in Spring Security that takes care of authenticating users. It verifies user credentials and loads user-specific details, ultimately creating the Authentication object that represents the authenticated user.

In Spring Boot, you can use the ${env} placeholder in the application properties file to resolve property values from environment variables. This is useful for configuring your Spring Boot application dynamically based on the environment it runs in, such as setting database connection parameters or API keys from environment variables.