To create efficient custom auto-configurations in Spring Boot, it's essential to minimize the use of conditionals, as excessive conditionals can increase complexity and impact startup time negatively. Additionally, you can leverage lazy initialization to defer the creation of beans until they're needed, optimizing startup. Breaking auto-configuration into smaller, modular configurations also helps improve maintainability and startup time. Avoiding unnecessary dependencies is crucial, as adding more dependencies can increase the startup time.

To ensure smooth deployment and execution of a Spring Boot project on a cloud platform, it's advisable to utilize Spring Cloud for cloud-native features and configurations. This includes binding to cloud-native services, using environment-specific configuration files, and leveraging cloud-specific technologies for seamless integration.

The primary goal of performance tuning in a Spring Boot application is to minimize the application's startup time. A faster startup time ensures that the application can be deployed and respond to requests more quickly. This is particularly important in microservices architectures, where rapid scaling and responsiveness are crucial. Performance tuning can involve optimizing database queries, minimizing the use of heavy frameworks, and other techniques to make the application's initialization as efficient as possible.

Constructor injection is preferred over setter injection when you need to inject dependencies that are immutable and required for the object to function properly. This ensures that the object is in a valid state from the moment it is created. Setter injection is more suitable when you want to inject optional or mutable dependencies after the object is constructed. The other options are not accurate reasons for choosing one injection method over the other.

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.

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.