In a scenario where there are multiple beans of the same type, how can one specify which bean should be Autowired?
- Use the @Qualifier annotation with the desired bean's name.
- Use the @Autowired annotation with the desired bean's variable name.
- Use the @Inject annotation with the desired bean's ID.
- Use the @Resource annotation with the desired bean's name.
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 _____ annotation used to indicate service components.
- @Bean
- @Component
- @Controller
- @Repository
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.
Which annotation is used to define a bean in the Spring context?
- @Bean
- @Component
- @Inject
- @Service
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.
The error messages of validation constraints in Spring Boot can be externalized using the _____ property in the constraint annotation.
- @ErrorMessage
- @Message
- @MessageCode
- @MessageSource
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.
How can you implement Token Enhancement to include additional information in the OAuth2 access token?
- Implement a custom token enhancer that extends DefaultTokenServices.
- Include the additional information in the request body when requesting a token.
- Configure the OAuth2 Authorization Server with the new information.
- Extend the OAuth2 access token expiration time.
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, the _____ annotation can be used on a method within a @Controller or @RestController in Spring Boot.
- @ExceptionHandler
- @RequestMapping
- @ResponseBody
- @ResponseStatus
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.
Suppose you are developing a large enterprise application using Spring. How would you optimize the bean lifecycle to ensure minimal resource utilization and maximum performance?
- Implement the SmartInitializingSingleton interface to defer time-consuming initialization tasks until all singletons are created.
- Use the @Lazy annotation on beans to load them lazily only when they are first accessed.
- Set the destroy-method attribute in the bean configuration to release resources explicitly during bean destruction.
- Use the @DependsOn annotation to define bean dependencies explicitly to control their initialization order.
To optimize the bean lifecycle in a large enterprise application, implementing the SmartInitializingSingleton interface allows you to defer time-consuming initialization tasks until all singletons are created, minimizing resource utilization during startup. The other options may help in specific cases but don't address the overall lifecycle optimization.
You are developing a Spring Boot application where a bean is required to perform a task immediately after the ApplicationContext has been started. How would you implement this?
- Implement a custom event listener that listens for the ContextRefreshedEvent and executes the task.
- Use the @EventListener annotation on a method and specify the event type as ApplicationStartedEvent.
- Use the @OnStartup annotation on the bean's method.
- Use the @PostConstruct annotation on the bean's method that needs to run after startup.
To execute a task immediately after the ApplicationContext has been started in a Spring Boot application, you can implement a custom event listener that listens for the ContextRefreshedEvent. This event is raised when the ApplicationContext is fully initialized and ready to use. You can then execute your task in response to this event.
How can you profile a production Spring Boot application without affecting its performance significantly?
- Using production profiling tools like VisualVM or Java Flight Recorder.
- Temporarily disabling all logging in the application.
- Increasing the application's memory allocation.
- Running load tests concurrently with the profiling process.
Option 1 is correct. Profiling production Spring Boot applications can be done using tools like VisualVM or Java Flight Recorder without significant performance impact. These tools provide insights into application behavior and resource usage. Disabling all logging (Option 2) is not a recommended approach as logging is essential for debugging and monitoring. Increasing memory allocation (Option 3) may not help with profiling. Running load tests concurrently (Option 4) can further impact performance and is not ideal for profiling.
You are tasked with creating a custom Auto Configuration that provides a set of beans only if a specific library is on the classpath. How would you approach this requirement?
- Create the beans unconditionally, and Spring Boot will automatically handle the classpath check.
- Include the library's JAR file directly in the project to guarantee its presence and enable the beans.
- Use the @ConditionalOnClass annotation on the custom Auto Configuration class and specify the library's class in the annotation's value attribute. This ensures that the beans are created only if the specified class is on the classpath.
- Use the @ConditionalOnProperty annotation with a condition that checks for the presence of the library's JAR file.
To create a custom Auto Configuration that provides beans conditionally based on the presence of a specific library on the classpath, you should use the @ConditionalOnClass annotation. Specify the library's class in the annotation's value attribute. This approach ensures that the beans are only created when the specified class is available on the classpath, ensuring the required conditions are met.