To perform unit testing on the web layer of a Spring Boot application without loading the complete context, you should use the @WebMvcTest annotation. This annotation focuses only on the web layer and is suitable for testing controllers.

In a Spring Boot application, the @Transactional annotation is used to demarcate transaction boundaries. It is applied to methods, indicating that the method should be wrapped in a transaction, ensuring that either all operations within the method succeed or none of them do. This is crucial for maintaining data consistency in the database.

The @PreAuthorize annotation in Spring Security allows for complex SpEL expressions to define fine-grained access control conditions. This means you can use expressions involving multiple variables and logic, making it more versatile than @Secured, which primarily works with roles.

In Spring Boot, the @PostMapping annotation is used to map HTTP POST requests onto specific handler methods in a controller class. When you apply this annotation to a method, it tells Spring that this method should be invoked when an HTTP POST request with a matching URL is received. It's a key annotation for handling POST requests in a RESTful API.

To implement a complex request mapping strategy with custom conditions, you would typically need to create a custom RequestMappingHandlerMapping. This allows you to define intricate conditions and behaviors for mapping requests to controller methods. Using annotations or configuration properties alone may not provide the level of customization needed for complex mappings. A separate utility class may not integrate seamlessly with Spring Boot's request handling mechanism.

In Spring Boot, the primary annotation used to mark the main class of your application is @SpringBootApplication. This annotation not only marks the class as the main entry point but also enables various Spring Boot features like auto-configuration, component scanning, and more. It's the starting point for your Spring Boot application.

To implement custom exception handling in a Spring Boot application with different response bodies for each exception type while ensuring unhandled exceptions are addressed, you can use the @ExceptionHandler annotation on controller methods. This approach allows you to handle specific exceptions with custom logic while ensuring unhandled exceptions are still processed. Using a global exception handler may not address specific exception types adequately.

To optimize the JVM for a Spring Boot application, you should tune garbage collection settings. Garbage collection optimization is crucial because it helps manage memory efficiently. You can adjust parameters like heap size, garbage collection algorithms, and pause times to match your application's needs. Disabling garbage collection is not a practical solution as it will lead to memory issues. Minimizing the heap size without considering application requirements can result in performance problems. Using a custom class loader may have specific use cases but isn't a general JVM optimization technique.

In Spring Boot, the "@ConditionalOnProperty" annotation is used to conditionally enable a configuration based on the presence of a specific property. This annotation allows you to configure components or beans based on the values of properties, making it a powerful tool for conditional configuration in your application.

The deleteById method of a JpaRepository deletes an entity from the database by its primary key. It is a convenient method for removing specific entities based on their unique identifier. The other options do not accurately describe the behavior of this method; in particular, it does not mark the entity as deleted without removing it from the database.