In a large Spring Boot application with multiple modules, organizing and managing configuration properties efficiently can be achieved by structuring properties hierarchically, matching them to the module's package structure. This approach promotes encapsulation and ensures that each module has its own configuration properties. Placing all properties in a single file can lead to conflicts and make it challenging to track changes. Hard-coding properties lacks flexibility and maintainability. Using a version control system is important for tracking changes but doesn't address organization directly.

To use a different version of a specific dependency than the one provided by the Spring Boot Starter, you can add an exclusion for that dependency in the project's build file (build.gradle for Gradle or pom.xml for Maven). This allows you to specify your desired version while still benefiting from the other dependencies provided by the Spring Boot Starter. The other options are not the recommended approaches for version management.

The @ConditionalOnClass annotation in Spring Boot checks whether a specified class is available in the classpath. If the class is present, the associated auto-configuration is applied. This annotation plays a critical role in determining which auto-configurations are relevant based on the presence or absence of certain classes in the classpath, making it a key element in conditional auto-configuration.

The @DataJpaTest annotation is specifically designed for testing JPA (Java Persistence API) components in a Spring Boot application. It configures a slice of the application context that contains only JPA-related beans, making it suitable for JPA testing.

To enable method-level security annotations like @Secured and @PreAuthorize, you need to configure the method-security attribute in the Spring Security configuration. This attribute is set to true to enable these annotations.

To remove a single cache entry in Spring Boot, the @CacheEvictEntry annotation is used. This annotation is typically applied to methods that need to evict or remove specific cache entries. By specifying the cache name and the key(s) in this annotation, you can target and remove specific entries from the cache. It's a useful annotation for cache management.

To isolate the Data Layer while performing unit tests on Service Layer components in Spring Boot, you should use the @DataJpaTest annotation. This annotation is designed for testing JPA repositories and automatically configures a test slice of the application context limited to the data layer.

Eureka is the Spring Cloud component primarily used for service discovery. It allows microservices to find and communicate with each other dynamically.

The @Qualifier annotation in Spring is used to specify the exact bean to be injected when there are multiple candidates of the same type. This helps resolve ambiguity in cases where there are multiple beans of the same type that could be injected. By using @Qualifier with the bean's name, you can explicitly indicate which bean should be injected, ensuring that the correct one is selected. It's particularly useful when you have multiple beans of the same type and need to specify which one should be used for injection.

In this scenario, you should use two separate transactions for reading and writing. The read transaction fetches the data, and the write transaction modifies the data and commits the changes to the database. This approach ensures that changes are committed while maintaining the integrity of the database. Using read-only transactions or in-memory databases for testing would not fulfill the requirement.