Скачать или смотреть Properly Mapping Multiple Level Inheritance in Java using Lombok and MapStruct

Learn how to efficiently map classes with multiple levels of inheritance in Java using Lombok and MapStruct, ensuring type safety and seamless data transformations.
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Properly Mapping Multiple Level Inheritance in Java

When working with object-oriented programming in Java, developers often encounter the concept of inheritance. Specifically, multiple level inheritance involves a class inheriting from another class that has also inherited from a different class. This scenario can quickly become complicated, especially when mapping these objects to database entities or data transfer objects. In this post, we’ll explore how to effectively map classes with multiple levels of inheritance using Lombok and MapStruct.

The Challenge

Consider the following structure where we have a Store class containing a list of Pet objects. These Pet objects can be of various types (e.g., Cat, Dog, Pig), each defined as a subclass of the Pet class. The primary challenge here is how to map this hierarchy into a format suitable for database storage or API responses.

Example Class Definitions

Here are the relevant class definitions that outline the structure of our objects:

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Requirement for Mapping

The goal is to create mappers that can translate Store and Pet objects to their respective database representations (StoreEntity and PetEntity). However, because of the inheritance hierarchy, simply creating separate mappers for Pet can lead to issues where the logic may get overwritten.

The Solution

The solution involves using a single mapper interface that adheres to MapStruct's capabilities while also handling the mapping logic for the inherited classes by using default methods.

Mapper Interface Example

Here’s an implementation of the mapper interface that handles the complex inheritance:

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Key Takeaways

Single Mapper Approach: We maintain one mapper for both Store and Pet classes to simplify the mapping logic and avoid conflicts.

Default Methods for Type Handling: Using default methods in the mapper interface allows us to create custom mapping logic while adhering to MapStruct's powerful mapping capabilities.

Explicit Type Checks: We check the type of Pet instances when converting to PetEntity, ensuring accurate mapping based on the actual object type rather than relying on automated behavior.

Conclusion

By following the outlined approach, developers can successfully map complex hierarchical structures in Java while keeping the code organized and manageable. Utilizing Lombok and MapStruct not only simplifies the boilerplate code inherent in Java applications but also enhances readability and maintainability.

Embrace this structured approach to ensure your data remains consistent and accurately represented throughout your application layers!