Скачать или смотреть How to Configure MapStruct to Ignore Object Mapping When All Fields Are Null

This guide guides you on how to configure MapStruct to return `null` when all fields of the source object are `null`, streamlining your data mapping process.
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How to Configure MapStruct to Ignore Object Mapping When All Fields Are Null

In the realm of Java development, particularly when working with data transfer objects (DTOs) and entity mappings, developers often face the question: How can we effectively manage object mappings in MapStruct when all fields of the source object are null? This is a common scenario that can lead to undesired instances of creating new objects that hold no meaningful data. Here’s a detailed look at how to approach this problem effectively.

The Problem at Hand

Imagine you have a situation where you need to map a WealthProdAccountInfoDTO to an AgentInfo object. However, you want to avoid creating a new AgentInfo instance if all fields in the DTO are null. By default, MapStruct will generate a method that returns an AgentInfo object even if all the input fields are null, which is not ideal.

Below is the default generated code for mapping, which showcases this scenario:

[[See Video to Reveal this Text or Code Snippet]]

The Solution

To address this issue, you will need to implement some additional logic within your mapping process. Here’s a step-by-step guide to modifying your MapStruct configuration to return null when all fields of the source object are null:

Step 1: Use the @ AfterMapping Annotation

The first step involves using the @ AfterMapping annotation to execute custom logic right after the standard mapping is complete. This allows you to check whether all fields in the mapped object are null:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Implement the isAllFieldNull Method

Next, implement a method that checks if all fields in the mapped object are null. This method will use reflection to iterate through the fields of the object:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Retrieve Field Values with getFieldsValue

Lastly, implement a utility method that retrieves the field values of the object using reflection. This allows your isAllFieldNull method to check if indeed every field is null:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By implementing the solution outlined above, you can effectively manage the mapping of DTOs without cluttering your application with unnecessary empty objects. This approach not only enhances the performance but also keeps your object integrity intact. The use of @ AfterMapping combined with reflection provides a robust mechanism for ensuring your application behaves as expected when dealing with null objects in Java.

Utilizing MapStruct in this manner can streamline your mapping processes, making for cleaner and more efficient code. Happy coding!