How to Hide Null Key in Payload Using MapStruct in Spring Boot

Learn how to effectively use MapStruct in Spring Boot to hide fields with null values from your JSON payload. Discover a simple solution to streamline your data responses.
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This video is based on the question https://stackoverflow.com/q/62027636/ asked by the user 'Harini Krishnan' ( https://stackoverflow.com/u/11125169/ ) and on the answer https://stackoverflow.com/a/71748976/ provided by the user 'Reza Aslejeddian' ( https://stackoverflow.com/u/13898059/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Hide Null Key in Payload Using MapStruct in Spring Boot

When working with APIs, especially in applications built with Spring Boot, it's common to face the issue of unwanted null fields appearing in the JSON responses. This can clutter the returned data and affect the efficiency of data transmission. Today, we'll discuss how to effectively hide specific keys in your payload if their values are null—specifically focusing on how to achieve this using MapStruct.

The Problem Statement

Imagine you have a data transfer object (DTO) that gets automatically generated. One of the fields, attributes, sometimes holds null values. If you were to serialize this DTO to JSON, you would end up with the following output:

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This output is not ideal. You'd usually want to avoid sending back the attributes field when it does not have a meaningful value, resulting in a cleaner and more efficient response:

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However, you're faced with a constraint: you cannot use @ JsonInclude(JsonInclude.Include.NON_NULL) in your DTO due to automatic generation processes, and you also can't enforce @ NotNull in your model since the field can genuinely be null in certain scenarios.

The Solution

Fortunately, there is a straightforward approach to address this concern effectively. Here is how you can do it:

Step 1: Use @ JsonInclude on Your Entity

Instead of applying @ JsonInclude directly on the DTO, consider placing it on the entity class that represents your data model. This will ensure that whenever your entity is serialized, any fields that are null will not be included in the output. Here’s how you can implement this:

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Step 2: Utilize MapStruct for DTO Mapping

Once you have the @ JsonInclude annotation applied to your entity, you can continue to use MapStruct for mapping your entity to DTOs. MapStruct will seamlessly carry over this configuration, ensuring that null values are excluded when mapping occurs.

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Benefits of This Approach

Cleaner JSON Output: Null fields are effortlessly excluded, providing a more streamlined response.

Reduced Network Traffic: Sending smaller payloads due to omitted null values means your API is more efficient.

Seamless Integration with Auto-Generated DTOs: Since the modifications take place at the entity level, your auto-generated DTOs remain untouched.

Conclusion

In summary, if you need to hide keys with null values in your payloads while working with MapStruct in Spring Boot, the best approach is to apply the @ JsonInclude(JsonInclude.Include.NON_NULL) annotation to your entity class. This allows for a clean and efficient API response without interfering with your DTO generation process.

By following these steps, you can maintain a clean payload while dealing with optional fields effectively. Happy coding!

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