Скачать или смотреть Resolving the Unknown property error in MapStruct with Lombok

Discover how to fix the MapStruct `Unknown property error` that arises when using it alongside Lombok in your Java projects. A clear, step-by-step guide awaits!
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This video is based on the question https://stackoverflow.com/q/64989206/ asked by the user 'alyssa moon' ( https://stackoverflow.com/u/13828914/ ) and on the answer https://stackoverflow.com/a/65042795/ provided by the user 'Filip' ( https://stackoverflow.com/u/1115491/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the Unknown Property Error in MapStruct with Lombok

When working with Java applications that utilize MapStruct for data mapping and Lombok for minimizing boilerplate code, developers sometimes encounter a frustrating issue: the Unknown property error. This error can halt your development progress and leave you scratching your head. In this post, we’ll explore what triggers this error and how to effectively resolve it while using both MapStruct and Lombok.

Understanding the Problem

The error message you may see looks something like this:

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

This indicates that there is a mismatch between the properties defined in your DTO (Data Transfer Object) and the target entity class. To better understand this, let’s examine the provided classes involved in the mapping process.

Entity and EntityDto Classes

Here are the relevant classes:

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

In this scenario, the EntityDto class does not have an id property, which is present in the Entity class. The attempt to map these properties hence causes confusion, triggering the error.

The Mapping Class

The issue arises from the EntityMapper interface that defines the mapping rules:

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

Here, you attempt to ignore the id property directly in the mapping, but the underlying processor is confused due to configuration issues, as indicated in the error output.

Investigating the Configuration

Upon trying various configurations, one, in particular, might work without the @ Mapping annotation yet leads to mappings where all properties are null. Here's a snippet of the generated mapping implementation as an example:

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

Evaluation of Build Configuration

In the provided build.gradle, we notice the following lines:

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

It is crucial that lombok-mapstruct-binding is placed correctly in the build configuration to work effectively with Lombok and MapStruct.

A Clear Solution

The root of the problem here lies in how Lombok’s binding for MapStruct is configured. Here’s how to fix it:

Update Your Gradle Dependencies: Move the lombok-mapstruct-binding dependency under annotationProcessor. Your updated build.gradle should look like this:

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

Recompile Your Project: After making this change, run a clean build of your project. This should resolve the unknown property issue.

Conclusion

By ensuring that the lombok-mapstruct-binding is positioned under annotationProcessor, you enable proper integration between MapStruct and Lombok. This will eliminate the Unknown property error and allow you to confidently map between your entity classes and DTOs without encountering null property mappings.

If you face similar issues in the future, just revisit your build configuration, and you’ll be able to resolve these problems without hassle! Happy coding!