[FEATURE] Create custom inline and class based annotations

[poloka]

Before submitting
Please check our wiki because some feature requests are asked a lot and there are good reasons (as explained on the wiki) why we can't (yet) implement them or why we won't implement them.

Describe the feature
The request to add the ability to create custom annotations will significantly decrease the boilerplate code required to perform validations for instance/class member variables and function signatures. This request has two parts.

1. Allow creation of a custom annotation (ie: @Positive, @GreaterThanZero, @FooBar, etc) in a very simple manner without the need for a lot of boilerplate code making custom annotations a first class supported concept.
2. Allow custom inline annotations to maybe check a simple check on the fly (ie: @Custom { val > 0 }).

Describe the target audience
Audience would be anyone who want to reduce the boilerplate code for performing simple validations within their code.

Additional context
Add any other context about the feature / enhancement here.

[aayushghimirey]

If I understand correctly, you’re asking Lombok to generate validation logic at compile time. While that could save some code, it doesn’t really fit Lombok’s design:

Lombok isn’t meant for creating custom annotations easily. Each one would require complex integration with the compiler.

For things like @Positive or @GreaterThanZero (and many others), Jakarta Bean Validation is the standard. Lombok mainly handles structural code like getters and setters, not validation logic.

If you want an example of handling custom validations, check out my hibernate-postgres-rls project.

Extremely sorry if I’m wrong or have misunderstood your issue!

[poloka]

My understanding of Lombok is that it's designed to reduce boilerplate code. While it does offer features like @NonNull for getters and setters to ensure values aren’t null, I’m curious why there isn’t a straightforward way to create custom annotations for setters. The claim that this requires complex integration suggests the underlying logic might be overly complicated and could benefit from simplification. I was under the impression that Jakarta required more setup to throw exceptions; specifically, I’d like exceptions (such as IllegalArgumentExceptions) to be thrown from my getters when my validation fails. It seems like an oversight that there isn’t an easy mechanism for creating custom annotations to eliminate boilerplate code. While I understand this might not be trivial to implement, pushing that complexity onto end users is not ideal. Also, could you share a link to your project for further review?

[aayushghimirey]

Lombok’s @nonnull is a built-in feature implemented directly in Lombok’s compiler, not a general extension mechanism for user-defined validation annotations.

Lombok mainly focuses on reducing structural boilerplate like getters, setters, constructors, and builders. It’s not intended to handle business or domain-specific validation logic. For that kind of validation, using a validation framework or writing explicit code is the usual and supported approach.

For reference, I’ve worked on a project where I handle startup-time validation while integrating PostgreSQL RLS with JPA using annotations:
https://github.com/aayushghimirey/jpa-postgres-rls

A similar pattern could be used to build custom validation setups outside of Lombok.