Quarkus Skill

Bean Validation Annotations

• Use constraints from jakarta.validation.constraints/org.hibernate.validator.constraints packages, e.g. @NotNull, @NotBlank, @NotEmpty, @Size, @Min, @Max, @Email, @Pattern on class fields and getters or on method parameters and return values of CDI beans.
• Use @Valid for cascading validation: on bean properties or method's return value/parameters represented by a complex type with constraints.
• Place constraints on REST endpoint parameters for automatic 400 responses.

REST Integration

• Constraint violations on REST endpoint parameters automatically return HTTP 400 with validation details.
• Annotate request body DTOs with constraints, and use @Valid on the endpoint parameter.
• Return value validation and service method validation result in HTTP 500, not 400 — handle ConstraintViolationException explicitly if you need custom error responses for those.

Custom Validators

• For simple constraints that are only applicable to the current type consider creating a simple boolean getter constrained with @AssertTrue: @AssertTrue(message="{message.key.for.this.check}") public boolean is[NameOfTheCheck]() { ... }
• For reusable constraints:
  • Create a constraint annotation with @Target({ METHOD, FIELD, ... }) @Retention(RUNTIME) @Constraint(validatedBy = {}).
  • Implement ConstraintValidator<MyAnnotation, TargetType>.
  • Add a FQCN of the implemented constraint validator to the service file src/main/resources/META-INF/services/jakarta.validation.ConstraintValidator

Method Validation

• Annotate CDI bean method parameters and return values with constraints.
• Method validation is automatic for CDI beans — no extra config needed.

Testing

• Test validation by sending invalid input via REST Assured and asserting 400 status.
• For unit testing validators, use Validator injection and validator.validate(object).

Common Pitfalls

• Do NOT forget @Valid on nested object parameters — Without it, constraints on nested object fields are silently ignored.
• Automatic method parameter/return value validation only works on CDI-managed beans — any method calls on plain new objects are not validated.