java / expert
Snippet
Custom Constraint Validators for Complex Domain Logic
Beyond simple field validation, Spring supports class-level constraints via ConstraintValidator. This allows for complex validation logic involving multiple fields within an object, maintaining domain integrity.
snippet.java
java
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public class PasswordMatchesValidator implements ConstraintValidator<PasswordMatches, UserDto> {@Overridepublic boolean isValid(UserDto user, ConstraintValidatorContext context) {return user.getPassword().equals(user.getMatchingPassword());}}@Target({TYPE, ANNOTATION_TYPE})@Retention(RUNTIME)@Constraint(validatedBy = PasswordMatchesValidator.class)public @interface PasswordMatches {String message() default "Passwords don't match";Class<?>[] groups() default {};Class<? extends Payload>[] payload() default {};}
spring
Breakdown
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implements ConstraintValidator<PasswordMatches, UserDto>
Links the custom annotation to the logic that validates the specific DTO.
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@Constraint(validatedBy = PasswordMatchesValidator.class)
The annotation metadata that points Spring to the implementation class for validation logic.
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user.getPassword().equals(user.getMatchingPassword())
The actual business logic comparing two fields within the DTO.