javax.validation.Constraint Maven / Gradle / Ivy
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*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
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*/
package javax.validation;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import javax.validation.constraintvalidation.SupportedValidationTarget;
import javax.validation.constraintvalidation.ValidationTarget;
import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
/**
* Marks an annotation as being a Bean Validation constraint.
*
* A given constraint annotation must be annotated by a {@code @Constraint}
* annotation which refers to its list of constraint validation implementations.
*
* Each constraint annotation must host the following attributes:
*
* - {@code String message() default [...];} which should default to an error
* message key made of the fully-qualified class name of the constraint followed by
* {@code .message}. For example {@code "{com.acme.constraints.NotSafe.message}"}
* - {@code Class[] groups() default {};} for user to customize the targeted
* groups
* - {@code Class[] payload() default {};} for
* extensibility purposes
*
*
* When building a constraint that is both generic and cross-parameter, the constraint
* annotation must host the {@code validationAppliesTo()} property.
* A constraint is generic if it targets the annotated element and is cross-parameter if
* it targets the array of parameters of a method or constructor.
*
* ConstraintTarget validationAppliesTo() default ConstraintTarget.IMPLICIT;
*
* This property allows the constraint user to choose whether the constraint
* targets the return type of the executable or its array of parameters.
*
* A constraint is both generic and cross-parameter if
*
* - two kinds of {@code ConstraintValidator}s are attached to the
* constraint, one targeting {@link ValidationTarget#ANNOTATED_ELEMENT}
* and one targeting {@link ValidationTarget#PARAMETERS},
* - or if a {@code ConstraintValidator} targets both
* {@code ANNOTATED_ELEMENT} and {@code PARAMETERS}.
*
*
* Such dual constraints are rare. See {@link SupportedValidationTarget} for more info.
*
* Here is an example of constraint definition:
*
* @Documented
* @Constraint(validatedBy = OrderNumberValidator.class)
* @Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
* @Retention(RUNTIME)
* public @interface OrderNumber {
* String message() default "{com.acme.constraint.OrderNumber.message}";
* Class[] groups() default {};
* Class[] payload() default {};
* }
*
*
* @author Emmanuel Bernard
* @author Gavin King
* @author Hardy Ferentschik
*/
@Documented
@Target({ ANNOTATION_TYPE })
@Retention(RUNTIME)
public @interface Constraint {
/**
* {@link ConstraintValidator} classes must reference distinct target types
* for a given {@link ValidationTarget}
* If two {@code ConstraintValidator}s refer to the same type,
* an exception will occur.
*
* At most one {@code ConstraintValidator} targeting the array of parameters of
* methods or constructors (aka cross-parameter) is accepted. If two or more
* are present, an exception will occur.
*
* @return array of (@code ConstraintValidator} classes implementing the constraint
*/
Class>[] validatedBy();
}