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* Copyright 2009, Red Hat, Inc. and/or its affiliates, and individual contributors
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
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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(); }





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