Find a single java.lang.annotation.Annotation of annotation Type from the supplied Class , traversing its interfaces and superclasses if no annotation can be found on the given class itself. - Java java.lang.annotation

Java examples for java.lang.annotation:Class Annotation

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Description

Find a single java.lang.annotation.Annotation of annotation Type from the supplied Class , traversing its interfaces and superclasses if no annotation can be found on the given class itself.

Demo Code

/*//from   w w  w.  j a  v a  2 s  .  c  o m
 * Copyright 2002-2010 the original author or authors.
 *
 * 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
 * limitations under the License.
 */
import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;

public class Main{

    /**
     * Find a single {@link java.lang.annotation.Annotation} of <code>annotationType</code> from the supplied {@link Class},
     * traversing its interfaces and superclasses if no annotation can be found on the given class itself.
     * <p>This method explicitly handles class-level annotations which are not declared as
     * {@link java.lang.annotation.Inherited inherited} <i>as well as annotations on interfaces</i>.
     * <p>The algorithm operates as follows: Searches for an annotation on the given class and returns
     * it if found. Else searches all interfaces that the given class declares, returning the annotation
     * from the first matching candidate, if any. Else proceeds with introspection of the superclass
     * of the given class, checking the superclass itself; if no annotation found there, proceeds
     * with the interfaces that the superclass declares. Recursing up through the entire superclass
     * hierarchy if no match is found.
     * @param clazz the class to look for annotations on
     * @param annotationType the annotation class to look for
     * @return the annotation found, or <code>null</code> if none found
     */
    public static <A extends Annotation> A findAnnotation(Class<?> clazz,
            Class<A> annotationType) {
        Assert.notNull(clazz, "Class must not be null");
        A annotation = clazz.getAnnotation(annotationType);
        if (annotation != null) {
            return annotation;
        }
        for (Class<?> ifc : clazz.getInterfaces()) {
            annotation = findAnnotation(ifc, annotationType);
            if (annotation != null) {
                return annotation;
            }
        }
        if (!Annotation.class.isAssignableFrom(clazz)) {
            for (Annotation ann : clazz.getAnnotations()) {
                annotation = findAnnotation(ann.annotationType(),
                        annotationType);
                if (annotation != null) {
                    return annotation;
                }
            }
        }
        Class<?> superClass = clazz.getSuperclass();
        if (superClass == null || superClass == Object.class) {
            return null;
        }
        return findAnnotation(superClass, annotationType);
    }
}

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