resource-predicates/src/main/java/org/apache/sling/resource/predicates/ChildResourcePredicates.java

/*
 * 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.
 */
package org.apache.sling.resource.predicates;

import java.util.Objects;
import java.util.function.Predicate;

import org.apache.sling.api.resource.Resource;

/**
 * Predicates that are to be used against a child resource
 * 
 *
 */
public class ChildResourcePredicates {

    private final String name;

    private ChildResourcePredicates(String name) {
        this.name = Objects.requireNonNull(name, "name value may not be null");
    }

    /**
     * Instantiates a ChildResourcePredicate object to provide the application of
     * Predicates against the named child
     * 
     * @param name
     *            of the expected child resource
     * @return Object providing helper predicates for a child resource
     */
    public static ChildResourcePredicates child(String name) {
        return new ChildResourcePredicates(name);
    }

    /**
     * Applies a predicate against the named child resource. The returned predicate
     * will always return 'false' for a child that doesn't exist
     * 
     * @param predicate
     *            to be used against the child resource
     * @return Predicate which will apply the given predicate to the child resource
     */
    public Predicate<Resource> has(Predicate<Resource> predicate) {
        Objects.requireNonNull(predicate, "predicate may not be null");
        return resource -> {
            Resource child = resource.getChild(name);
            if (child != null) {
                return predicate.test(child);
            }
            return false;
        };
    }

}