    001    // Copyright 2009 The Apache Software Foundation
    002    //
    003    // Licensed under the Apache License, Version 2.0 (the "License");
    004    // you may not use this file except in compliance with the License.
    005    // You may obtain a copy of the License at
    006    //
    007    //     http://www.apache.org/licenses/LICENSE-2.0
    008    //
    009    // Unless required by applicable law or agreed to in writing, software
    010    // distributed under the License is distributed on an "AS IS" BASIS,
    011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012    // See the License for the specific language governing permissions and
    013    // limitations under the License.
    014
    015    package org.apache.tapestry5;
    016
    017    /**
    018     * Extension to {@link org.apache.tapestry5.Asset} that adds a method to determine if the asset is invariant or not.
    019     * {@link org.apache.tapestry5.services.AssetFactory} instances should ideally return Asset2 objects, not Asset. This is
    020     * only of primary interest to the {@link org.apache.tapestry5.internal.bindings.AssetBindingFactory}, as it determines
    021     * the invariance of the binding from the asset (and assumes variant unless the asset object implements this
    022     * interface).
    023     *
    024     * @since 5.1.0.0
    025     */
    026    public interface Asset2 extends Asset
    027    {
    028        /**
    029         * Returns true if the Asset is invariant (meaning that it returns the same value from {@link Asset#toClientURL()}
    030         * at all times). Most Assets are invariant. Assets that are used as binding values will be cached more aggressively by Tapestry if they are
    031         * invariant.
    032         *
    033         * @return true if invariant
    034         * @see org.apache.tapestry5.services.AssetPathConverter#isInvariant()
    035         * @see Binding#isInvariant()
    036         */
    037        boolean isInvariant();
    038    }