    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
    015package 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 */
    026public 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}