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    }