001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.wicket.request.resource.caching.version; 018 019import java.time.Instant; 020import java.util.regex.Pattern; 021import org.apache.wicket.request.resource.caching.IStaticCacheableResource; 022import org.apache.wicket.util.resource.IResourceStream; 023 024/** 025 * Uses the last modified timestamp of a {@link org.apache.wicket.request.resource.caching.IStaticCacheableResource} 026 * converted to milliseconds as a version string. 027 * 028 * @author Peter Ertl 029 * 030 * @since 1.5 031 */ 032public class LastModifiedResourceVersion implements IResourceVersion 033{ 034 /** 035 * A valid pattern is a sequence of digits 036 */ 037 private static final Pattern TIMESTAMP_PATTERN = Pattern.compile("[0-9]+"); 038 039 @Override 040 public String getVersion(IStaticCacheableResource resource) 041 { 042 // get last modified timestamp of resource 043 IResourceStream stream = resource.getResourceStream(); 044 045 // if resource stream can not be found do not cache 046 if (stream == null) 047 { 048 return null; 049 } 050 051 final Instant lastModified = stream.lastModifiedTime(); 052 053 // if no timestamp is available we can not provide a version 054 if (lastModified == null) 055 { 056 return null; 057 } 058 // version string = last modified timestamp converted to milliseconds 059 return String.valueOf(lastModified.toEpochMilli()).intern(); 060 } 061 062 @Override 063 public Pattern getVersionPattern() 064 { 065 return TIMESTAMP_PATTERN; 066 } 067}