001 // Copyright 2010, 2011 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.internal.services;
016
017 import org.apache.tapestry5.func.F;
018 import org.apache.tapestry5.func.Mapper;
019 import org.apache.tapestry5.internal.structure.Page;
020 import org.apache.tapestry5.ioc.internal.util.CollectionFactory;
021 import org.apache.tapestry5.services.InvalidationListener;
022 import org.apache.tapestry5.services.pageload.ComponentRequestSelectorAnalyzer;
023 import org.apache.tapestry5.services.pageload.ComponentResourceSelector;
024
025 import java.lang.ref.SoftReference;
026 import java.util.Map;
027 import java.util.Set;
028
029 public class PageSourceImpl implements PageSource, InvalidationListener
030 {
031 private final ComponentRequestSelectorAnalyzer selectorAnalyzer;
032
033 private final PageLoader pageLoader;
034
035 private static final class CachedPageKey
036 {
037 final String pageName;
038
039 final ComponentResourceSelector selector;
040
041 public CachedPageKey(String pageName, ComponentResourceSelector selector)
042 {
043 this.pageName = pageName;
044 this.selector = selector;
045 }
046
047 public int hashCode()
048 {
049 return 37 * pageName.hashCode() + selector.hashCode();
050 }
051
052 public boolean equals(Object obj)
053 {
054 if (this == obj)
055 return true;
056
057 if (!(obj instanceof CachedPageKey))
058 return false;
059
060 CachedPageKey other = (CachedPageKey) obj;
061
062 return pageName.equals(other.pageName) && selector.equals(other.selector);
063 }
064 }
065
066 private final Map<CachedPageKey, SoftReference<Page>> pageCache = CollectionFactory.newConcurrentMap();
067
068 public PageSourceImpl(PageLoader pageLoader, ComponentRequestSelectorAnalyzer selectorAnalyzer)
069 {
070 this.pageLoader = pageLoader;
071 this.selectorAnalyzer = selectorAnalyzer;
072 }
073
074 public void objectWasInvalidated()
075 {
076 clearCache();
077 }
078
079 public Page getPage(String canonicalPageName)
080 {
081 ComponentResourceSelector selector = selectorAnalyzer.buildSelectorForRequest();
082
083 CachedPageKey key = new CachedPageKey(canonicalPageName, selector);
084
085 // The while loop looks superfluous, but it helps to ensure that the Page instance,
086 // with all of its mutable construction-time state, is properly published to other
087 // threads (at least, as I understand Brian Goetz's explanation, it should be).
088
089 while (true)
090 {
091 SoftReference<Page> ref = pageCache.get(key);
092
093 Page page = ref == null ? null : ref.get();
094
095 if (page != null)
096 {
097 return page;
098 }
099
100 // In rare race conditions, we may see the same page loaded multiple times across
101 // different threads. The last built one will "evict" the others from the page cache,
102 // and the earlier ones will be GCed.
103
104 page = pageLoader.loadPage(canonicalPageName, selector);
105
106 ref = new SoftReference<Page>(page);
107
108 pageCache.put(key, ref);
109 }
110 }
111
112 public void clearCache()
113 {
114 pageCache.clear();
115 }
116
117 public Set<Page> getAllPages()
118 {
119 return F.flow(pageCache.values()).map(new Mapper<SoftReference<Page>, Page>()
120 {
121 public Page map(SoftReference<Page> element)
122 {
123 return element.get();
124 }
125 }).removeNulls().toSet();
126 }
127 }