pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / contrib / xml-query-parser / src / java / org / apache / lucene / xmlparser / builders / CachedFilterBuilder.java

diff --git a/lucene-java-3.5.0/lucene/contrib/xml-query-parser/src/java/org/apache/lucene/xmlparser/builders/CachedFilterBuilder.java b/lucene-java-3.5.0/lucene/contrib/xml-query-parser/src/java/org/apache/lucene/xmlparser/builders/CachedFilterBuilder.java
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+++ b/lucene-java-3.5.0/lucene/contrib/xml-query-parser/src/java/org/apache/lucene/xmlparser/builders/CachedFilterBuilder.java
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+/*
+ * Created on 25-Jan-2006
+ */
+package org.apache.lucene.xmlparser.builders;
+
+import java.util.Map.Entry;
+
+import org.apache.lucene.search.CachingWrapperFilter;
+import org.apache.lucene.search.Filter;
+import org.apache.lucene.search.Query;
+import org.apache.lucene.search.QueryWrapperFilter;
+import org.apache.lucene.xmlparser.DOMUtils;
+import org.apache.lucene.xmlparser.FilterBuilder;
+import org.apache.lucene.xmlparser.FilterBuilderFactory;
+import org.apache.lucene.xmlparser.ParserException;
+import org.apache.lucene.xmlparser.QueryBuilder;
+import org.apache.lucene.xmlparser.QueryBuilderFactory;
+import org.w3c.dom.Element;
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * Filters are cached in an LRU Cache keyed on the contained query or filter object. Using this will 
+ * speed up overall performance for repeated uses of the same expensive query/filter. The sorts of 
+ * queries/filters likely to benefit from caching need not necessarily be complex - e.g. simple 
+ * TermQuerys with a large DF (document frequency) can be expensive    on large indexes. 
+ * A good example of this might be a term query on a field with only 2 possible        values - 
+ * "true" or "false". In a large index, querying or filtering on this field requires reading 
+ * millions    of document ids from disk which can more usefully be cached as a filter bitset.
+ * 
+ * For Queries/Filters to be cached and reused the object must implement hashcode and
+ * equals methods correctly so that duplicate queries/filters can be detected in the cache.
+ * 
+ * The CoreParser.maxNumCachedFilters property can be used to control the size of the LRU 
+ * Cache established during the construction of CoreParser instances.
+ *
+ */
+public class CachedFilterBuilder implements FilterBuilder {
+
+       private QueryBuilderFactory queryFactory;
+       private FilterBuilderFactory filterFactory;
+       
+    private  LRUCache<Object,Filter> filterCache = null;
+
+       private int cacheSize;
+
+       public CachedFilterBuilder(QueryBuilderFactory queryFactory, 
+                       FilterBuilderFactory filterFactory,int cacheSize)
+       {
+               this.queryFactory=queryFactory;
+               this.filterFactory=filterFactory;
+               this.cacheSize=cacheSize;
+       }
+
+       public synchronized Filter getFilter(Element e) throws ParserException
+       {
+
+               Element childElement = DOMUtils.getFirstChildOrFail(e);
+
+               if (filterCache == null)
+               {
+                       filterCache = new LRUCache<Object,Filter>(cacheSize);
+               }
+
+               // Test to see if child Element is a query or filter that needs to be
+               // cached
+               QueryBuilder qb = queryFactory.getQueryBuilder(childElement.getNodeName());
+               Object cacheKey = null;
+               Query q = null;
+               Filter f = null;
+               if (qb != null)
+               {
+                       q = qb.getQuery(childElement);
+                       cacheKey = q;
+               } else
+               {
+                       f = filterFactory.getFilter(childElement);
+                       cacheKey = f;
+               }
+               Filter cachedFilter = filterCache.get(cacheKey);
+               if (cachedFilter != null)
+               {
+                       return cachedFilter; // cache hit
+               }
+               
+               //cache miss
+               if (qb != null)
+               {
+                       cachedFilter = new QueryWrapperFilter(q);
+               } else
+               {
+                       cachedFilter = new CachingWrapperFilter(f);
+               }
+
+               filterCache.put(cacheKey, cachedFilter);
+               return cachedFilter;
+       }
+       
+       static class LRUCache<K,V> extends java.util.LinkedHashMap<K,V>
+       {
+           public LRUCache(int maxsize)
+           {
+               super(maxsize * 4 / 3 + 1, 0.75f, true);
+               this.maxsize = maxsize;
+           }
+
+           protected int maxsize;
+
+           @Override
+           protected boolean removeEldestEntry(Entry<K,V> eldest)
+           {
+               return size() > maxsize;
+           }
+
+       }
+
+}