Java tutorial
/* * Licensed to Elasticsearch under one or more contributor * license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright * ownership. Elasticsearch 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. */ package org.elasticsearch.index.shard; import org.apache.lucene.index.DirectoryReader; import org.apache.lucene.index.FilterDirectoryReader; import org.apache.lucene.index.IndexReader; import org.apache.lucene.index.LeafReader; import org.apache.lucene.search.IndexSearcher; import org.elasticsearch.ElasticsearchException; import org.elasticsearch.common.lucene.index.ElasticsearchDirectoryReader; import org.elasticsearch.index.engine.Engine; import java.io.IOException; /** * Extension point to add custom functionality at request time to the {@link DirectoryReader} * and {@link IndexSearcher} managed by the {@link IndexShard}. */ public class IndexSearcherWrapper { /** * Wraps the given {@link DirectoryReader}. The wrapped reader can filter out document just like delete documents etc. but * must not change any term or document content. * <p> * NOTE: The wrapper has a per-request lifecycle, must delegate {@link IndexReader#getCoreCacheKey()} and must be an instance * of {@link FilterDirectoryReader} that eventually exposes the original reader via {@link FilterDirectoryReader#getDelegate()}. * The returned reader is closed once it goes out of scope. * </p> * @param reader The provided directory reader to be wrapped to add custom functionality * @return a new directory reader wrapping the provided directory reader or if no wrapping was performed * the provided directory reader */ protected DirectoryReader wrap(DirectoryReader reader) throws IOException { return reader; } /** * @param searcher The provided index searcher to be wrapped to add custom functionality * @return a new index searcher wrapping the provided index searcher or if no wrapping was performed * the provided index searcher */ protected IndexSearcher wrap(IndexSearcher searcher) throws IOException { return searcher; } /** * If there are configured {@link IndexSearcherWrapper} instances, the {@link IndexSearcher} of the provided engine searcher * gets wrapped and a new {@link Engine.Searcher} instances is returned, otherwise the provided {@link Engine.Searcher} is returned. * * This is invoked each time a {@link Engine.Searcher} is requested to do an operation. (for example search) */ public final Engine.Searcher wrap(Engine.Searcher engineSearcher) throws IOException { final ElasticsearchDirectoryReader elasticsearchDirectoryReader = ElasticsearchDirectoryReader .getElasticsearchDirectoryReader(engineSearcher.getDirectoryReader()); if (elasticsearchDirectoryReader == null) { throw new IllegalStateException("Can't wrap non elasticsearch directory reader"); } NonClosingReaderWrapper nonClosingReaderWrapper = new NonClosingReaderWrapper( engineSearcher.getDirectoryReader()); DirectoryReader reader = wrap(nonClosingReaderWrapper); if (reader != nonClosingReaderWrapper) { if (reader.getCoreCacheKey() != elasticsearchDirectoryReader.getCoreCacheKey()) { throw new IllegalStateException( "wrapped directory reader doesn't delegate IndexReader#getCoreCacheKey, wrappers must override this method and delegate" + " to the original readers core cache key. Wrapped readers can't be used as cache keys since their are used only per request which would lead to subtle bugs"); } if (ElasticsearchDirectoryReader .getElasticsearchDirectoryReader(reader) != elasticsearchDirectoryReader) { // prevent that somebody wraps with a non-filter reader throw new IllegalStateException( "wrapped directory reader hides actual ElasticsearchDirectoryReader but shouldn't"); } } final IndexSearcher origIndexSearcher = engineSearcher.searcher(); final IndexSearcher innerIndexSearcher = new IndexSearcher(reader); innerIndexSearcher.setQueryCache(origIndexSearcher.getQueryCache()); innerIndexSearcher.setQueryCachingPolicy(origIndexSearcher.getQueryCachingPolicy()); innerIndexSearcher.setSimilarity(origIndexSearcher.getSimilarity(true)); // TODO: Right now IndexSearcher isn't wrapper friendly, when it becomes wrapper friendly we should revise this extension point // For example if IndexSearcher#rewrite() is overwritten than also IndexSearcher#createNormalizedWeight needs to be overwritten // This needs to be fixed before we can allow the IndexSearcher from Engine to be wrapped multiple times final IndexSearcher indexSearcher = wrap(innerIndexSearcher); if (reader == nonClosingReaderWrapper && indexSearcher == innerIndexSearcher) { return engineSearcher; } else { return new Engine.Searcher(engineSearcher.source(), indexSearcher) { @Override public void close() throws ElasticsearchException { try { reader().close(); // we close the reader to make sure wrappers can release resources if needed.... // our NonClosingReaderWrapper makes sure that our reader is not closed } catch (IOException e) { throw new ElasticsearchException("failed to close reader", e); } finally { engineSearcher.close(); } } }; } } private static final class NonClosingReaderWrapper extends FilterDirectoryReader { private NonClosingReaderWrapper(DirectoryReader in) throws IOException { super(in, new SubReaderWrapper() { @Override public LeafReader wrap(LeafReader reader) { return reader; } }); } @Override protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) throws IOException { return new NonClosingReaderWrapper(in); } @Override protected void doClose() throws IOException { // don't close here - mimic the MultiReader#doClose = false behavior that FilterDirectoryReader doesn't have } @Override public Object getCoreCacheKey() { return in.getCoreCacheKey(); } } }