org.apache.lucene.index.MultiReader.java Source code

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Here is the source code for org.apache.lucene.index.MultiReader.java

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/*
 * 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.
 */
package org.apache.lucene.index;

import java.io.IOException;

/** A {@link CompositeReader} which reads multiple indexes, appending
 *  their content. It can be used to create a view on several
 *  sub-readers (like {@link DirectoryReader}) and execute searches on it.
 * 
 * <p> For efficiency, in this API documents are often referred to via
 * <i>document numbers</i>, non-negative integers which each name a unique
 * document in the index.  These document numbers are ephemeral -- they may change
 * as documents are added to and deleted from an index.  Clients should thus not
 * rely on a given document having the same number between sessions.
 * 
 * <p><a name="thread-safety"></a><p><b>NOTE</b>: {@link
 * IndexReader} instances are completely thread
 * safe, meaning multiple threads can call any of its methods,
 * concurrently.  If your application requires external
 * synchronization, you should <b>not</b> synchronize on the
 * <code>IndexReader</code> instance; use your own
 * (non-Lucene) objects instead.
 */
public class MultiReader extends BaseCompositeReader<IndexReader> {
    private final boolean closeSubReaders;

    /**
     * <p>Construct a MultiReader aggregating the named set of (sub)readers.
     * <p>Note that all subreaders are closed if this Multireader is closed.</p>
     * @param subReaders set of (sub)readers
     */
    public MultiReader(IndexReader... subReaders) throws IOException {
        this(subReaders, true);
    }

    /**
     * <p>Construct a MultiReader aggregating the named set of (sub)readers.
     * @param subReaders set of (sub)readers; this array will be cloned.
     * @param closeSubReaders indicates whether the subreaders should be closed
     * when this MultiReader is closed
     */
    public MultiReader(IndexReader[] subReaders, boolean closeSubReaders) throws IOException {
        super(subReaders.clone());
        this.closeSubReaders = closeSubReaders;
        if (!closeSubReaders) {
            for (int i = 0; i < subReaders.length; i++) {
                subReaders[i].incRef();
            }
        }
    }

    @Override
    public CacheHelper getReaderCacheHelper() {
        // MultiReader instances can be short-lived, which would make caching trappy
        // so we do not cache on them, unless they wrap a single reader in which
        // case we delegate
        if (getSequentialSubReaders().size() == 1) {
            return getSequentialSubReaders().get(0).getReaderCacheHelper();
        }
        return null;
    }

    @Override
    protected synchronized void doClose() throws IOException {
        IOException ioe = null;
        for (final IndexReader r : getSequentialSubReaders()) {
            try {
                if (closeSubReaders) {
                    r.close();
                } else {
                    r.decRef();
                }
            } catch (IOException e) {
                if (ioe == null)
                    ioe = e;
            }
        }
        // throw the first exception
        if (ioe != null)
            throw ioe;
    }
}