package org.apache.lucene.index;
/**
* 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.
*/
import java.io.IOException;
import java.util.List;
import java.util.ArrayList;
import org.apache.lucene.util.Bits;
import org.apache.lucene.util.ReaderUtil;
/**
* This class forces a composite reader (eg a {@link
* MultiReader} or {@link DirectoryReader} or any other
* IndexReader subclass that returns non-null from {@link
* IndexReader#getSequentialSubReaders}) to emulate an
* atomic reader. This requires implementing the postings
* APIs on-the-fly, using the static methods in {@link
* MultiFields}, by stepping through the sub-readers to
* merge fields/terms, appending docs, etc.
*
* <p>If you ever hit an UnsupportedOperationException saying
* "please use MultiFields.XXX instead", the simple
* but non-performant workaround is to wrap your reader
* using this class.</p>
*
* <p><b>NOTE</b>: this class almost always results in a
* performance hit. If this is important to your use case,
* it's better to get the sequential sub readers (see {@link
* ReaderUtil#gatherSubReaders}, instead, and iterate through them
* yourself.</p>
*/
public final class SlowMultiReaderWrapper extends FilterIndexReader {
/** This method may return the reader back, if the
* incoming reader is already atomic. */
public static IndexReader wrap(IndexReader reader) throws IOException {
final List<IndexReader> subs = new ArrayList<IndexReader>();
ReaderUtil.gatherSubReaders(subs, reader);
if (subs == null) {
// already an atomic reader
return reader;
} else if (subs.size() == 1) {
return subs.get(0);
} else {
return new SlowMultiReaderWrapper(reader);
}
}
private SlowMultiReaderWrapper(IndexReader other) throws IOException {
super(other);
}
@Override
public Fields fields() throws IOException {
return MultiFields.getFields(in);
}
@Override
public Bits getDeletedDocs() {
return MultiFields.getDeletedDocs(in);
}
@Override
public void doClose() throws IOException {
throw new UnsupportedOperationException("please call close on the original reader instead");
}
}