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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.util.List;
import org.apache.lucene.store.Directory;
/**
* Instances of this reader type can only be used to get stored fields from the underlying
* LeafReaders, but it is not possible to directly retrieve postings. To do that, get the {@link
* LeafReaderContext} for all sub-readers via {@link #leaves()}.
*
* IndexReader instances for indexes on disk are usually constructed with a call to one of the
* static DirectoryReader.open() methods, e.g. {@link DirectoryReader#open(Directory)}.
* {@link DirectoryReader} implements the {@code CompositeReader} interface, it is not possible to
* directly get postings.
*
*
Concrete subclasses of IndexReader are usually constructed with a call to one of the static
* open() methods, e.g. {@link DirectoryReader#open(Directory)}.
*
*
For efficiency, in this API documents are often referred to via document numbers,
* 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.
*
*
NOTE: {@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 not synchronize on the IndexReader instance; use
* your own (non-Lucene) objects instead.
*/
public abstract non-sealed class CompositeReader extends IndexReader {
private volatile CompositeReaderContext readerContext = null; // lazy init
/** Sole constructor. (For invocation by subclass constructors, typically implicit.) */
protected CompositeReader() {
super();
}
@Override
public String toString() {
final StringBuilder buffer = new StringBuilder();
// walk up through class hierarchy to get a non-empty simple name (anonymous classes have no
// name):
for (Class clazz = getClass(); clazz != null; clazz = clazz.getSuperclass()) {
if (!clazz.isAnonymousClass()) {
buffer.append(clazz.getSimpleName());
break;
}
}
buffer.append('(');
final List subReaders = getSequentialSubReaders();
assert subReaders != null;
if (!subReaders.isEmpty()) {
buffer.append(subReaders.get(0));
for (int i = 1, c = subReaders.size(); i < c; ++i) {
buffer.append(" ").append(subReaders.get(i));
}
}
buffer.append(')');
return buffer.toString();
}
/**
* Expert: returns the sequential sub readers that this reader is logically composed of. This
* method may not return {@code null}.
*
*
NOTE: In contrast to previous Lucene versions this method is no longer public, code
* that wants to get all {@link LeafReader}s this composite is composed of should use {@link
* IndexReader#leaves()}.
*
* @see IndexReader#leaves()
*/
protected abstract List getSequentialSubReaders();
@Override
public final CompositeReaderContext getContext() {
ensureOpen();
// lazy init without thread safety for perf reasons: Building the readerContext twice does not
// hurt!
if (readerContext == null) {
assert getSequentialSubReaders() != null;
readerContext = CompositeReaderContext.create(this);
}
return readerContext;
}
}