/*
* 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.analysis;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.apache.lucene.util.AttributeSource;
This class can be used if the token attributes of a TokenStream are intended to be consumed more than once. It caches all token attribute states locally in a List when the first call to incrementToken()
is called. Subsequent calls will used the cache.
Important: Like any proper TokenFilter, reset()
propagates to the input, although only before incrementToken()
is called the first time. Prior to Lucene 5, it was never propagated.
/**
* This class can be used if the token attributes of a TokenStream
* are intended to be consumed more than once. It caches
* all token attribute states locally in a List when the first call to
* {@link #incrementToken()} is called. Subsequent calls will used the cache.
* <p>
* <em>Important:</em> Like any proper TokenFilter, {@link #reset()} propagates
* to the input, although only before {@link #incrementToken()} is called the
* first time. Prior to Lucene 5, it was never propagated.
*/
public final class CachingTokenFilter extends TokenFilter {
private List<AttributeSource.State> cache = null;
private Iterator<AttributeSource.State> iterator = null;
private AttributeSource.State finalState;
Create a new CachingTokenFilter around input
. As with
any normal TokenFilter, do not call reset on the input; this filter
will do it normally.
/**
* Create a new CachingTokenFilter around <code>input</code>. As with
* any normal TokenFilter, do <em>not</em> call reset on the input; this filter
* will do it normally.
*/
public CachingTokenFilter(TokenStream input) {
super(input);
}
Propagates reset if incrementToken has not yet been called. Otherwise
it rewinds the iterator to the beginning of the cached list.
/**
* Propagates reset if incrementToken has not yet been called. Otherwise
* it rewinds the iterator to the beginning of the cached list.
*/
@Override
public void reset() throws IOException {
if (cache == null) {//first time
input.reset();
} else {
iterator = cache.iterator();
}
}
The first time called, it'll read and cache all tokens from the input. /** The first time called, it'll read and cache all tokens from the input. */
@Override
public final boolean incrementToken() throws IOException {
if (cache == null) {//first-time
// fill cache lazily
cache = new ArrayList<>(64);
fillCache();
iterator = cache.iterator();
}
if (!iterator.hasNext()) {
// the cache is exhausted, return false
return false;
}
// Since the TokenFilter can be reset, the tokens need to be preserved as immutable.
restoreState(iterator.next());
return true;
}
@Override
public final void end() {
if (finalState != null) {
restoreState(finalState);
}
}
private void fillCache() throws IOException {
while (input.incrementToken()) {
cache.add(captureState());
}
// capture final state
input.end();
finalState = captureState();
}
If the underlying token stream was consumed and cached. /** If the underlying token stream was consumed and cached. */
public boolean isCached() {
return cache != null;
}
}