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Lucene example source code file (TermScorer.java)
This example Lucene source code file (TermScorer.java) is included in the DevDaily.com
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The Lucene TermScorer.java source code
package org.apache.lucene.search;
/**
* 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 org.apache.lucene.index.TermDocs;
/** Expert: A <code>Scorer for documents matching a Term .
*/
final class TermScorer extends Scorer {
private TermDocs termDocs;
private byte[] norms;
private float weightValue;
private int doc = -1;
private int freq;
private final int[] docs = new int[32]; // buffered doc numbers
private final int[] freqs = new int[32]; // buffered term freqs
private int pointer;
private int pointerMax;
private static final int SCORE_CACHE_SIZE = 32;
private float[] scoreCache = new float[SCORE_CACHE_SIZE];
/**
* Construct a <code>TermScorer.
*
* @param weight
* The weight of the <code>Term in the query.
* @param td
* An iterator over the documents matching the <code>Term.
* @param similarity
* The </code>Similarity implementation to be used for score
* computations.
* @param norms
* The field norms of the document fields for the <code>Term.
*/
TermScorer(Weight weight, TermDocs td, Similarity similarity, byte[] norms) {
super(similarity, weight);
this.termDocs = td;
this.norms = norms;
this.weightValue = weight.getValue();
for (int i = 0; i < SCORE_CACHE_SIZE; i++)
scoreCache[i] = getSimilarity().tf(i) * weightValue;
}
@Override
public void score(Collector c) throws IOException {
score(c, Integer.MAX_VALUE, nextDoc());
}
// firstDocID is ignored since nextDoc() sets 'doc'
@Override
protected boolean score(Collector c, int end, int firstDocID) throws IOException {
c.setScorer(this);
while (doc < end) { // for docs in window
c.collect(doc); // collect score
if (++pointer >= pointerMax) {
pointerMax = termDocs.read(docs, freqs); // refill buffers
if (pointerMax != 0) {
pointer = 0;
} else {
termDocs.close(); // close stream
doc = Integer.MAX_VALUE; // set to sentinel value
return false;
}
}
doc = docs[pointer];
freq = freqs[pointer];
}
return true;
}
@Override
public int docID() { return doc; }
@Override
public float freq() {
return freq;
}
/**
* Advances to the next document matching the query. <br>
* The iterator over the matching documents is buffered using
* {@link TermDocs#read(int[],int[])}.
*
* @return the document matching the query or NO_MORE_DOCS if there are no more documents.
*/
@Override
public int nextDoc() throws IOException {
pointer++;
if (pointer >= pointerMax) {
pointerMax = termDocs.read(docs, freqs); // refill buffer
if (pointerMax != 0) {
pointer = 0;
} else {
termDocs.close(); // close stream
return doc = NO_MORE_DOCS;
}
}
doc = docs[pointer];
freq = freqs[pointer];
return doc;
}
@Override
public float score() {
assert doc != -1;
float raw = // compute tf(f)*weight
freq < SCORE_CACHE_SIZE // check cache
? scoreCache[freq] // cache hit
: getSimilarity().tf(freq)*weightValue; // cache miss
return norms == null ? raw : raw * getSimilarity().decodeNormValue(norms[doc]); // normalize for field
}
/**
* Advances to the first match beyond the current whose document number is
* greater than or equal to a given target. <br>
* The implementation uses {@link TermDocs#skipTo(int)}.
*
* @param target
* The target document number.
* @return the matching document or NO_MORE_DOCS if none exist.
*/
@Override
public int advance(int target) throws IOException {
// first scan in cache
for (pointer++; pointer < pointerMax; pointer++) {
if (docs[pointer] >= target) {
freq = freqs[pointer];
return doc = docs[pointer];
}
}
// not found in cache, seek underlying stream
boolean result = termDocs.skipTo(target);
if (result) {
pointerMax = 1;
pointer = 0;
docs[pointer] = doc = termDocs.doc();
freqs[pointer] = freq = termDocs.freq();
} else {
doc = NO_MORE_DOCS;
}
return doc;
}
/** Returns a string representation of this <code>TermScorer. */
@Override
public String toString() { return "scorer(" + weight + ")"; }
}
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