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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.solr.ltr.feature;

import java.io.IOException;
import java.util.LinkedHashMap;
import java.util.Map;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.NumericDocValues;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.util.SmallFloat;
import org.apache.solr.request.SolrQueryRequest;

/**
 * This feature returns the length of a field (in terms) for the current document. Example
 * configuration:
 *
 * 
 * {
 *   "name":  "titleLength",
 *   "class": "org.apache.solr.ltr.feature.FieldLengthFeature",
 *   "params": {
 *     "field": "title"
 *   }
 * }
 * 
* * Note: since this feature relies on norms values that are stored in a single byte the value of the * feature could have a lightly different value. (see also {@link * org.apache.lucene.search.similarities.ClassicSimilarity}) */ public class FieldLengthFeature extends Feature { private String field; public String getField() { return field; } public void setField(String field) { this.field = field; } @Override public LinkedHashMap paramsToMap() { final LinkedHashMap params = defaultParamsToMap(); params.put("field", field); return params; } @Override protected void validate() throws FeatureException { if (field == null || field.isEmpty()) { throw new FeatureException(getClass().getSimpleName() + ": field must be provided"); } } /** Cache of decoded bytes. */ private static final float[] NORM_TABLE = new float[256]; static { NORM_TABLE[0] = 0; for (int i = 1; i < 256; i++) { NORM_TABLE[i] = SmallFloat.byte4ToInt((byte) i); } } /** Decodes the norm value, assuming it is a single byte. */ private final float decodeNorm(long norm) { return NORM_TABLE[(int) (norm & 0xFF)]; // & 0xFF maps negative bytes to // positive above 127 } public FieldLengthFeature(String name, Map params) { super(name, params); } @Override public FeatureWeight createWeight( IndexSearcher searcher, boolean needsScores, SolrQueryRequest request, Query originalQuery, Map efi) throws IOException { return new FieldLengthFeatureWeight(searcher, request, originalQuery, efi); } public class FieldLengthFeatureWeight extends FeatureWeight { public FieldLengthFeatureWeight( IndexSearcher searcher, SolrQueryRequest request, Query originalQuery, Map efi) { super(FieldLengthFeature.this, searcher, request, originalQuery, efi); } @Override public FeatureScorer scorer(LeafReaderContext context) throws IOException { NumericDocValues norms = context.reader().getNormValues(field); if (norms == null) { return new ValueFeatureScorer( this, 0f, DocIdSetIterator.all(DocIdSetIterator.NO_MORE_DOCS)); } return new FieldLengthFeatureScorer(this, norms); } public class FieldLengthFeatureScorer extends FeatureScorer { NumericDocValues norms = null; public FieldLengthFeatureScorer(FeatureWeight weight, NumericDocValues norms) { super(weight, norms); this.norms = norms; } @Override public float score() throws IOException { final long l = norms.longValue(); final float numTerms = decodeNorm(l); return numTerms; } @Override public float getMaxScore(int upTo) throws IOException { return Float.POSITIVE_INFINITY; } } } }




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