kaist.irproject.lucene.trec.DocNameExtractor.java Source code

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Here is the source code for kaist.irproject.lucene.trec.DocNameExtractor.java

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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 kaist.irproject.lucene.trec;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.StoredFieldVisitor;
import org.apache.lucene.search.IndexSearcher;

/**
 * Utility: extract doc names from an index
 */
public class DocNameExtractor {

    private final String docNameField;

    /**
     * Constructor for DocNameExtractor.
     * @param docNameField name of the stored field containing the doc name. 
     */
    public DocNameExtractor(final String docNameField) {
        this.docNameField = docNameField;
    }

    /**
     * Extract the name of the input doc from the index.
     * @param searcher access to the index.
     * @param docid ID of doc whose name is needed.
     * @return the name of the input doc as extracted from the index.
     * @throws IOException if cannot extract the doc name from the index.
     */
    public String docName(IndexSearcher searcher, int docid) throws IOException {
        final List<String> name = new ArrayList<>();
        searcher.getIndexReader().document(docid, new StoredFieldVisitor() {
            @Override
            public void stringField(FieldInfo fieldInfo, String value) {
                name.add(value);
            }

            @Override
            public Status needsField(FieldInfo fieldInfo) {
                if (!name.isEmpty()) {
                    return Status.STOP;
                } else if (fieldInfo.name.equals(docNameField)) {
                    return Status.YES;
                } else {
                    return Status.NO;
                }
            }
        });
        if (name.size() != 0) {
            return name.get(0);
        } else {
            return null;
        }
    }

}