com.b2international.index.lucene.NullIndexSearcher.java Source code

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Here is the source code for com.b2international.index.lucene.NullIndexSearcher.java

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/*
 * Copyright 2011-2016 B2i Healthcare Pte Ltd, http://b2i.sg
 * 
 * Licensed 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 com.b2international.index.lucene;

import java.io.IOException;

import org.apache.lucene.analysis.core.WhitespaceAnalyzer;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.IndexWriterConfig;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.store.RAMDirectory;

/**
 * Null implementation of an {@link IndexSearcher index searcher}.
 */
public class NullIndexSearcher extends IndexSearcher {

    /**Shared NULL instance.*/
    private static IndexSearcher instance;

    /**Returns with the shared {@link #instance NULL} instance.*/
    public static IndexSearcher getInstance() {

        if (null == instance) {

            synchronized (NullIndexSearcher.class) {

                if (null == instance) {

                    try {

                        instance = new NullIndexSearcher();

                    } catch (final IOException e) {

                        throw new RuntimeException("Error while instantiating NULL index searcher.", e);

                    }

                }

            }

        }

        return instance;

    }

    /*Private constructor wrapping an empty RAM directory.*/
    private NullIndexSearcher() throws IOException {
        super(createRamReader());
    }

    /*creates a reader backed with a RAM directory*/
    private static DirectoryReader createRamReader() throws IOException {

        final RAMDirectory directory = new RAMDirectory();
        if (!DirectoryReader.indexExists(directory)) {

            final IndexWriterConfig conf = new IndexWriterConfig(new WhitespaceAnalyzer());
            final IndexWriter writer = new IndexWriter(directory, conf);
            writer.commit();
            writer.close();
        }

        return DirectoryReader.open(directory);

    }

}