net.conquiris.search.EmptyIndex.java Source code

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Here is the source code for net.conquiris.search.EmptyIndex.java

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/*
 * Copyright (C) the original author or authors.
 *
 * 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 net.conquiris.search;

import java.io.IOException;
import java.lang.ref.WeakReference;

import net.conquiris.api.search.IndexNotAvailableException;
import net.conquiris.api.search.Reader;
import net.conquiris.lucene.Conquiris;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.RAMDirectory;

/**
 * Empty RAM-based index.
 * @author Andres Rodriguez
 */
final class EmptyIndex extends AbstractReaderSupplier {
    /** Instance. */
    private static volatile WeakReference<EmptyIndex> instance;

    /** Returns the shared instance. */
    static EmptyIndex getInstance() {
        try {
            final WeakReference<EmptyIndex> r = instance;
            if (r != null) {
                EmptyIndex i = r.get();
                if (i != null) {
                    return i;
                }
            }
            return create();
        } catch (IOException e) {
            // Should not happen.
            throw new IndexNotAvailableException(e);
        }
    }

    /** Returns a new initalized RAM-based empty directory. */
    static Directory newDirectory() {
        try {
            return new EmptyIndex().directory;
        } catch (IOException e) {
            // Should not happen.
            throw new IndexNotAvailableException(e);
        }
    }

    private static synchronized EmptyIndex create() throws IOException {
        if (instance != null) {
            EmptyIndex i = instance.get();
            if (i != null) {
                return i;
            }
        }
        EmptyIndex i = new EmptyIndex();
        instance = new WeakReference<EmptyIndex>(i);
        return i;
    }

    /** Directory. */
    private final Directory directory;

    /** Constructor. */
    private EmptyIndex() throws IOException {
        this.directory = new RAMDirectory();
        IndexWriter w = new IndexWriter(directory, Conquiris.writerConfig());
        w.close();
    }

    /*
     * (non-Javadoc)
     * @see net.conquiris.search.AbstractReaderSupplier#doGet()
     */
    @Override
    Reader doGet() throws IOException {
        return Reader.of(IndexReader.open(getInstance().directory), false);
    }

}