net.sf.logsaw.index.internal.ARunWithIndexReader.java Source code

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Here is the source code for net.sf.logsaw.index.internal.ARunWithIndexReader.java

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/*******************************************************************************
 * Copyright (c) 2010, 2011 LogSaw project and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    LogSaw project committers - initial API and implementation
 *******************************************************************************/
package net.sf.logsaw.index.internal;

import java.io.IOException;

import net.sf.logsaw.core.logresource.ILogResource;
import net.sf.logsaw.index.IndexPlugin;

import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.core.runtime.Status;
import org.eclipse.osgi.util.NLS;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * This is a convenience base class for executing code which requires an <code>IndexReader</code>.
 * 
 * @author Philipp Nanz
 * @param <T> the return type
 */
public abstract class ARunWithIndexReader<T> {

    private static transient Logger logger = LoggerFactory.getLogger(ARunWithIndexReader.class);

    private LuceneQueryContextImpl queryContext;

    /**
     * Obtains a index reader from the query context or opens a new one.
     * @param log the log resource
     * @return a new index reader or <code>null</code>
     * @throws IOException if an error occurred
     */
    protected IndexReader getFromQueryContextOrOpenIndexReader(ILogResource log) throws IOException {
        IndexReader reader = null;
        if (queryContext != null) {
            reader = queryContext.getIndexReader();
            if (reader == null) {
                reader = openReader(log);
                logger.info("Binding index reader to query context " + queryContext.toString()); //$NON-NLS-1$
                queryContext.setIndexReader(reader);
            }
            return reader;
        }
        return openReader(log);
    }

    /**
     * Opens a fresh index reader.
     * @param log the log resource
     * @return a new index reader or <code>null</code>
     * @throws IOException if an error occurred
     */
    protected IndexReader openReader(ILogResource log) throws IOException {
        IndexReader reader = null;
        Directory dir = FSDirectory.open(IndexPlugin.getDefault().getIndexFile(log));
        if (DirectoryReader.indexExists(dir)) {
            logger.info("Opening index reader for '" + log.getName() + "'..."); //$NON-NLS-1$ //$NON-NLS-2$
            reader = DirectoryReader.open(dir);
        }
        return reader;
    }

    /**
     * @param queryContext the queryContext to set
     */
    protected void setQueryContext(LuceneQueryContextImpl queryContext) {
        this.queryContext = queryContext;
    }

    /**
     * Opens a Lucene index reader, executes the callback method and then closes the reader.
     * @param log the log resource, may be <code>null</code>
     * @return any object or <code>null</code>
     * @throws CoreException if an <strong>expected</strong> error occurred
     */
    protected final T runWithIndexReader(ILogResource log) throws CoreException {
        IndexReader reader = null;
        try {
            reader = getFromQueryContextOrOpenIndexReader(log);
            try {
                return doRunWithIndexReader(reader, log);
            } finally {
                if ((queryContext == null) && (reader != null)) {
                    // Close only if not in session
                    logger.info("Closing index reader for '" + log.getName() + "'..."); //$NON-NLS-1$ //$NON-NLS-2$
                    reader.close();
                }
            }
        } catch (CoreException e) {
            // Rethrow original CoreException
            throw e;
        } catch (Exception e) {
            // Unexpected exception; wrap with CoreException
            throw new CoreException(new Status(IStatus.ERROR, IndexPlugin.PLUGIN_ID,
                    NLS.bind(Messages.LuceneIndexService_error_failedToReadIndex,
                            new Object[] { log.getName(), e.getLocalizedMessage() }),
                    e));
        }
    }

    /**
     * Callback method being called by <code>runWithIndexReader(ILogResource, ILogDialect)</code>.
     * @param reader the index reader, may be <code>null</code> to indicate that index does not exist yet
     * @param log the log resource, may be <code>null</code>
     * @return any object or <code>null</code>
     * @throws CoreException if an <strong>expected</strong> error occurred
     */
    protected abstract T doRunWithIndexReader(IndexReader reader, ILogResource log) throws CoreException;

}