source: main/trunk/greenstone3/src/java/org/greenstone/gsdl3/util/JDBMWrapper.java@ 30264

/*
 *    JDBMWrapper.java
 *    Copyright (C) 2008 New Zealand Digital Library, http://www.nzdl.org
 *
 *    This program is free software; you can redistribute it and/or modify
 *    it under the terms of the GNU General Public License as published by
 *    the Free Software Foundation; either version 2 of the License, or
 *    (at your option) any later version.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU General Public License for more details.
 *
 *    You should have received a copy of the GNU General Public License
 *    along with this program; if not, write to the Free Software
 *    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
package org.greenstone.gsdl3.util;

import org.apache.log4j.Logger;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

import java.util.Properties;
import java.util.ArrayList;

import jdbm.RecordManager;
import jdbm.RecordManagerFactory;
import jdbm.helper.FastIterator;
import jdbm.htree.HTree;

public class JDBMWrapper implements FlatDatabaseWrapper
{

    static Logger logger = Logger.getLogger(org.greenstone.gsdl3.util.JDBMWrapper.class.getName());

    static String TNAME = "greenstone";

    RecordManager recman_ = null;
    HTree hashtable_;

    String db_filename_;

    static private PrintWriter utf8out = null;

    static
    {
        try
        {
            OutputStreamWriter osw = new OutputStreamWriter(System.out, "UTF-8");
            utf8out = new PrintWriter(osw, true);
        }
        catch (UnsupportedEncodingException e)
        {
            System.out.println(e);
        }
        // Register this wrapper with DBHelper
        DBHelper.registerDBTypeExt("jdbm",".jdb");
    }

    /** open database named filename, using mode */
    public boolean openDatabase(String db_filename, int mode)
    {
            String db_filename_with_ext = db_filename;

        if (db_filename.endsWith(".jdb"))
        {
            // remove file extension as JDBM does not expect it
            db_filename = db_filename.substring(0, db_filename.length() - 4);
        }

        // Map the mode value into equivalent JDBM 'must_exist' value
        // currently this is very simple as there is only READ and WRITE
        // (no WRITER_CREATE)
        // => assume the database must exist
        boolean must_exist = true; // default

        if (recman_ != null)
        {
            String message = "openDatabase() called when the class already has a database open\n";
            message += "  Use closeDatabase before opening the next one.\n";
            message += "  Existing database file: " + db_filename_ + "\n";
            message += "  New database file:      " + db_filename + "\n";
            logger.warn(message);
            // consider closing it automatically?
        }

        try
        {
            // create or open a record manager
            Properties props = new Properties();
            recman_ = RecordManagerFactory.createRecordManager(db_filename, props);
            
            // load existing table (if exists) otherwise create new one
            long recid = recman_.getNamedObject(TNAME);

            if (recid != 0)
            {
                logger.info("# Loading existing database table '" + TNAME + "' ...");
                hashtable_ = HTree.load(recman_, recid);
            }
            else
            {
                if (must_exist)
                {
                    recman_.close();
                    recman_ = null;
                    db_filename_ = null;

                    logger.error("Database table '" + TNAME + "' does not exist.");
                    throw new IOException();
                }
                else
                {
                    logger.info("# No database table '" + TNAME + "' to set.  Creating new one");
                    hashtable_ = HTree.createInstance(recman_);
                    recman_.setNamedObject(TNAME, hashtable_.getRecid());
                }
            }
        }
        catch (IOException e)
        {
            e.printStackTrace();

            logger.error("couldn't open database " + db_filename_with_ext);
            return false;
        }

        db_filename_ = db_filename;

        return true;
    }

    /** close the database associated with this wrapper */
    public void closeDatabase()
    {
        try
        {
            if (recman_ != null)
            {
                recman_.close();
                recman_ = null;
                db_filename_ = null;
            }
        }
        catch (IOException e)
        {
            logger.error("Failed to close JDBM database");
        }
    }

    /** returns the value associated with the key */
    public String getValue(String key)
    {

        String val;

        try
        {
            val = (String) hashtable_.get(key);
            
            recman_.commit();
        }
        catch (IOException e)
        {
            logger.error("Failed get key " + key + "from JDBM database");
            return null;
        }
        
        return val;
    }
    
    /**
     * Sets the given key to the given value in the database
     */
    public boolean setValue(String key, String value)
    {
        try
        {
            hashtable_.put(key, value);
            recman_.commit();
        }
        catch (Exception ex)
        {
            logger.error("Failed to set " + key + " = " + value + " in the JDBM database");
            return false;
        }
        return true;
    }

    /**
     * Deletes the given key (and corresponding value) from the database
     */
    public boolean deleteKey(String key)
    {
        try
        {
            hashtable_.remove(key);
            recman_.commit();
        }
        catch (Exception ex)
        {
            logger.error("Failed to delete key " + key + " in the JDBM database");
            return false;
        }
        return true;
    }

    /**
     * returns a string of key-value entries that can be printed for debugging
     * purposes
     */
    public String displayAllEntries()
    {

        StringBuffer keys = new StringBuffer();

        try
        {
            FastIterator iter = hashtable_.keys();
            String key = (String) iter.next();

            String nl = System.getProperty("line.separator");

            while (key != null)
            {
                String val = (String) hashtable_.get(key);
                keys.append("[" + key + "]" + nl);
                keys.append(val + nl);
                // 70 hypens
                keys.append("----------------------------------------------------------------------" + nl);
                key = (String) iter.next();
            }

            recman_.commit();
        }
        catch (IOException e)
        {
            logger.error("Failed get all keys and values from JDBM database");
            return null;
        }

        return keys.toString();
    }
}