/*
 * Copyright (c) 2010 by Intevation GmbH
 *
 * This program is free software under the LGPL (>=v2.1)
 * Read the file LGPL.txt coming with the software for details
 * or visit http://www.gnu.org/licenses/ if it does not exist.
 */

package de.intevation.artifactdatabase;

import java.io.File;

import java.sql.SQLException;

import javax.sql.DataSource;

import org.apache.commons.dbcp.BasicDataSource;

import org.apache.log4j.Logger;

/**
 * This class encapsulate the creation and pooling of database connections used
 * by the artifact database. The credential to open the database connections
 * are taken from the global configuratiion.
 * @author <a href="mailto:sascha.teichmann@intevation.de">Sascha L. Teichmann</a>
 */
public class DBConnection
{
    private static Logger logger = Logger.getLogger(DBConnection.class);

    /**
     * XPath to access the database driver within the global configuration.
     */
    public static final String DB_DRIVER =
        "/artifact-database/database/driver/text()";
    /**
     * XPath to access the database URL within the global configuration.
     */
    public static final String DB_URL =
        "/artifact-database/database/url/text()";
    /**
     * XPath to access the database use within the global configuration.
     */
    public static final String DB_USER =
        "/artifact-database/database/user/text()";
    /**
     * XPath to access the database password within the global configuration.
     */
    public static final String DB_PASSWORD =
        "/artifact-database/database/password/text()";

    /**
     * The default database driver: H2
     */
    public static final String DEFAULT_DRIVER =
        "org.h2.Driver";

    /**
     * The default database name: artifacts.db
     */
    public static final String DEFAULT_DATABASE_FILE =
        "artifacts.db";

    /**
     * The default database URL: This is created once by #getDefaultURL()
     */
    public static final String DEFAULT_URL = getDefaultURL();

    /**
     * The default database user: ""
     */
    public static final String DEFAULT_USER     = "";

    /**
     * The default database password: ""
     */
    public static final String DEFAULT_PASSWORD = "";

    private DBConnection() {
    }

    /**
     * Constructs the default databse URL. It concats the
     * config directory and the #DEFAULT_DATABASE_FILE
     * to the string with is needed to access H2 databases.
     * @return The default URL.
     */
    public static final String getDefaultURL() {
        File configDir = Config.getConfigDirectory();
        File databaseFile = new File(configDir, DEFAULT_DATABASE_FILE);
        return "jdbc:h2:" + databaseFile;
    }

    private static BasicDataSource dataSource;

    private static final void addShutdownHook() {
        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                if (dataSource != null) {
                    try {
                        dataSource.close();
                    }
                    catch (SQLException sqle) {
                    }
                    dataSource = null;
                }
            }
        });
    }

    /**
     * Static method to fetch a database connection.
     * @return a DataSource to access the database connection.
     */
    public static synchronized DataSource getDataSource() {
        if (dataSource == null) {
            dataSource = new BasicDataSource();

            String driver = Config.getStringXPath(
                DB_DRIVER, DEFAULT_DRIVER);

            String url = Config.getStringXPath(
                DB_URL, DEFAULT_URL);

            url = Config.replaceConfigDir(url);

            String user = Config.getStringXPath(
                DB_USER, DEFAULT_USER);

            String password = Config.getStringXPath(
                DB_PASSWORD, DEFAULT_PASSWORD);

            logger.info("database driver: " + driver);
            logger.info("database url: " + url);

            dataSource.setDriverClassName(driver);
            dataSource.setUsername(user);
            dataSource.setPassword(password);
            dataSource.setUrl(url);
            addShutdownHook();
        }

        return dataSource;
    }
}
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