/** * Licensed under the Artistic License; you may not use this file * except in compliance with the License. * You may obtain a copy of the License at * *      http://displaytag.sourceforge.net/license.html * * THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. */package org.displaytag.util;import javax.servlet.jsp.JspTagException;import org.displaytag.Messages;/** * An user-friendly dependency checker. This will check the presence of libraries needed by displaytag, throwing an * Exception with an informative message if the library is missing or the version is not compatible. * @author Fabrizio Giustina * @version $Revision: 1081 $ ($Author: fgiust $) */public final class DependencyChecker{    /**     * Has the commons-lang dependency been checked?     */    private static boolean commonsLangChecked;    /**     * Don't instantiate.     */    private DependencyChecker()    {        // unused    }    /**     * Displaytag requires commons-lang 2.x or better; it is not compatible with earlier versions.     * @throws JspTagException if the wrong library, or no library at all, is found.     */    public static void check() throws JspTagException    {        if (commonsLangChecked)        {            return;        }        try        {            // Do they have commons lang ?            Class stringUtils = Class.forName("org.apache.commons.lang.StringUtils"); //$NON-NLS-1$            try            {                // this method is new in commons-lang 2.1                stringUtils.getMethod("splitPreserveAllTokens", new Class[]{String.class}); //$NON-NLS-1$            }            catch (NoSuchMethodException ee)            {                throw new JspTagException(Messages.getString("DependencyChecker.lib.incompatible", //$NON-NLS-1$                    new Object[]{"commons-lang", "2.1", "http://jakarta.apache.org/commons/lang"} //$NON-NLS-1$ //$NON-NLS-1$                    ));            }        }        catch (ClassNotFoundException e)        {            throw new JspTagException(Messages.getString("DependencyChecker.lib.missing", //$NON-NLS-1$                new Object[]{"commons-lang", "2.1", "http://jakarta.apache.org/commons/lang"} //$NON-NLS-1$ //$NON-NLS-1$                ));        }        commonsLangChecked = true;    }}