1   /**
    2    * Licensed under the Artistic License; you may not use this file
    3    * except in compliance with the License.
    4    * You may obtain a copy of the License at
    5    *
    6    *      http://displaytag.sourceforge.net/license.html
    7    *
    8    * THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
    9    * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
   10    * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
   11    */
   12   package org.displaytag.util;
   13   
   14   import javax.servlet.jsp.JspTagException;
   15   
   16   import org.displaytag.Messages;
   17   
   18   
   19   /**
   20    * An user-friendly dependency checker. This will check the presence of libraries needed by displaytag, throwing an
   21    * Exception with an informative message if the library is missing or the version is not compatible.
   22    * @author Fabrizio Giustina
   23    * @version $Revision: 1081 $ ($Author: fgiust $)
   24    */
   25   public final class DependencyChecker
   26   {
   27   
   28       /**
   29        * Has the commons-lang dependency been checked?
   30        */
   31       private static boolean commonsLangChecked;
   32   
   33       /**
   34        * Don't instantiate.
   35        */
   36       private DependencyChecker()
   37       {
   38           // unused
   39       }
   40   
   41       /**
   42        * Displaytag requires commons-lang 2.x or better; it is not compatible with earlier versions.
   43        * @throws JspTagException if the wrong library, or no library at all, is found.
   44        */
   45       public static void check() throws JspTagException
   46       {
   47           if (commonsLangChecked)
   48           {
   49               return;
   50           }
   51           try
   52           {
   53               // Do they have commons lang ?
   54               Class stringUtils = Class.forName("org.apache.commons.lang.StringUtils"); //$NON-NLS-1$
   55               try
   56               {
   57                   // this method is new in commons-lang 2.1
   58                   stringUtils.getMethod("splitPreserveAllTokens", new Class[]{String.class}); //$NON-NLS-1$
   59               }
   60               catch (NoSuchMethodException ee)
   61               {
   62                   throw new JspTagException(Messages.getString("DependencyChecker.lib.incompatible", //$NON-NLS-1$
   63                       new Object[]{"commons-lang", "2.1", "http://jakarta.apache.org/commons/lang"} //$NON-NLS-1$ //$NON-NLS-1$
   64                       ));
   65               }
   66           }
   67           catch (ClassNotFoundException e)
   68           {
   69               throw new JspTagException(Messages.getString("DependencyChecker.lib.missing", //$NON-NLS-1$
   70                   new Object[]{"commons-lang", "2.1", "http://jakarta.apache.org/commons/lang"} //$NON-NLS-1$ //$NON-NLS-1$
   71                   ));
   72           }
   73           commonsLangChecked = true;
   74       }
   75   
   76   }