TryCatchDirective

TryCatchDirective.java

/*
 * See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */
package org.xwiki.velocity.introspection;

import java.io.IOException;
import java.io.Writer;

import org.apache.velocity.context.InternalContextAdapter;
import org.apache.velocity.exception.MethodInvocationException;
import org.apache.velocity.exception.ParseErrorException;
import org.apache.velocity.exception.ResourceNotFoundException;
import org.apache.velocity.exception.VelocityException;
import org.apache.velocity.runtime.directive.Directive;
import org.apache.velocity.runtime.parser.node.Node;

/**
 * Allows catching exception from Velocity. Example usage:
 * <pre>
 * {@code #try()
 *   ...
 *   #end
 *
 *   ## At this stage $exception contains the exception if any has been thrown.
 *   ## It can be tested like this:
 *   #if ("$!exception" != '')
 *     ## An exception has been thrown
 *   #end}
 * </pre>
 *
 * @version $Id: 432f8b6d2499c490e6995f2b7f27067dd58537c9 $
 * @since 6.3M1
 */
public class TryCatchDirective extends Directive
{
    static final String IN_TRY_DIRECTIVE_KEY_NAME = "insidevelocitytrydirective";

    private static final String EXCEPTION_KEY_NAME = "exception";

    @Override
    public String getName()
    {
        return "try";
    }

    @Override
    public int getType()
    {
        return BLOCK;
    }

    @Override
    public boolean render(InternalContextAdapter context, Writer writer, Node node)
        throws IOException, ResourceNotFoundException, ParseErrorException, MethodInvocationException
    {
        try {
            // Make sure to clear any previous exception
            context.remove(EXCEPTION_KEY_NAME);
            // Set that we're inside a try directive. This is used by the ExceptionCatchingUberspector (for ex).
            context.put(IN_TRY_DIRECTIVE_KEY_NAME, true);
            return node.jjtGetChild(0).render(context, writer);
        } catch (Exception e) {
            // Since the Exception could have been caught and rethrown by the Exception Catching Uberspector and since
            // in that case the Velocity runtime will wrap it in a VelocityException exception, we need to unwrap it...
            Exception originalException = e;
            if (originalException instanceof VelocityException) {
                Throwable originalThrowable = ((VelocityException) e).getWrappedThrowable();
                if (originalThrowable instanceof Exception) {
                    originalException = (Exception) originalThrowable;
                }
            }
            // Save the exception in the $exception velocity context variable
            context.put(EXCEPTION_KEY_NAME, originalException);
            return true;
        } finally {
            // Remove the fact that we're inside a try directive
            context.remove(IN_TRY_DIRECTIVE_KEY_NAME);
        }
    }
}