jelly-tags/jms/src/java/org/apache/commons/jelly/tags/jms/OnMessageTag.java

/*
 * Copyright 2002,2004 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.jelly.tags.jms;

import javax.jms.Message;
import javax.jms.MessageListener;

import org.apache.commons.jelly.JellyContext;
import org.apache.commons.jelly.JellyTagException;
import org.apache.commons.jelly.Script;
import org.apache.commons.jelly.TagSupport;
import org.apache.commons.jelly.XMLOutput;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * This tag creates a JMS MessageListener which will invoke this
 * tag's body whenever a JMS Message is received. The JMS Message
 * will be available via a variable, which defaults to the 'message'
 * variable name, but can be overloaded by the var attribute.
 *
 * @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
 * @version $Revision: 1.6 $
 */
public class OnMessageTag extends TagSupport {

    /** The Log to which logging calls will be made. */
    private static final Log log = LogFactory.getLog(OnMessageTag.class);

    private String var = "message";

    public OnMessageTag() {
    }

    // Tag interface
    //-------------------------------------------------------------------------
    public void doTag(XMLOutput output) throws JellyTagException {
        ConsumerTag tag = (ConsumerTag) findAncestorWithClass(ConsumerTag.class);
        if (tag == null) {
            throw new JellyTagException("This tag must be nested within a ConsumerTag like the subscribe tag");
        }

        final JellyContext childContext = context.newJellyContext();
        final Script script = getBody();
        final XMLOutput childOutput = output;

        MessageListener listener = new MessageListener() {
            public void onMessage(Message message) {
                childContext.setVariable(var, message);
                try {
                    script.run(childContext, childOutput);
                }
                catch (Exception e) {
                    log.error("Caught exception processing message: " + message + ". Exception: " + e, e);
                }
            }
        };

        // perform the consumption
        tag.setMessageListener(listener);
    }


    // Properties
    //-------------------------------------------------------------------------

    /**
     * Sets the name of the variable used to make the JMS message available to this tags
     * body when a message is received.
     */
    public void setVar(String var) {
        this.var = var;
    }
}