It is possible to fully integrate the Atomikos transaction manager into Tomcat. Doing it this way makes the transaction manager shared across all web applications exactly like with any full-blown J2EE server.

Important note

When the Atomikos transaction manager is installed globally in Tomcat, you now must also install your JDBC driver at the same global location (ie: into the TOMCAT_HOME/common/lib folder). If you dont do that, you will get a NoClassDefFoundErrors or a ClassNotFoundException or even a ClassCastException during your web application deployment.

This is not a limitation of Atomikos nor of Tomcat but of the J2EE class loading design that both Tomcat and Atomikos must follow.

Installation

Installation is quite simple, it just involves copying some JAR files, a propery file and editing some Tomcat configuration files.

Copying Atomikos Tomcat Lifecycle library

• Drop this JAR file into the TOMCAT_HOME/server/lib folder: atomikos-tomcat-lifecycle.jar

This JAR contains a single class file that is a Tomcat lifecycle lsitener: it listens for Tomcat's startup and shutdown events and start or stop the transaction manager accordingly. Here is its source code:

Atomikos Lifecycle Listener.java

package com.atomikos.tomcat;

import org.apache.catalina.Lifecycle;
import org.apache.catalina.LifecycleEvent;
import org.apache.catalina.LifecycleListener;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.atomikos.icatch.jta.UserTransactionManager;
import com.atomikos.icatch.system.Configuration;

public class AtomikosLifecycleListener implements LifecycleListener {

   private static Log log = LogFactory.getLog(AtomikosLifecycleListener.class);

   private UserTransactionManager utm;

   public void lifecycleEvent(LifecycleEvent event) {
      if (Lifecycle.START_EVENT.equals(event.getType())) {
         if (utm == null) {
            log.info("starting Atomikos Transaction Manager " + Configuration.VERSION);
            utm = new UserTransactionManager();
         }
      }
      else if (Lifecycle.STOP_EVENT.equals(event.getType())) {
         if (utm != null) {
            log.info("shutting down Atomikos Transaction Manager");
            utm.close();
         }
      }
   }

}

Copying TransactionsEssentials libraries

• Drop the following JARs from the Atomikos distribution into the TOMCAT_HOME/common/libfolder:
  • transactions.jar
  • transactions-api.jar
  • transactions-jta.jar
  • atomikos-util.jar.jar
  • jta.jar

You should also copy the transactions-hibernate3.jar and/or transactions-hibernate2.jar at the same location if you're planning to use Hibernate.

Copying Atomikos configuration file

• Drop the following properties file into the TOMCAT_HOME/common/classes folder: jta.properties

Edit server.xml

Then edit the TOMCAT_HOME/conf/server.xml file. At the beginning of the file you should see these four lines:

  <Listener className="org.apache.catalina.core.AprLifecycleListener" />
  <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" />
  <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />
  <Listener className="org.apache.catalina.storeconfig.StoreConfigLifecycleListener"/>

Right after the last one, add this fifth one:

 <Listener className="com.atomikos.tomcat.AtomikosLifecycleListener" />

Edit context.xml

Then edit the TOMCAT_HOME/conf/context.xml file. At the beginning of the file you should see this line:

 <WatchedResource>WEB-INF/web.xml</WatchedResource>

Right after it, add that one:

 <Transaction factory="com.atomikos.icatch.jta.UserTransactionFactory" />

Example application

Here is a sample application that demonstrates how you can run TransactionsEssentials in a web application after it has been globally installed.

It is a simple blueprint application that shows and updates the content of a single Derby database.

Download the sample application here: dbtest.war

To install it, simply copy the WAR file in Tomcat's webapps folder. You also need to install Derby's JDBC driver in TOMCAT_HOME/common/lib.

You can then access it via this URL: http://localhost:8080/dbtest/.

Notes

• This demo uses an embedded Derby database. If it doesn't exist a new one is created in TOMCAT_HOME/work or else, the existing one is reused.
• The transactions logs and debug logs are stored in TOMCAT_HOME/work.
• You should get logs during Tomcat's startup and shutdown:
  • during startup: INFO: starting Atomikos Transaction Manager 3.2.2
  • during shutdown: INFO: shutting down Atomikos Transaction Manager