topic Re: Intermittent issues with JuelExpression in Alfresco Archive

Intermittent issues with JuelExpression

hburgett — Mon, 24 Oct 2011 16:50:17 GMT

Hi,I have been getting intermittent exceptions from the Activiti Engine that look like the following (complete stack trace shortened for brevity)rg.activiti.engine.ActivitiException: Error while evalutaing expression at org.activiti.engine.impl.el.JuelExpression.getValue(JuelExpression.java:52)

Re: Intermittent issues with JuelExpression

hburgett — Mon, 24 Oct 2011 21:18:25 GMT

I am running this in a web app (WAR) using JBoss AS 5.1. I noticed that JBoss comes with a el-api.jar containing classes like javax.el.ExpressionFactory. Could this some strange classloader issue?

Re: Intermittent issues with JuelExpression

hburgett — Thu, 03 Nov 2011 18:11:34 GMT

Solution:

JBoss AS 5.1 executes the JMS onMessage() operation using the classloader of the message sender, not the web context classloader of the receiver. This results in the exception above because the org.activiti.engine.impl.javax.el.ExpressionFactory.newInstance() method does a type check using Class.isAssignableFrom(), and the 2 types it is comparing come from 2 different class loaders, so the comparison fails.

Bottom Line: make sure the classloader used to execute Activiti inside a JBoss WAR does not get switched when responding to JMS messages.

My workaround was to assign the classloader manually in my JMS listener:


    @Override
    public void onMessage(Message msg)
    {
        if (msg instanceof TextMessage)
        {
            ClassLoader originalCL = Thread.currentThread().getContextClassLoader();
            
            try
            {
                String xml = ((TextMessage) msg).getText();

                Thread.currentThread().setContextClassLoader( this.getClass().getClassLoader() );

                 doActivitiStuff();

            }
            catch (JMSException e)
            {
                e.printStackTrace();
            }
            finally
            {
                Thread.currentThread().setContextClassLoader( originalCL );
            }
        }
    }

Re: Intermittent issues with JuelExpression

trademak — Fri, 04 Nov 2011 09:34:38 GMT

I would recommend to take a look at the camunda fox platform, which provides native integration of the Activiti Engine in JBoss.

Best regards,