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I work with Mule on a regular basis and am used to the error messages that may sometimes seem cryptic to the untrained eye. The truth is that they are not cryptic at all, if you know what to look for.

Nowadays, I tend to look at an error and can diagnose common or familiar ones with ease. Beginners may not realise how I manage to do this so this post is the first in a series of posts that explains why a seemingly baffling error message can be resolved in a matter of minutes.

Take a look at this extract from a log4j file (or console)

ERROR [main] org.mule.config.spring.SpringXmlConfigurationBuilder:
Configuration with "org.mule.config.spring.
SpringXmlConfigurationBuilder" failed.
org.mule.api.lifecycle.InitialisationException: Initialisation
Failure: Error creating bean with name 'jmsConnector': Invocation
of init method failed; nested exception is
org.mule.api.MuleRuntimeException: Exception occurred
on connector "jmsConnector". Exception listener is not set. This
could result in message loss
 	at org.mule.registry.AbstractRegistry.initialise
 	at ...

This error occurs when you try to start up a Mule server. It is raised from within the SpringXmlConfigurationBuilder which means that the configuration file is being parsed/used, i.e., before the Mule server is completely initialised.

We can tell that the item called jmsConnector cannot be created and so this is where the problem is. If the problem was with any of the configured values, the error message will continue to talk about this. In my case, the relevant configuration looks like this:

Nothing wrong there, so the problem must be elsewhere.

A close look at the error message indicates that the problem is something to do with the ExceptionListener which could not be set. As you can see from the configuration, I am not explicitly configuring an exception strategy so this is not a configuration related error.

I know that I have declared the namespace and schemas in my configuration file. If I had not done this, the XML would not have been parsed properly (Note that I use the jms prefix in the configuration) so this cannot be it either.

Last stop is to double check that I have included the mule-transport-jms JAR in my project. This can vary depending on whether I’m using something like Maven or Ant, including JARs in my project (in Eclipse) or including source projects if I have access to the code base. Don’t forget to make sure that Mule can access this JAR at runtime.

This last step fixed the problem.

Moral of this post: While the error seemed to suggest something related to exception handling, look at the entire error message for hidden clues and tips.