Check for resource/configuration existence [WLST scripting Best Practices (Part-3)]

This post is a continuation of my previous post in a series of posts about WLST scripting best practices. When you are authoring WLST scripts to create new resource/configuration in WebLogic domain then check for its existence. If the resource/configuration already exists then you might get an error similar to the following:

weblogic.descriptor.BeanAlreadyExistsException: Bean already exists

A simple approach is to use the "cd" command to navigate into that configuration MBean. If the "cd" command throws an exception then you can safely assume that the resource/configuration doesn't exists and you can continue creating.

...
### Check for the server
try: 
    cd('/Servers/' + mgdServerName)
    print '===> Server \"' +mgdServerName+'\" already exists'
    print '===> No action was performed'
    exit()
except:
    pass
...

The other approach is to catch the "BeanAlreadyExistsException" while creating the resource and safely exiting the script.

...
### Create the Managed Server
edit()
startEdit()
try:
    create(mgdServerName, resourceType)
    print '===> Created Managed Server - ' + mgdServerName
    pass 
except BeanAlreadyExistsException:
    print '===> Server \"' +mgdServerName+'\" already exists'
    print '===> No action was performed'
    cancelEdit('y')
    exit()
...

But with this approach you are starting an edit session and creating the server to find out it's existence. So you have to cancel the edit session once you find out that the resource that you are creating already exists if not you might get a warning message similar to the following:

You have an edit session open and you will lose all outstanding changes and your edit session will be stopped if you exit. Are you sure you would like to exit? (y/n)

So cancelling the edit session with a responce 'y' will make WLST not to prompt for user response. I shall discuss how to streamline the outputs from WLST and redirect them to an output file or log file in a later post.

WLST-BP-3 Check for the resource or configuration existence before creating them