gwt + java rule engine

would like to provide customers with the ability to create a rule and have it evaluated on the back end and when rule conditions are true, customer would either receive and email, sms, or twitter like page update. If programmer can handle web interface great, but my main concern is the back end. What I have now is as follows: data is generated and published to an activemq topic. Global variables that customer rules would run against are stored in memcached.. I can create standalone java clients that consume the activemq topic of data and compare to variables stored in memecahced using conditional statements, then publish to another queue or topic the result if true. Where I need help is creating a modular system so that my cusomters can create a rule, which will then somehow be imported and then the code generated and loaded dynamically. I realize that the rule generation will be a little tricky. However the rules will be fairly simple. Mostly if then, perhaps with some nested if then statements. I was thinking of having a web interface generate JSON strings for each condition. You must somehow take the json strings (or best approach) and generate the java code (i will keep this part simple, again just very simple conditional statements), then have that module consume the activemq datafeed, execute the statements then publish back the output. Runs on fedora linux. I hope that was not too confusing