BeanShell is a small, free, embeddable Java source interpreter with object scripting language features, written in Java. BeanShell dynamically executes standard Java syntax and extends it with common scripting conveniences such as loose types, commands, and method closures like those in Perl and JavaScript.

Homepage: http://www.beanshell.org .

You can hot deploy BeanShell scripts in JBoss using the BSHDeployer.

Instructions for upgrading BeanShell can be found here.