BeanShell promises lightweight scripting for Java. Support for BeanShell is included with the Apache ant build tool, and it is targetted to be included as a part of the standard edition of Java with JSR-274. I’ve recently included BeanShell in a project, and will share what I have achieved with this, and some of the motivations and considerations when doing this.

My primary reason for adding BeanShell was that we use some heavy enterprise APIs. We are able to mock these out for development, but have experienced consistent issues when working with the APIs, primarily caused by missing or misleading documentation. This means that there is often a need to write code to understand the APIs. To deploy to the application server takes about 3 minutes, and the wrestling required to make the code work is often much more painful that expected. It is pain which motivates the creation of some nice tools, and this pain motivated the creation of a simple tool using BeanShell.

In it’s simplest form, the tool allows the execution of code on the server that has been input into a text area. This is a powerful tool for developers and admins, but is somewhat (ok very) risky from a security standpoint, and needs to be treated as such.  Getting BeanShell up and running is really straightforward.  I've only got a couple of recommendations and comments to make about doing so.

1. Integrating BeanShell itself is really straightforward. Simply have a servlet (action/jsp/whatever) which reads in a request parameter, uses an instance of the beanshell interpreter class to eval the string. The quickstart guide makes it clear and easy to get started (makes it quick to start ).
2. In order to make the interpreter useful, you will want to have add imports of the important packages for your application (such as to your Data Access Layer), and also the set some variables on the context. Prepend the imports to the scripts before they are eval'ed, and set the variables using the interpreter set(String, Object) method.
3. In addition to the result of the script, and the application variables that I put on the interpreter, I also add in a PrintStream, making it easy to output debug information.
4. Finally, it is really useful to keep track of what statements have been executed, and the results of the statements.  Save these to the session, and list these on the page. A simple javascript function makes it possible to replace the contents of the text area with previous scripts, and also the output, and result messages.  This rounds out a simple little tool nicely.1

By doing this, it is possible to explore APIs, and work at a very quick pace. Whenever something behaves unexpectedly on the server, one can quickly explore what has happened, and produce the updates to production code, which are required to make this work. BeanShell is a powerful tool for serverside development, and well worth considering adding to your toolkit.

1 - for extra credit, it is really easy to keep a list of previous statements on the page, and use the javascript above to keep track of the history.↩

This entry was posted on Monday, May 12th, 2008 at 3:32 am and is filed under Development, Java. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.