The following example of using Groovy to execute arbitrary code in a running web application is excerpted from a longer article originally posted to Bruce Fancher's blog. The code and examples can be downloaded from here.
In order to add the GroovyServer to the application, I added the following lines to the Spring appContext.xml file:
You'll note that there are actually two Groovy-related services. The first one, groovyShellService, is the networked wrapper around the InteractiveShell. The second one, groovyConsoleService, is a wrapper around the GroovyConsole, which is a Swing-based application that provides essentially the same facility as the InteractiveShell, but in an application with a nice GUI. Since only the GroovyShellService allows remote access to an application it is focus of this article. But if you're running the server application on the same machine you're developing on, you can hit the URL http://localhost:8080/pimpmyshirt/launchGroovyConsole.html, which will trigger a simple Spring web controller to launch an instance of the GroovyConsole. Just note that for some reason exiting the GroovyConsole will cause Tomcat to exit, but since I mostly use the GroovyShellService, and this is only intended for development and testing purposes, I haven't bothered to try and find out why this is.
Both services inherit from the groovyService abstract bean, which includes bindings for the shirtService, which is a service included in the PimpMyShirt application that we'll explore with Groovy, and an instance of ApplicationContextWrapper, which is a class that implement's Springs ApplicationContext and ApplicationContextAware interfaces. The ApplicationContextWrapper is given a reference to the Spring application context through the ApplicationContextAware interface, and delegates all of ApplicationContext's methods to this instance. I did this because I didn't want the GroovyServices to be dependent on Spring, and while there might very well be a simpler way to pass an instance of the application context to a bean without implementing ApplicationContextAware, I don't know what it is.
After building the application with the included ant script, a war file is produced that it should be possible to deploy to any J2EE application server (although I've only tested it with Tomcat). Once it's deployed and launched, the first thing to do is to connect to the web application at http://hostname:8080/pimpmyshirt/index.html and enter some ratings for the shirts, in order to have some data in the application before we test it:
|There are no images attached to this page.|
Now we can connect to the GroovyServer and run some code to display the application's state. As configured, the application will launch the server on port 6789 when it starts, so assuming the application is running on the same machine you're sitting in front of, you can connect to it by just opening a shell and typing telnet localhost 6789. What you'll see is exactly what you'd get if you were to run groovysh on it's own:
We can now issue commands to the interpreter and see the results:
This code uses a Groovy closure to iterate over the ratings for available shirts and prints out the stats for each one. I won't explain Groovy syntax in detail as I go through these examples, since full documentation on programming in Groovy can be found on the Groovy web site. However, before going further I need to point out one difference between executing Groovy in this environment compared to its typical usage. You'll note that in the above example I've used "out.println" instead of just "println," as is usually the case in Groovy code. This is because in normal Groovy "println" writes to System.out, and in a server application, System.out is usually redirected to a log file, which is not where we usually want the output of our scripts to go. To work around this, the GroovyShellService passes in the socket's OutputStream bound to the token "out." So to print to the interactive console, we need to use "out.println" instead of just "println." Although there are other ways to work around this problem, which might be more transparent from the point of view of a user of the shell, I've chosen to do it this way since it's the easiest to implement, and the most explicit with regards to what's actually happening under the covers.
Note that since we've configured the GroovyServer in the Spring application context to have a binding to "shirtService," it's already available to us. If we hadn't done so, we could've also gotten a reference to the service from the application context by prepending the following to the code snippet above:
We can also call methods on the Spring application context to see, for example, what beans are available:
And in addition to the application services that are defined in the Spring context, we can also interrogate the web and application server layers to see how they're configured. For example, we could get the ServletContext from Spring and display its attribute names and values:
We can see from this output that Spring's WebApplicationContext, in which the servlets that Spring uses to provide hooks into it's web framework are defined is bound to the ServletContext's "org.springframework.web.servlet.FrameworkServlet.CONTEXT.pimpmyshirt" attribute. If we wanted a list of which beans were configured in the WebApplicationContext, we could print them out by doing the following:
We could also explore further, and get an instance of the RateShirts view from Spring's ViewResolver:
Or we could get an instance of the RateShirts web controller and view the contents of it's model data after it's initialized:
Obviously this is a sample application with a single service that doesn't do very much, so there isn't that much more we can do with it that would be all that interesting. However, for a real application with dozens or more services that were reasonably complex, it shouldn't be hard to imagine the usefulness of being able to interact with them to test their functionality and experiment with using them.