Practically Groovy: Go Server-Side Up, with Groovy
By Andrew Glover2005-05-05
A Diagnostic Groovlet
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Not only is writing a Groovlet as simple as creating a Groovy script but you can also define functions with the def keyword and call them directly within the Groovlet. To demonstrate, I'll create a nontrivial Groovlet that performs some diagnostic checks for a Web application.
Imagine you've written a Web application that has been purchased by various customers around the world. You have a large customer base and have been releasing this application for some time now. Learning from past support issues, you've noticed that you receive many frantic customer calls related to a problem stemming from incorrect JVM versions and incorrect object-relational mapping (ORM).
You're busy, so you ask me to come up with a solution. Using Groovlets, I quickly can create a simple diagnostic script that verifies the VM version and attempts to create a Hibernate session (see Resources). I start by creating two functions and calling them when the script is hit via a browser. The diagnostic Groovlet is defined in Listing 6:
Listing 6. A diagnostic Groovlet
import com.vanward.resource.hibernate.factory.DefaultHibernateSessionFactoryThe Groovlet's verification logic is fairly simple, but it will do the trick. You'll simply bundle the diagnostic script with your Web application, and when your customer support desk receives a call, they'll point the customer to the Diagnostics.groovy script in their browser and ask them to report their findings. The results could look something like what you see in Figure 2.
/**
* Tests VM version from environment- note, even 1.5 will
* cause an assertion error.
*/
def testVMVersion(){
println "<h3>JVM Version Check: </h3>"
vers = System.getProperty("java.version")
assert vers.startsWith("1.4"): "JVM must be at least 1.4"
println "<p>JVM version: ${vers} </p>"
}
/**
* Attempts to create an instance of a hibernate session. If this
* works we have a connection to a database; additionally, we
* have a properly configured hibernate instance.
*/
def testHibernate(){
println "<h3>Hibernate Configuration Check: </h3>"
try{
sessFactory = DefaultHibernateSessionFactory.getInstance()
session = sessFactory.getHibernateSession()
assert session != null: "Unable to create hibernate session.
Session was null"
println "<p>Hibernate configuration check was successful</p>"
}catch(Throwable tr){
println """
<p>Unable to create hibernate session. Exception type is: <br/>
<i>${tr.toString()} </i><br/>
</p>
"""
}
}
println """
<html><head>
<title>Diagnostics Check</title></head>
<body>
"""
testVMVersion()
testHibernate()
println """
</body></html>
"""
Figure 2. Output from the diagnostic Groovlet
Tutorial Pages:
» On-the-fly Server-Side Programming with Groovlets and GSPs
» Defining Functions in Scripts
» Groovlets and GSPs
» The Groovlet, Please
» A Diagnostic Groovlet
» What About Those GSPs?
» Refactor me this ...
» Conclusion
» Resources
First published by IBM DeveloperWorks
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