Groovy | Vasanth Dharmaraj's Blog

Running standalone Groovy scripts

As I mentioned in my post Learning Groovy, I am writing Groovy scripts to automate some simple tasks. Now I want to share the scripts with others. I did not want them to install Groovy just to run the scripts. I had the groovy-all-1.8.0.jar, so I typed the following in the command prompt:

1 2	C:\temp>java -jar groovy-all-1.8.0.jar Hello.groovy Hello

It worked. Simple. Now I tried to run my script that retrieved the XMLs from a database.

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C:\work\FetchData>java -jar groovy-all-1.8.0.jar FetchData.groovy
Caught: java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver
at FetchData.fetch(FetchData.groovy:51)
at FetchData.run(FetchData.groovy:3)

Of course I need the driver jar in the classpath. So I added the sqljdbc.jar to the classpath.

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C:\work\FetchData>java -cp sqljdbc.jar -jar groovy-all-1.8.0.jar FetchData.groovy
Caught: java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver
at FetchData.createCSV(FetchData.groovy:51)
at FetchData.run(FetchData.groovy:3)

Looks like the script is run with a different classloader and the java classpath is not passed to it. I did some lazy googling but did not find the answer I was looking for. So I looked at how eclipse is doing it. Eclipse used GroovyStarter and GroovyMain to run scripts. Not knowing which to use, I just used GroovyMain:

1 2	C:\work\FetchData>java -cp lib/groovy-all-1.8.0.jar;lib/sqljdbc.jar groovy.ui.GroovyMain FetchData.groovy Fetched Data!

It worked! I just added the command in a batch file to share the script.

Learning Groovy

I have dabbled a bit with scripting languages before but for some reason never really used one long term. I think that might change with Groovy. A colleague of mine got me interested in it and I have been picking up all the cool things Groovy can do by reading Dustin’s “Inspired by Actual Events” blog. Come to think of it Groovy could have saved me a ton of time I spent in writing small tools to help me in development.

I like the how concise and simple writing groovy scripts are. Here is a snippet of code to print rows retrieved from a database.

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// Get instance of Groovy's Sql class
// See http://marxsoftware.blogspot.com/2009/05/groovysql-groovy-jdbc.html
import groovy.sql.Sql

def sql = Sql.newInstance("jdbc:oracle:thin:@localhost:1521:orcl", "hr", "hr", "oracle.jdbc.pool.OracleDataSource")

// iterate over query's result set and "process" each row by printing two names
sql.eachRow("SELECT employee_id, last_name, first_name FROM employees")
{
println "Employee ${it.first_name} ${it.last_name} has ID of ${it.employee_id}."
}

At work I needed to retrieve about 100 XMLs stored in a database, strip out some tags from it and write it to a file. It took about 15 lines of Groovy code to do it. Probably could have done it in less but I am just learning Groovy.

Here is another way to use Groovy that I wish I knew before. Embedding Groovy in Ant:


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 <zipfileset id="found" src="foobar.jar"

             includes="**/*.xml"/>

 <groovy>

     project.references.found.each {

         println it.name

     }

 </groovy>

Though the above snippet is simple, it shows how the Groovy script is aware of the Ant references. Pretty powerful.

I will showcase just another snippet before I am off to learn more Groovy. Invoking a web service:

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@Grab(group='org.codehaus.groovy.modules', module='groovyws', version='0.5.2')
import groovyx.net.ws.WSClient

proxy = new WSClient("http://www.w3schools.com/webservices/tempconvert.asmx?WSDL", this.class.classLoader)
proxy.initialize()

result = proxy.CelsiusToFahrenheit(0)
println "You are probably freezing at ${result} degrees Farhenheit"