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Alex Soto

Using Groovy – A soft introduction

Groovy is an object-oriented programming language for the Java platform and can be used as a scripting language. Most of us but instead of using Groovy alone, we use Grails (web framework based on Groovy) for developing web applications.

But Groovy can be used standalone for developing your internal tools. Let me explain why Groovy scripts have simplified our development of tools for generating data for integration tests.
In my company we create clinical instruments. These instruments are so expensive, and big enough to say that they are not portable. For these reasons each instrument has an emulator, so integration tests are run without having physically any instrument.

Our emulator has an XML file where all required resources for running tests are configured. In summary each file contains a list of blood barcodes, and reagent barcodes. In our case barcodes have a meaning (kind of resource, expiry date, checksum, …).

So one can think about creating a standard configuration file that is used in integration tests. It is a good idea if you don’t know that expiry date is expressed in months. So one day without knowing exactly why your tests begin to fail. The answer is obvious, resources have become expired. We need a (script ?) that updates this XML file so when a resource is becoming expired, its month field is changed.

Moreover not all resources should be updated. Some tests imply working with expired resources. For this reason some barcodes have special format that suggests that update should not be applied.

Because project is developed in Java, one can think about creating a small Java class that do all these work. But wait and think if this class would be small or not, we need a parser (DocumentBuilder), a method that walks all nodes and see if resource is expired or not (NodeList, Element.getAttribute(), …), and finally writing modifications to file. Furthermore, some barcodes contains special charachtrs that should be detected using a regular expression (Pattern, Matcher) for avoiding its update. Although this class is not difficult, it is far away from a small class with few lines.

But how about polyglot programming? Groovy can be a choice. Let’s see how Groovy deals with XML and Regular Expressions.

Imagine next XML file:

               <Sample diameter="10" barcode="A1"/>
        <Sample diameter="10" barcode="2"/>
        <Sample diameter="10" barcode="3"/>

Groovy and XML

Meanwhile in Java you create a DocumentBuilderFactory that returns a DocumentBuilder, and then call parse method, in Groovy is as simple as:

def root = new XmlParser().parseText(input)

and root variable points to root element of XML file.

And now imagine that you want to update all blood barcodes of given holder. With Java you will use an iterator over NodeList or using an XPath expression. See the simplicity with Groovy.

def samples = root.SampleHolder11.Samples.Sample.findAll();

samples.each { sample ->
                   def barcode = nextBarcode()
            sample.@barcode = barcode

See that with Groovy, nodes are explored as object attributes, and finally we call findAll() method that returns a list of sample nodes belonging to SampleHolder11 tag. For returning an attribute value is as easy as adding @ character before attribute name, in our case barcode.

And for writing an XML is as easy as:

def writer = new StringWriter()
new XmlNodePrinter(new PrintWriter(writer)).print(root)
println writer.toString()

In previous example, output is written to console.

Groovy and Regular Expressions

Remember that some barcodes have special format. In our case if any barcode starts with A, B, C or D, should not be modified. A clean, reusable and maintainable solution is using regular expressions to check if one barcode matches or not special format. In Java the process is not banal, you have to create a Pattern object with a regular expression, a Matcher and use find() method to see if pattern is found on entry or not.

But how we can determine if one string matches a regular expression in Groovy ? ==~ operator does the work for us. Tell me what you think about this expression:

def currentBarcode = sample.@Barcode as String

if( currentBarcode ==~/([ABCD]).+/ ) {

Elementary. You will agree with me that Groovy approach is simpler than Java one.  For specifying a pattern you only have to use ~ character plus a slash (/) then a regular expression and finally a slash to delimit. But Groovy also supports =~ (create a Matcher) and ==~ (return boolean, whether String matches the pattern).

I think that creating a script that reads/parses/writes XML file is so fast and easy, not much classes are involved compared to Java. And not worth making the comparison with regular expression approach, in Groovy is the simplest way one may think.

After the success of previous Groovy script, we decided to create another tool (Groovy script) for manipulating database.

System registers into database every incidence that has occurred to an execution. Some incidences are easy to reproduce with emulator, but others not. In integration tests there is no problem, because a defined-filled database is used, but acceptance tests contains no data and is generated with the execution of tests. But because there are some incidences that are hard to reproduce in emulator, a Groovy script to insert incidences are created.

Groovy and SQL

As Java, Groovy can also access to databases and as you can suppose in a simple way. No Connection object, no PreparedStatement, no ResultSet, ….

Let’s see an example of searching data and using them for creating a new registry. Imagine that we have a table called Execution and another one called Incidence, and one-to-many relationship.

def db = Sql.newInstance(databaseUrl, user, password,  driverClass)

def findExecutionByNameSql = "SELECT * FROM execution as e WHERE e.name=?"
def insertIncidenceSql = "INSERT INTO incidence VALUES(?,?,?)"

def name = "myExecution"
def incidence = "NOT_DISPENSED"

db.eachRow(findExecutionByNameSql, [name]) { execution -> 
  def nextval = nextval();
  db.execute(insertIncidenceSql, [nextval, incidence, execution.dboid])

Simple, yes? With one line a connection to database is established.

Executing SELECT query and iterate over results are also easy. Using eachRow method, all results are iterated. No ResultSet object is required anymore. Parameters values are passed between brackets ([]), and as XML each row is accessed using Closure. In previous example each row is mapped to execution variable. Moreover see how easy is read a value of each tuple. As in XML you access the value as a class attribute, no more getters of ResultSet methods, in example execution.dboid is used to refer to dboid field.

Finally execute method is used to update database.

Now that I have shown you some of nice features that Groovy offers us, I will explain you how we execute these tools.


We use Jenkins with Maven as Continuos Integration System. Before Jenkins starts to execute Integration Tests, Groovy scripts are executed so emulator is configured propertly. The interesting part of this step is how pom is configured for executing Groovy scripts.

Exists a plugin called gmaven-plugin. This plugin runs Groovy scripts depending on phase and goal.



















No problem configuring gmaven plugin, the most important part is where you specify which script should be executed.

As final notes I want to say that I am a huge fan of Java and my intention is not criticize it, but I think that there are some problems that are best suited using other languages rather than Java. My advice is  learning as many kind of languages as you can (Scala, Groovy, …) so as programmer you can choose the best solution to a given problem.

I wish you find this post useful.

Reference: Using Groovy – A soft introduction  from our JCG partner Alex Soto at the One Jar To Rule Them All blog

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