Transforming data in XML to several Java-Objects is a pretty common task. There are a lot of technologies that support this. One example would be JAXB. It is also not uncommon that the structure of the original XML and the Java objects does not match. The obvious choice for XML transformation in such a situation would be XSLT.
There is another approach that uses Groovy to transform XML directly into a POJO structure in one step. I will show you how this looks like.
Lets assume, we have a XML-file like this:
<data>
<person>
<firstname>Otto</firstname>
<lastname>Mueller</lastname>
<street>Lange Strasse</street>
<city>Berlin</city>
</person>
<financial>
<netincome>120000</netincome>
</financial>
</data>
The target structure are two POJOs that look like this:
Both structures differ. There are also some small conversions to do. The XML includes yearly income, where the POJOs needs monthly income. The POJOs contains a field for zipcode, but the XML does not deliver it.
So, here is the Groovy-Code that does all the transformation:
public class XmlTransformer
{
Person transform(File xml) //1
{
def xmlData = new XmlSlurper().parse(xml) //2
Person person = new Person()
person.firstName = xmlData.person.firstname //3
person.lastName = xmlData.person.lastname
Address address = new Address()
address.city = xmlData.person.city
address.street = xmlData.person.street
address.zipCode = ZipCodeFinder.find(xmlData.person.city.toString(), //4
xmlData.person.street.toString())
person.address = address
BigInteger yearlyIncome = new BigInteger(xmlData.financial.netincome.toString())
person.monthlyIncome = yearlyIncome.divide(12) //5
return person
}
}
What happens in detail (numbers on the list match the numbers in code comments):
- This is a simple Groovy class that contains one method called transform. This method gets the XML-file as input and returns a Person object. The Person class itself is defined in Java.
- XMLSlurper is the Groovy XML-Parser that allows the easy access to all xml elements. For more details on it see here.
- This uses some Groovy magic. On the left side we assign the value to the property firstName of the person object. This is a shortcut for using person.setFirstName(). On the right side we see the slurper at work to get us the XML value.
- We can call any Java-class from within the transformation code. Here we call an example helper-class, that would return a zipcode for a given city and street.
- Finally we also do some calculations within our transformation to convert the yearly income to a monthly value.
Groovy can be called from Java in several ways. If you do not need to change the transformation often I recommend to just compile the Groovy code. In that case it will be called from Java as if it would be Java code:
XmlTransformer transformer = new XmlTransformer();
Person person = transformer.transform(inputFile);
This kind of transformation code can easily be embedded into a Java project. There are several advantages, when using the Groovy method:
- Just one step for transformation including conversions.
- Easy debugging, when using an IDE like IntelliJ IDEA.
- Java-like syntax, no learning of XSLT required.
- Easy code-structuring. The transformation can use all features of a dynamic object-oriented language.
- Simple unit-testing. If you split the code into several methods, you can test each logical unit using established frameworks like JUnit or TestNG.
So what is your opinion? What are your current methods of transforming XML to POJOs?
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