Groovy - XML


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XML is a portable, open source language that allows programmers to develop applications that can be read by other applications, regardless of operating system and/or developmental language. This is one of the most common languages used for exchanging data between applications.

What is XML?

The Extensible Markup Language XML is a markup language much like HTML or SGML. This is recommended by the World Wide Web Consortium and available as an open standard. XML is extremely useful for keeping track of small to medium amounts of data without requiring a SQLbased backbone.

XML Support in Groovy

The Groovy language also provides a rich support of the XML language. The two most basic XML classes used are −

  • XML Markup Builder − Groovy supports a tree-based markup generator, BuilderSupport, that can be subclassed to make a variety of tree-structured object representations. Commonly, these builders are used to represent XML markup, HTML markup. Groovy’s markup generator catches calls to pseudomethods and converts them into elements or nodes of a tree structure. Parameters to these pseudomethods are treated as attributes of the nodes. Closures as part of the method call are considered as nested subcontent for the resulting tree node.

  • XML Parser − The Groovy XmlParser class employs a simple model for parsing an XML document into a tree of Node instances. Each Node has the name of the XML element, the attributes of the element, and references to any child Nodes. This model is sufficient for most simple XML processing.

For all our XML code examples, let's use the following simple XML file movies.xml for construction of the XML file and reading the file subsequently.

<collection shelf = "New Arrivals"> 

   <movie title = "Enemy Behind"> 
      <type>War, Thriller</type> 
      <format>DVD</format> 
      <year>2003</year> 
      <rating>PG</rating> 
      <stars>10</stars> 
      <description>Talk about a US-Japan war</description> 
   </movie> 
	
   <movie title = "Transformers"> 
      <type>Anime, Science Fiction</type>
      <format>DVD</format> 
      <year>1989</year> 
      <rating>R</rating> 
      <stars>8</stars> 
      <description>A schientific fiction</description> 
   </movie> 
	
   <movie title = "Trigun"> 
      <type>Anime, Action</type> 
      <format>DVD</format> 
      <year>1986</year> 
      <rating>PG</rating> 
      <stars>10</stars> 
      <description>Vash the Stam pede!</description> 
   </movie> 
	
   <movie title = "Ishtar"> 
      <type>Comedy</type> 
      <format>VHS</format> 
      <year>1987</year> 
      <rating>PG</rating> 
      <stars>2</stars> 
      <description>Viewable boredom </description> 
   </movie> 
	
</collection> 

XML Markup Builder

Syntax

public MarkupBuilder()

The MarkupBuilder is used to construct the entire XML document. The XML document is created by first creating an object of the XML document class. Once the object is created, a pseudomethod can be called to create the various elements of the XML document.

Let’s look at an example of how to create one block, that is, one movie element from the above XML document −

Live Demo
import groovy.xml.MarkupBuilder 

class Example {
   static void main(String[] args) {
      def mB = new MarkupBuilder()
		
      // Compose the builder
      mB.collection(shelf : 'New Arrivals') {
         movie(title : 'Enemy Behind')
         type('War, Thriller')
         format('DVD')
         year('2003')
         rating('PG')
         stars(10)
         description('Talk about a US-Japan war') 
      }
   } 
}

In the above example, the following things need to be noted −

  • mB.collection() − This is a markup generator that creates the head XML tag of <collection></collection>

  • movie(title : 'Enemy Behind') − These pseudomethods create the child tags with this method creating the tag with the value. By specifying a value called title, this actually indicates that an attribute needs to be created for the element.

  • A closure is provided to the pseudomethod to create the remaining elements of the XML document.

  • The default constructor for the class MarkupBuilder is initialized so that the generated XML is issued to the standard output stream

When we run the above program, we will get the following result −

<collection shelf = 'New Arrivals'> 
   <movie title = 'Enemy Behind' /> 
      <type>War, Thriller</type> 
      <format>DVD</format> 
      <year>2003</year> 
      <rating>PG</rating> 
      <stars>10</stars> 
      <description>Talk about a US-Japan war</description> 
   </movie> 
</collection>

In order to create the entire XML document, the following things need to be done.

  • A map entry needs to be created to store the different values of the elements.
  • For each element of the map, we are assigning the value to each element.
Live Demo
import groovy.xml.MarkupBuilder 

class Example {
   static void main(String[] args) {
      def mp = [1 : ['Enemy Behind', 'War, Thriller','DVD','2003', 
         'PG', '10','Talk about a US-Japan war'],
         2 : ['Transformers','Anime, Science Fiction','DVD','1989', 
         'R', '8','A scientific fiction'],
         3 : ['Trigun','Anime, Action','DVD','1986', 
         'PG', '10','Vash the Stam pede'],
         4 : ['Ishtar','Comedy','VHS','1987', 'PG', 
         '2','Viewable boredom ']] 
			
      def mB = new MarkupBuilder()  
		
      // Compose the builder
      def MOVIEDB = mB.collection('shelf': 'New Arrivals') {
         mp.each {
            sd -> 
            mB.movie('title': sd.value[0]) {  
               type(sd.value[1])
               format(sd.value[2])
               year(sd.value[3]) 
               rating(sd.value[4])
               stars(sd.value[4]) 
               description(sd.value[5]) 
            }
         }
      }
   } 
} 

When we run the above program, we will get the following result −

<collection shelf = 'New Arrivals'> 
   <movie title = 'Enemy Behind'> 
      <type>War, Thriller</type> 
      <format>DVD</format> 
      <year>2003</year> 
      <rating>PG</rating> 
      <stars>PG</stars> 
      <description>10</description> 
   </movie> 
   <movie title = 'Transformers'> 
      <type>Anime, Science Fiction</type> 
      <format>DVD</format> 
      <year>1989</year>
	  <rating>R</rating> 
      <stars>R</stars> 
      <description>8</description> 
   </movie> 
   <movie title = 'Trigun'> 
      <type>Anime, Action</type> 
      <format>DVD</format> 
      <year>1986</year> 
      <rating>PG</rating> 
      <stars>PG</stars> 
      <description>10</description> 
   </movie> 
   <movie title = 'Ishtar'> 
      <type>Comedy</type> 
      <format>VHS</format> 
      <year>1987</year> 
      <rating>PG</rating> 
      <stars>PG</stars> 
      <description>2</description> 
   </movie> 
</collection> 

XML Parsing

The Groovy XmlParser class employs a simple model for parsing an XML document into a tree of Node instances. Each Node has the name of the XML element, the attributes of the element, and references to any child Nodes. This model is sufficient for most simple XML processing.

Syntax

public XmlParser() 
   throws ParserConfigurationException, 
      SAXException

The following codeshows an example of how the XML parser can be used to read an XML document.

Let’s assume we have the same document called Movies.xml and we wanted to parse the XML document and display a proper output to the user. The following codeis a snippet of how we can traverse through the entire content of the XML document and display a proper response to the user.

import groovy.xml.MarkupBuilder 
import groovy.util.*

class Example {

   static void main(String[] args) { 
	
      def parser = new XmlParser()
      def doc = parser.parse("D:\\Movies.xml");
		
      doc.movie.each{
         bk->
         print("Movie Name:")
         println "${bk['@title']}"
			
         print("Movie Type:")
         println "${bk.type[0].text()}"
			
         print("Movie Format:")
         println "${bk.format[0].text()}"
			
         print("Movie year:")
         println "${bk.year[0].text()}"
			
         print("Movie rating:")
         println "${bk.rating[0].text()}"
			
         print("Movie stars:")
         println "${bk.stars[0].text()}"
			
         print("Movie description:")
         println "${bk.description[0].text()}"
         println("*******************************")
      }
   }
} 

When we run the above program, we will get the following result −

Movie Name:Enemy Behind 
Movie Type:War, Thriller 
Movie Format:DVD 
Movie year:2003 
Movie rating:PG 
Movie stars:10 
Movie description:Talk about a US-Japan war 
******************************* 
Movie Name:Transformers 
Movie Type:Anime, Science Fiction 
Movie Format:DVD 
Movie year:1989 
Movie rating:R 
Movie stars:8 
Movie description:A schientific fiction 
******************************* 
Movie Name:Trigun 
Movie Type:Anime, Action
Movie Format:DVD 
Movie year:1986 
Movie rating:PG 
Movie stars:10 
Movie description:Vash the Stam pede! 
******************************* 
Movie Name:Ishtar 
Movie Type:Comedy 
Movie Format:VHS 
Movie year:1987 
Movie rating:PG 
Movie stars:2 
Movie description:Viewable boredom

The important things to note about the above code.

  • An object of the class XmlParser is being formed so that it can be used to parse the XML document.

  • The parser is given the location of the XML file.

  • For each movie element, we are using a closure to browse through each child node and display the relevant information.

For the movie element itself, we are using the @ symbol to display the title attribute attached to the movie element.



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