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Groovy and XML

groovy straw

Manipulating with XML in some easy way is part of my journey to get an easy way to change WildFly standalone.xml. Use of the Groovy and its tools came to me with tool Creaper which I use in testsuites I work on. (Creaper came from hands of my collegue Láďa Thon). The Creaper tool let you make changes of the configuration either through CLI commands or with use of Groovy XML modification.

Here I would like to sum up so of my observation of using XML with Groovy. Mostly similar to nice article at

WARN: DISCLAIMER. I’m not fully sure with accuracy of all the terms used below. I recommend to check the net. And let me know about issues here.

XML manipulation in Groovy in brief

One is XMLParser (GPath expressions could be used, GPath is a path expression language) and here is an example

def scopeNode = asNode().depthFirst().find {
  println == 'scope'
the method find is method of the Groovy object Object.

The XmlSlurper allows to parse an XML document and returns an GPathResult object. You can use GPath expressions.

XMLSlurper in more details

As the Creaper uses XMLSlurper I played more with it.

My point here is show some Groovy language picks that wasn’t obvious for me as I’m quite a nebiew in.

To start work with the XMLSlurper I use groovyConsole - just start it and copy&paste.

import groovy.xml.XmlUtil

xml =
'''<server xmlns="urn:jboss:domain:4.0">
    <subsystem xmlns="urn:jboss:domain:iiop-openjdk:1.0">
      <initializers transactions="spec" security="identity"/>
         <property name="propname" value="propvalue" />

// to get the variable printed to see the content
print xml

def root = new XmlSlurper().parseText(xml)

// get back the xml processed with XMLSlurper as a string
def writer = new StringWriter()
XmlUtil.serialize(root, writer);
print writer.toString()

Now the root contains the xml tree that could be navigated as groovy.util.slurpersupport.GPathResult ( attributes with dot notation (.). The root itself is type of groovy.util.slurpersupport.NodeChildren ( which is defined as lazy evaluated representation of child nodes and it’s a child of the GPathResult class itself.

When using dot notation it’s easy to work with existing xml emlements

// having a subtree variable for further use
iiop = root.profile.subsystem
// changing existing attribute
iiop.initializers.@security = 'who needs security?'
// adding non-existing attribute to an existing node
iiop.initializers.'@my.attribute' = 'chalda'

To check documentaiton on types you work with see

assert groovy.util.slurpersupport.Attributes ==
assert groovy.util.slurpersupport.Attribute ==

Chaning attributes

For saving a value of an attribute (attribute of a xml element) you can use method text()

assert 'identity' == iiop.initializers.@security.text()
assert '' == iiop.initializers.@'non-existent'.text()

def m = [:]
println iiop.initializers*.attributes()
  .collectMany { it.entrySet() }
  .each { m.put(it.key, it.value) }
assert m == [security:'identity', transactions:'spec']

m = [:] {
  list << it.@name
  m << [(it.@name.text()): it.@value.text()]
assert m == ['propname':'propvalue']

When constructing the GPathResult definition you can use GString expressions

def t = 'transactions'
assert 'spec' == iiop.initializers."@${t}".text()

Removing attributes

Having chance to remove an attribute there is need to touch actual groovy.util.slurpersupport.Node ( or groovy.util.slurpersupport.NodeChild (

When you get the node you can start working with its name or attributes as you need. To get a node I got used to call one of methods which returns Iterator. There is a method iterator() which provides NodeChild or there is a method nodeIterator() which provides Node. For sure there are plenty other ways to get nodes as for example method findAll() and others.

Another way is usage of star-dot operator (a shortcut operator allowing you to call a method on all elements of a collection).

Node iteration

To iterate over all nodes at the current level - here it means iterating over all initializers nodes.

// -> class groovy.util.slurpersupport.NodeChild
iiop.initializers.iterator().each {
  println it.getClass()

// -> class groovy.util.slurpersupport.Node
iiop.initializers.nodeIterator().each {
  println it.getClass()

// -> class groovy.util.slurpersupport.NodeChild
iiop.initializers.findAll({true}).each {
  println it.getClass()

// -> class groovy.util.slurpersupport.NodeChild
println iiop.initializers*.getClass()

Child nodes iteration

Iterating over child nodes of the current level of nodes, use method childNodes() or children().

// -> class groovy.util.slurpersupport.Node
iiop.childNodes().each {
  println it.getClass()

// -> class groovy.util.slurpersupport.NodeChild
iiop.children().each {
  println it.getClass()

For iteration over all nodes in the xml tree (traversing recursively) you need to use GPath methods breadthFirst or depthFirst.

root.breadthFirst().each { println }

More on removing attributes

Removing an attribute is then piece of cake. Of course it could be done in multiple ways.

iiop.initializers.nodeIterator().each {
iiop.initializers*.attributes().each {it.remove('transactions')}

Obviously you can use a find method to get single (first matching) result in this case it will be a type NodeChild.

assert 1 == iiop.initializers.find {it.'@transactions' == 'spec'}.size()

Removing nodes

What about removing a node? It’s done by one of method replaceNode (if the current node itself is involved) or replaceBody (if content of the current node is involved). Methods accept a closure as parameter. The closure represents a new structure of the node. When the closure is empty then the node is removed.

iiop.initializers.replaceNode {}
iiop.replaceBody {}

Appending nodes

The other method which works with closure as representation of a node structure is appendNode.

Both methods works with the fact that call of the closure is delegated. Delegation references a special handling of unknown method calls which are part of the closure definition. Any unknown method call is then considered as definition of a new xml element and it’s method parameters as attributes. You can then define a closure which is in fact definition of xml structure. That one could be passed to a appendNode method.

// -- node append
iiop.appendNode {
  'as-context' ('caller-propagation': 'supported')

// -- closure definition which is added as node later on
// properties to add definition
def myprops = ['goodone':'Frodo', 'evilone':'Saruman']
def props = {
  // unknown method 'properties' called with argument closure
     which defines an child xml element
  properties {
    // any call of 'property' defines an xml element where
       named arguments defines attributes
    for(itemkey in myprops.keySet()) property('name': itemkey, 'value': myprops.get(itemkey))
    // or add a new element named 'property-def' with attributes
       being defined by map 'myprops'
iiop.appendNode props

There is one shortcut as operator << (leftShift) is overloaded and could be used instead of method appendNode.

There could be a different ways for adding a node to an element

// first getAt returns 'NodeChild', the second getAt returns 'Node'
iiop.initializers.getAt(0).getAt(0).addChild({ good() })
iiop.initializers.nodeIterator().next().addChild({ 'really-good'() })

Groovy does not require using brackets to pass parameters to a method call - e.g.

iiop << { 'as-context' ('caller-propagation': 'supported') }

has the same effect as

iiop << { 'as-context' 'caller-propagation': 'supported' }

But when you want to pass a parameters as a map, then this

iiop << { 'as-context' ['caller-propagation': 'supported'] }

doesn’t work and you have to use parenthesis as this is a special case.

Additional notes

  • iiop << { test } does nothing as expression test itself is not a method call

  • iiop << { test() } produces <test/> as test() is a method call

  • iiop << { test(){} } produces <test/> as `test(){} is a method call with a parameter of empty closure

  • iiop << { test{} } produces <test/> as test {} is a method call with one parameter which is an empty closure (Groovy does not require parenthesis to separate method arguments definition test {} is the same as test ({}))

  • one unnamed parameter defines a text which is added to the xml element iiop << { test ('mytext') } generates <test>mytext</test>.

  • extending the previous point iiop << { test 'mytext' } generates the same element with text <test>mytext</test>

  • for multiple method parameters only the last one is considered iiop << { test('mytext', 'mytext2') } produces <test>mytext2</test>

  • as it depends on order the content of closure could be ignored as well iiop << { test({innerelement()}, 'mytext') } produces element with text <test>mytext</test>. I haven’t found a way how to add a text for element and a new child element at the same time.

  • named parameters are not considered when element receives as argument a map. Both definition generates the same <test mapid="mapvalue"/>: def mymap = ['mapid': 'mapvalue']; iiop << {test('param1': 'value1', mymap)} versus def mymap = ['mapid': 'mapvalue']; iiop << {test(mymap, 'param1': 'value1')}

  • when needed to add a nothing then use null def isTest = false; iiop << { isTest ? 'test'() : null }

If you want to check for existence of a node you are stick with checking size of the result set.

assert iiop.'non-existing-element'.isEmpty()
assert 0 == iiop.'non-existing-element'.size()
assert 0 == iiop.initializers.'@non-existing-attribute'.size()
assert 1 == iiop.initializers.'@transactions'.size()

For sure there is a chance to add a new method to write shorter more comprehensible code.

groovy.util.slurpersupport.GPathResult.metaClass.exists = {->
    return delegate.size() > 0
groovy.util.slurpersupport.GPathResult.metaClass.notExists = {->
    return delegate.size() <= 0

assert iiop.'non-existing-element'.notExists()
assert iiop.initializers.exists()

On checking and appending nodes there is a one trap. At least in my eyes.

if(iiop.'as-context'.isEmpty()) iiop.appendNode {
  'as-context' ('caller-propagation': 'supported')
assert iiop.'as-context'.isEmpty() // true

I haven’t found any good solution yet outside to count with this and not trying to write a code which do so.

Creaper offline command for datasource manipulation

Published Oct 2, 2017

Developer notes.