Given the xml from your comment:
def x = '''<?xml version="1.0" encoding="utf-8"?>
|<FxCopReport Version="11.0">
| <Namespaces>
| <Namespace Name="RWSTestXDT">
| <Messages>
| <Issue Name="Namespace" Certainty="85" Level="Error"></Issue>
| </Messages>
| </Namespace>
| </Namespaces>
| <Targets>
| <Target>
| <Modules>
| <Module Name="rwstestxdt.dll">
| <Messages>
| <Issue Name="NoStrongName" Certainty="95" Level="CriticalError"></Issue>
| </Messages>
| </Module>
| </Modules>
| </Target>
| </Targets>
|</FxCopReport>'''.stripMargin()
You can do:
List<String> levels = new XmlSlurper().parseText( x )
.'**'
.findAll { it.name() == 'Issue' }
.collect { it.@Level.text() }
To get the list:
[ 'Error', 'CriticalError' ]