This gist is fork from https://gist.github.com/870666 by @kyon_mm

keyValueXml4.groovy

/**
* Created by IntelliJ IDEA.
* User: kyon
* Date: 11/03/15
* Time: 0:54
* To change this template use File | Settings | File Templates.
*/

String.metaClass.toXML = { builder, entry ->
  builder."${entry.key}"(entry.value)
}

LinkedHashMap.metaClass.toXML = { builder, entry ->
  builder."${entry.key}" {
    entry.value.each { it.toXML(builder) }
  }
}

LinkedHashMap$Entry.metaClass.toXML = { builder ->
  delegate.value.toXML(builder, delegate)
}

def kvmap = [
  key1: "value1",
  key2: "value2",
  key3: [
    "key3-1" : "value3-1",
    "key3-2" : "value3-2",
  ],
]

def sw = new StringWriter()
def xml = new groovy.xml.MarkupBuilder(sw)
xml.doubleQuotes = true // 属性はダブルクォートだよね！
xml.langs(type: 'current') {
  kvmap.each {
    it.toXML(xml)
  }
}

def expect = '''\
<langs type="current">
  <key1>value1</key1>
  <key2>value2</key2>
  <key3>
    <key3-1>value3-1</key3-1>
    <key3-2>value3-2</key3-2>
  </key3>
</langs>'''
assert sw.toString() == expect