Exemplo de metaprogramação em Groovy

gistfile1.java

//String - crypt()
String.metaClass.crypt = { ->
	return org.apache.commons.codec.digest.DigestUtils.md5Hex(delegate)
}

//String - isNumeric
String.metaClass.isNumeric = { ->
	return org.apache.commons.lang.StringUtils.isNumeric(delegate)	
}

//String - isBlank
String.metaClass.isBlank = { ->
	return org.apache.commons.lang.StringUtils.isBlank(delegate)	
}

//File - getExtension()
File.metaClass.getExtension = {
	
	def extension = ""
	def matcher = (delegate.name =~ /(\.[^\.]*)$/)
	if (matcher.size() > 0)
		extension = ((matcher[0][0].size()>0) ? matcher[0][0].substring(1).trim().toLowerCase() : "")
	return extension
	
}