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Using ExpandoMetaClass to add behaviour

Groovy 1.1 includes a special MetaClass called an ExpandoMetaClass that allows you to dynamically add methods, constructors, properties and static methods using a neat closure syntax.

How does it work? Well every java.lang.Class is supplied with a special "metaClass" property that when used will give you a reference to an ExpandoMetaClass instance.

For example given the Java class java.lang.String to obtain its ExpandoMetaClass you can use:

Code Block
String.metaClass.swapCase = {->
      def sb = new StringBuffer()
      delegate.each {
           sb << (Character.isUpperCase(it as char) ? Character.toLowerCase(it as char) : 
                   Character.toUpperCase(it as char))
      }
      sb.toString()
}

This adds a method called swapCase to the String class.

Note

By default ExpandoMetaClass doesn't do inheritance. To enable this you must call ExpandoMetaClass.enableGlobally() before your app starts such as in the main method or servlet bootstrap

Further Reading:

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