Copy Page

You are not logged in. Any changes you make will be marked as anonymous. You may want to Log In if you already have an account. You can also Sign Up for a new account.

<p><table class="wysiwyg-macro" data-macro-name="excerpt" data-macro-parameters="atlassian-macro-output-type=BLOCK|hidden=true" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2V4Y2VycHQ6aGlkZGVuPXRydWV8YXRsYXNzaWFuLW1hY3JvLW91dHB1dC10eXBlPUJMT0NLfQ&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="RICH_TEXT"><tr><td class="wysiwyg-macro-body"><p>Overriding invokeMethod, getProperty and setProperty</p></td></tr></table></p>

<h1>ExpandoMetaClass - Overriding invokeMethod, getProperty and setProperty</h1>

<p>It is also possible to override the methods invokeMethod, getProperty and setPropety on ExpandoMetaClass thus allowing even more dynamic behaviour.</p>

<h3>Overriding invokeMethod</h3>

<p>As an example of overring invokeMethod, take this simple example:</p>
<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
class Stuff {
   def invokeMe() { "foo" }
}

Stuff.metaClass.invokeMethod = { String name, args ->
   def metaMethod = Stuff.metaClass.getMetaMethod(name, args)
   def result
   if(metaMethod) result = metaMethod.invoke(delegate,args)
   else {
      result = "bar"
   }
   result
}

def stf = new Stuff()

assert "foo" == stf.invokeMe()
assert "bar" == stf.doStuff()
</pre></td></tr></table>
<p>So what is happening here? Well firstly we've overriden invokeMethod by assigning it an appropriate closure, but in addition we first look-up a <a href="http://groovy.codehaus.org/api/groovy/lang/MetaMethod.html">MetaMethod</a> with the line:</p>
<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
def metaMethod = delegate.class.metaClass.getMetaMethod(name)
</pre></td></tr></table>
<p>A <a href="http://groovy.codehaus.org/api/groovy/lang/MetaMethod.html">MetaMethod</a> in Groovy is a method that is known to exist on the MetaClass whether added at runtime or whatever, thus we check if there is an existing <a href="http://groovy.codehaus.org/api/groovy/lang/MetaMethod.html">MetaMethod</a> and if there isn't we simply return &quot;bar&quot;, hence the behaviour of the assert statements is correct.</p>

<h3>Overriding getProperty and setProperty</h3>

<p>Again overriding getProperty and setProperty is similar to the above:</p>
<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
class Person {
   String name = "Fred"
}

Person.metaClass.getProperty = { String name ->
   def metaProperty = Person.metaClass.getMetaProperty(name)
   def result
   if(metaProperty) result = metaProperty.getProperty(delegate)
   else {
      result = "Flintstone"
   }
   result
}

def p = new Person()

assert "Fred" == p.name
assert "Flintstone" == p.other
</pre></td></tr></table>
<p>The important thing to note here is that instead of a MetaMethod we look-up a <a href="http://groovy.codehaus.org/api/groovy/lang/MetaProperty.html">MetaProperty</a> instance if that exists we call the getProperty method of the <a href="http://groovy.codehaus.org/api/groovy/lang/MetaProperty.html">MetaProperty</a> passing the delegate (ie the instance of the class).</p>

<p>The only different with setProperty is you need the value in the method signature and to call setProperty on the MetaProperty:</p>
<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
Person.metaClass.setProperty = { String name, value ->
   ...
   if(metaProperty) metaProperty.setProperty(delegate, value)
   ...

}
</pre></td></tr></table>

<h3>Useful References</h3>

<ul>
	<li><a href="http://groovy.codehaus.org/api/groovy/lang/MetaMethod.html">MetaMethod</a></li>
	<li><a href="http://groovy.codehaus.org/api/groovy/lang/MetaProperty.html">MetaProperty</a></li>
</ul>