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<h1>Using invokeMethod &amp; getProperty</h1>

<p>Since 1.0, Groovy supports the ability to intercept <em>all</em> method and property access via the <code>invokeMethod</code> and <code>get/setProperty</code> hooks. If you only want to intercept failed method/property access take a look at <a class="confluence-link" href="/display/GROOVY/Using+methodMissing+and+propertyMissing" data-linked-resource-id="9765917" data-linked-resource-type="page" data-linked-resource-default-alias="Using methodMissing and propertyMissing" data-base-url="http://docs.codehaus.org">Using methodMissing and propertyMissing</a>.</p>

<h2>Overriding invokeMethod</h2>

<p>In any Groovy class you can override <code>invokeMethod</code> which will essentially intercept all method calls (to intercept calls to existing methods, the class additionally has to implement the <code>GroovyInterceptable</code> interface). This makes it possible to construct some quite interesting DSLs and builders.</p>

<p>For example a trivial <code>XmlBuilder</code> could be written as follows (note Groovy ships with much richer XML APIs and this just serves as an 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 XmlBuilder {
   def out
   XmlBuilder(out) { this.out = out }
   def invokeMethod(String name, args) {
       out &lt;&lt; "&lt;$name>"
       if(args[0] instanceof Closure) {
            args[0].delegate = this
            args[0].call()
       }
       else {
           out &lt;&lt; args[0].toString()
       }
       out &lt;&lt; "&lt;/$name>"
   }
}
def xml = new XmlBuilder(new StringBuffer())
xml.html {
    head {
        title "Hello World"
    }
    body {
        p "Welcome!"
    }
}
</pre></td></tr></table>

<p>Another simple usage of invokeMethod is to provide simple AOP style around advice to existing methods. Here is a simple logging example implemented with invokeMethod:</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 MyClass implements GroovyInterceptable {
    def invokeMethod(String name, args) {
    
        System.out.println ("Beginning $name")
        def metaMethod = metaClass.getMetaMethod(name, args)
        def result = metaMethod.invoke(this, args)
        System.out.println ("Completed $name")
        return result 
    }
}
</pre></td></tr></table>

<h2>Overriding getProperty and setProperty</h2>

<p>You can also override property access using the <code>getProperty</code> and <code>setProperty</code> property access hooks. For example it is possible to write a trival &quot;Expandable&quot; object using this technique:</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 Expandable {
    def storage = [:]
    def getProperty(String name) { storage[name] }
    void setProperty(String name, value) { storage[name] = value }
}

def e = new Expandable()
e.foo = "bar"
println e.foo
</pre></td></tr></table>