Extend Expression Language

el-config.xml

<mule>
  <configuration>
        <expression-language autoResolveVariables="false">
            <import name="loc" class="java.util.Locale" />
            <alias name="appName" expression="app.name" />
            <global-functions file="org/mule/test/el/functions.txt">
                def hello() {'Hello '+appName+'!'}
            </global-functions>
        </expression-language>
    </configuration>
  ...
</mule>