Loading Classes in Adobe CQ

So you’ve got a problem. You need to load a resource from the Classpath or you need to dynamically load a class and you’re using Adobe CQ. Since Adobe CQ uses an OSGi container, a regular ClassLoader will not be able to retrieve the class information from the OSGi Bundles.

Never fear, Apache Sling provides the Dynamic ClassLoader Service. This OSGi Service allows you to retrieve a ClassLoader which will allow you to interact with classes contained in OSGi Bundles.

Using the Service

Using the service is easy, simply retrieve an instance of the service org.apache.sling.commons.classloader.DynamicClassLoaderManager and call the method getDynamicClassLoader().

In JSP scripts, you can simply use the Sling Script Helper:

<%
  DynamicClassLoaderManager classLoaderManager = sling.getService(DynamicClassLoaderManager.class);
  ClassLoader classLoader = classLoaderManager.getDynamicClassLoader();
  [... Use the ClassLoader ...]
%>

OSGi Services can just use a Reference to load the DynamicClassLoaderManager

@Reference
private DynamicClassLoaderManager classLoaderManager;

Tags need to first retrieve the SlingBindings and then retrieve the Script Helper to get the DynamicClassLoaderManager.

final SlingBindings bindings = (SlingBindings) pageContext.getRequest()
	.getAttribute(SlingBindings.class.getName());
final SlingScriptHelper scriptHelper = bindings.getSling();
final DynamicClassLoaderManager dynamicClassLoaderManager = 
	scriptHelper.getService(DynamicClassLoaderManager.class);

Once you have the ClassLoader, it can be used like any other ClassLoader to retrieve resources from the Classpath or dynamically retrieve Classes.