Getting Resources and Properties in Sling

The Resource is one of the central parts of Sling. Extending from JCR's Everything is Content, Sling assumes Everthing is a Resource. Thus Sling is maintaining a virtual tree of resources, which is a merger of the actual contents in the JCR Repository and resources provided by so called resource providers. By doing this Sling fits very well in the paradigm of the REST architecture.

In this article we will explore a few ways to programmatically map a resource path (String) to a resource object (Resource) and its properties in Sling, from within an OSGI service, a servlet and a JSP.

The whole game consists in first getting a ResourceResolver and then getting the Resource itself.

Within an OSGI Service/Compoment

You can access a resource through the ResourceResolverFactory service:

/** @scr.reference */
private ResourceResolverFactory resolverFactory;

public void myMethod() {
    try {
	String resourcePath = "path/to/resource";
    	ResourceResolver resourceResolver = resolverFactory.getAdministrativeResourceResolver(null);
	Resource res = resourceResolver.getResource(resourcePath);
	// do something with the resource
	// when done, close the ResourceResolver
	resourceResolver.close();
    } catch (LoginException e) {
    	// log the error
    }
}

Within a Servlet

You can access the resource defined by the request URL through the SlingHttpServletRequest:

Resource res = req.getResource();
// req is the SlingHttpServletRequest

You can access any resource by first accessing the ResourceResolver:

String resourcePath = "path/to/resource";
ResourceResolver resourceResolver = req.getResourceResolver();
// req is the SlingHttpServletRequest
Resource res = resourceResolver.getResource(resourcePath);

Within a JSP file

When you use the <sling:defineObjects> tag in a JSP file, you have access to a few handy objects, one of them is resource, the resource that is resolved from the URL. Another one is resourceResolver, the ResourceResolver defined through the SlingHttpServletRequest.

To access a resource:

<sling:defineObjects>
<%
String resourcePath = "path/to/resource";
Resource res = resourceResolver.getResource(resourcePath);
%>

If needed you can adapt a Sling Resource to a JCR Node:

Node node = resource.adaptTo(Node.class);

Note: resource.adaptTo(Node.class) may return null if the resource is not backed by a JCR node. This is particularly the case for NonExistingResource resources or resource provided by a non-JCR resource provider.

Accessing a Property

The ValueMap is an easy way to access properties of a resource. With most resources you can use Adaptable.adaptTo(Class) to adapt the resource to a value map:

ValueMap properties = res.adaptTo(ValueMap.class);
// res is the Resource

You can also access the properties through the ResourceUtil utility class:

ValueMap properties = ResourceUtil.getValueMap(res);
// res is the Resource

Then, to access a specific String property called propName:

String rule = properties.get(propName, (String) null);

For more details about resources and how to access them in Sling, you can refer to the Sling documentation about Resources.