<p>Sling assumes everything is a resource, so it's important for AEM developers to understand what resources are and how to work with them. In this post, I try to cover the basics and provide an overview for developers who are new to AEM.</p>
<p>To begin, it's helpful to know that Sling maintains a <em>virtual tree</em> of resources (e.g. pages, users, components, etc.). This <em>virtual tree </em>is a merger of contents (i.e. resources) that are made available by resource providers. Resource providers allow access to resources from the JCR Repository and other locations such as databases or bundles.&nbsp;</p>
<h3>Resource Providers</h3>
<p>A resource provider allows access to a resource. The main resource provider is the <em>JcrResourceProvider,</em> it supports Node and Property based resources. Each resource provider is registered as an OSGi service and contains a required property called <code>provider.roots</code>. The property value specifies a path within the tree for which the resource provider should be used. For example, let's assume multiple resource providers have been registered. One of the resource providers contains a <code>provider.roots</code> property value of <code>/subtree/path</code>. When a request to access a resource at <code>/subtree/path/my-resource</code> is made, then this resource provider would receive the request before the others because it's <code>provider.roots</code> has the closest match to the path of the resource.</p>
<h3>Resource Resolver</h3>
<p>The ResourceResolver is responsible for applying a "longest prefix matching algorithm" to find the best matching resource provider for a given resource. Once a resource object is resolved, the ResourceResolver's defined API can be used to do work such as editing or updating the resource.&nbsp;</p>
<p>There are two ways to obtain a ResourceResolver:</p>
<ol>
<li>A resource resolver is available to the request processing servlet</li>
<li>A resource resolver can be created with the <a href="https://sling.apache.org/apidocs/sling11/org/apache/sling/api/resource/ResourceResolver.html">ResourceResolverFactoryService</a></li>
</ol>
<p>Below is psudo code showing how to obtain the resource resolver for each approach.&nbsp;</p>
<h3>ResourceResolver via Request</h3>
<p>The code below assumes you are working with Sling Models, the resolver will have the same permissions as the user making the request.</p>
<pre class="language-java"><code>@Model(adaptables = SlingHttpServletRequest.class)
public class MySlingModel {

    @SlingObject
    private ResourceResolver resourceResolver;

    @PostConstruct
    public void init() {
       ...
    }
}</code></pre>
<h3>ResourceResolver via ResourceResolverFactory</h3>
<p>In the example Sling Model above, the resource resolver was obtained from the request. I did not open it and therefore, do not need to close it.&nbsp;</p>
<p>Below is the AutoCloseable resource resolver syntax.&nbsp; The resource resolver is explicity created and would be required to close if not for the <a title="Java try-with-resource documentation" href="https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html" target="_blank" rel="noopener">try-with-resource</a> syntax.&nbsp;&nbsp;</p>
<pre class="language-java"><code>try (ResourceResolver resolver = resourceResolverFactory.getServiceResourceResolver(&hellip;)) {
  ...
}</code></pre>
<p><br />In the final code example, the resource resolver is opened and needs to closed explicitly. The code below assumes that you have created the WriteService interface and defined a service user with appropriate permissions for your needs (Review the <a title="RepoInit" href="../blog/aem-repository-initialization-with-repoinit" target="_blank" rel="noopener">RepoInit</a> post if you have not already).</p>
<pre class="language-java"><code>@Component(immediate = true, service = WriteService.class)
public class WriteServiceImpl implements WriteService {

    @Reference
    ResourceResolverFactory resolverFactory;

    @Override
    public ResourceResolver getResourceResolverObject() throws LoginException {
        Map&lt;String, Object&gt; param = new HashMap&lt;&gt;();
        param.put(ResourceResolverFactory.SUBSERVICE, "WriteService");
        ResourceResolver resolver;

        resolver = resolverFactory.getServiceResourceResolver(param);
        return resolver;
    }
}</code></pre>
<p>&nbsp;</p>
<p>The WriteService can be imported and used to retrieve the Resource Resolver in other classes.</p>
<pre class="language-java"><code>ResourceResolver resolver = writeService.getResourceResolverObject();</code></pre>
<p>&nbsp;</p>
<p>Remember to close the resolver when your work is done.</p>
<pre class="language-java"><code>resolver.close();</code></pre>

Sling assumes everything is a resource, so it's important for AEM developers to understand what resources are and how to work with them. In this post, I try to cover the basics and provide an overview for developers who are new to AEM.