A Real-World Example Using the Resource API

So far, we’ve covered the basics of ResourceResolver, Resource, and the Resource API.
We’ve seen how to get a resource, access its properties, traverse children, and adapt it to other objects.

But theory is one thing. Let’s see how all this works in a real-world scenario.

1. Requirement

We have a DAM folder /content/dam/my-project-site/documents where we upload a lot of files.
We want to expose an endpoint (a simple servlet) that returns a list of all PDFs uploaded inside that folder, including PDFs in any nested subfolders.

But we don’t want it hardcoded for just one folder.

I want to know what PDFs exist in a certain folder and subfolder—maybe for debugging or to feed another system.

The folder path should be dynamic, passed as a query parameter, so we can check different folders without changing code.

We’ll solve this using pure Resource API.

2. Approach

Before jumping into code, let’s plan it step by step

• We’ll write a Sling Servlet exposed at /bin/list-pdfs
• The servlet will accept a path parameter to specify which folder to search in
• The servlet will use request.getResourceResolver()

Tip: We’re using the request’s ResourceResolver, so no service user or permissions setup is needed — this works only for authenticated users who have access to the given DAM path.

• We’ll fetch the folder as a Resource using getResource(folderPath)
• We’ll use a recursive function to traverse all child folders (not just direct children)
• Inside each folder, we’ll check for dam:Asset resources
• We’ll filter only PDFs (by checking mimeType)
• And finally, print the PDF paths in the response

3. Implementation

So, with that plan in mind, I started coding the servlet.

Here’s the code I wrote first

package com.debug.code.core.servlets;

import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.SlingHttpServletResponse;
import org.apache.sling.api.resource.*;
import org.apache.sling.api.servlets.SlingAllMethodsServlet;
import org.osgi.service.component.annotations.Component;

import javax.servlet.Servlet;
import java.io.IOException;
import java.util.Iterator;

@Component(service = Servlet.class, property = {
        "sling.servlet.paths=/bin/list-pdfs"
})
public class ListPdfAssetsServlet extends SlingAllMethodsServlet {

    @Override
    protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response) throws IOException {
        ResourceResolver resourceResolver = request.getResourceResolver();

        String folderPath = request.getParameter("path");
        if (folderPath == null || folderPath.isEmpty()) {
            response.getWriter().println("Please provide a valid folder path using ?path= parameter.");
            return;
        }

        Resource damFolder = resourceResolver.getResource(folderPath);

        if (damFolder != null) {
            response.setContentType("text/plain");
            listPdfsRecursively(damFolder, response);
        } else {
            response.getWriter().println("Folder not found at path: " + folderPath);
        }
    }

    private void listPdfsRecursively(Resource folder, SlingHttpServletResponse response) throws IOException {
        Iterator<Resource> children = folder.listChildren();

        while (children.hasNext()) {
            Resource child = children.next();

            if (child.isResourceType("dam:Asset")) {
                Resource metadata = child.getChild("jcr:content/metadata");
                if (metadata != null) {
                    ValueMap properties = metadata.getValueMap();
                    String mimeType = properties.get("dc:format", String.class);

                    if ("application/pdf".equals(mimeType)) {
                        response.getWriter().println("PDF: " + child.getPath());
                    }
                }
            } else if (child.isResourceType("sling:OrderedFolder") || child.isResourceType("sling:Folder")) {
                listPdfsRecursively(child, response);
            }
        }
    }
}

4. Code walkthrough

We define a Sling Servlet exposed at /bin/list-pdfs

@Component(service = Servlet.class, property = {
    "sling.servlet.paths=/bin/list-pdfs"
})

This makes the servlet accessible at /bin/list-pdfs without registering under a resource type.

In doGet()We get the folder path from the query param

String folderPath = request.getParameter("path");

We check if it’s missing and send an error message if so.

We get the resource for that folder

Resource damFolder = resourceResolver.getResource(folderPath);

If it doesn’t exist, we return an error. Otherwise, we start recursive traversal.

We traverse recursively

private void listPdfsRecursively(Resource folder, SlingHttpServletResponse response) throws IOException { ... }

Inside this method
For each child

• If it’s dam:Asset, check dc:format (MIME type)
• If it’s a folder, recursively call listPdfsRecursively()

mvn clean install -PautoInstallBundle

mvn clean install -PautoInstallBundle -DskipTests=true

6. Example output:

We’re just printing plain text for simplicity. In real apps, you can easily change the response to JSON.

PDF: /content/dam/my-site/documents/report.pdf
PDF: /content/dam/my-site/documents/2024/march/summary.pdf
PDF: /content/dam/my-site/documents/2024/april/plan.pdf

Every great discussion starts with a simple thought! If you enjoyed this article, found it useful, or have any questions, let’s talk! I’d love to hear from you.

For more updates, tips, and engaging conversations, connect with me on Medium, LinkedIn, and RealCodeWorks. Let’s keep learning together! 🚀✨

Thank you 🙏 !