How to customize Participant Step dialog with dynamic checkbox values from workflow metadata?

Hey ​@EddieHuang , The standard Participant Step dialog configuration does not support dynamic fields driven by workflow metadata out of the box. You'll need a combination of:

1. A custom dialog resource with a dynamic Granite UI datasource

2. A custom servlet to read workflow metadata and feed it to the dialog

3. Standard workflow metadata persistence on dialog completion

Step-by-Step Approach:

1. Create a Custom Dialog Step 

In your workflow model, instead of using the default Participant Step dialog, define a custom Dialog Participant Step that points to a custom dialog path.

In the workflow model node (under 

/var/workflow/models/your-model

), configure the Dialog Participant Step with:

dialogPath = /apps/your-project/workflow/dialogs/select-nodes

2. Create the Custom Dialog Resource

Create a Granite UI dialog at 

/apps/your-project/workflow/dialogs/select-nodes

:

<?xml version="1.0" encoding="UTF-8"?>
<jcr:root xmlns:jcr="http://www.jcp.org/jcr/1.0"
          xmlns:sling="http://sling.apache.org/jcr/sling/1.0"
          xmlns:granite="http://www.adobe.com/jcr/granite/1.0"
          jcr:primaryType="nt:unstructured"
          jcr:title="Select Nodes to Publish"
          sling:resourceType="cq/gui/components/common/admin/dialog">
    <content jcr:primaryType="nt:unstructured"
             sling:resourceType="granite/ui/components/coral/foundation/container">
        <items jcr:primaryType="nt:unstructured">
            <nodePaths jcr:primaryType="nt:unstructured"
                       sling:resourceType="granite/ui/components/coral/foundation/form/checkboxgroup"
                       fieldLabel="Discovered Nodes"
                       name="selectedNodePaths">
                <datasource jcr:primaryType="nt:unstructured"
                            sling:resourceType="your-project/datasources/workflow-nodes"/>
            </nodePaths>
        </items>
    </content>
</jcr:root>

The key here is the 

datasource

 — it points to a custom Sling resource type that dynamically generates checkbox items.

3. Create the Datasource Servlet

This servlet reads 

discoveredNodePaths

 from workflow metadata and returns them as checkbox options:

package com.yourproject.core.servlets;

import com.adobe.granite.ui.components.ds.DataSource;
import com.adobe.granite.ui.components.ds.SimpleDataSource;
import com.adobe.granite.ui.components.ds.ValueMapResource;
import com.adobe.granite.workflow.WorkflowSession;
import com.adobe.granite.workflow.exec.WorkItem;
import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.SlingHttpServletResponse;
import org.apache.sling.api.resource.ResourceMetadata;
import org.apache.sling.api.resource.ValueMap;
import org.apache.sling.api.servlets.SlingSafeMethodServlet;
import org.apache.sling.api.wrappers.ValueMapDecorator;
import org.osgi.service.component.annotations.Component;

import javax.servlet.Servlet;
import java.util.*;

import static org.apache.sling.api.servlets.ServletResolverConstants.*;

@Component(service = Servlet.class, property = {
    SLING_SERVLET_RESOURCE_TYPES + "=your-project/datasources/workflow-nodes",
    SLING_SERVLET_METHODS + "=GET"
})
public class WorkflowNodesDatasourceServlet extends SlingSafeMethodServlet {

    @Override
    protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response) {
        List<com.adobe.granite.ui.components.ds.ValueMapResource> items = new ArrayList<>();

        try {
// Extract workitem ID from request (AEM passes this as a parameter)
            String workItemId = request.getParameter("workitem");
            if (workItemId != null) {
                WorkflowSession wfSession = request.getResourceResolver()
                    .adaptTo(WorkflowSession.class);
                WorkItem workItem = wfSession.getWorkItem(workItemId);
                String[] paths = (String[]) workItem.getWorkflow()
                    .getWorkflowData().getMetaDataMap().get("discoveredNodePaths");

                if (paths != null) {
                    for (String path : paths) {
                        ValueMap vm = new ValueMapDecorator(new HashMap<>());
                        vm.put("value", path);
                        vm.put("text", path);
                        items.add(new ValueMapResource(
                            request.getResourceResolver(),
                            new ResourceMetadata(),
                            "nt:unstructured",
                            vm));
                    }
                }
            }
        } catch (Exception e) {
// log error
        }

        request.setAttribute(DataSource.class.getName(),
            new SimpleDataSource(items.iterator()));
    }
}

4. Persisting Selected Values Back to Metadata

AEM handles this automatically for Dialog Participant Steps. When the editor clicks "Complete" in the Inbox, all form field values from the dialog are stored in the work item's metadata map.

To access the selected values in a subsequent Process Step:

@Override
public void execute(WorkItem workItem, WorkflowSession wfSession, MetaDataMap args) {
// Dialog field values are stored in the workitem metadata
    String[] selectedPaths = (String[]) workItem.getWorkflow()
        .getWorkflowData().getMetaDataMap().get("selectedNodePaths");

// Or from the work item's own metadata
    MetaDataMap wfMeta = workItem.getMetaDataMap();
    String selectedRaw = wfMeta.get("selectedNodePaths", String.class);
}

Important caveat: Dialog Participant Step stores form values in the 

WorkItem

 metadata, not the 

WorkflowData

 metadata. If you need them in 

WorkflowData

 metadata for downstream steps, add a small Process Step after the dialog step that copies values:

Key Considerations for AEMaaCS

• Dialog Participant Step is the correct step type — not a plain Participant Step. It supports custom 

  dialogPath

  .

• The 

  workitem

   request parameter availability in the datasource servlet depends on how AEM's Inbox UI renders the dialog. You may need to inspect the Inbox network calls to confirm the exact parameter name (it could be 

  item

   or 

  taskId

   in newer AEM versions).

• If the datasource servlet cannot reliably get the work item ID from the dialog request, an alternative is to use a custom Granite UI clientlib that fetches metadata via a separate Sling servlet (AJAX call) and populates the checkboxes client-side.

• For AEMaaCS, ensure your servlet and dialog resources are deployed via your 

  ui.apps

   module.

Folder Structure

The datasource 

.content.xml

 is minimal:

<jcr:root xmlns:jcr="http://www.jcp.org/jcr/1.0"
          xmlns:sling="http://sling.apache.org/jcr/sling/1.0"
          jcr:primaryType="nt:unstructured"
          sling:resourceType="your-project/datasources/workflow-nodes"/>

This approach keeps everything within standard AEM patterns — no custom Inbox UI extensions needed.