Leveraging the Script Engine in Workflow

Liferay’s Kaleo workflow engine provides a robust system for reviewing and approving content in an enterprise environment. Even if you don’t leverage custom scripts, it’s a powerful and robust workflow solution. Adding custom scripts takes it to the next level.

The final step in a workflow should run a script that makes content available for use. As you can see in the snippet below, JavaScript can be used to access the Java class associated with the workflow to set the status of the content to approved.

<script>
    <![CDATA[
        Packages.com.liferay.portal.kernel.workflow.WorkflowStatusManagerUtil.updateStatus(Packages.com.liferay.portal.kernel.workflow.WorkflowConstants.toStatus("denied"), workflowContext);
        Packages.com.liferay.portal.kernel.workflow.WorkflowStatusManagerUtil.updateStatus(Packages.com.liferay.portal.kernel.workflow.WorkflowConstants.toStatus("pending"), workflowContext);
    ]]>
</script>
<script-language>javascript</script-language>

At virtually any point in a workflow, you can use Liferay’s script engine to access workflow APIs or other Liferay APIs. There are a lot of different ways you could use this. Here are a few practical examples:

  • Getting a list of users with a specific workflow-related role
  • Sending an email to the designated content approver with a list of people to contact if he is unable to review the content
  • Creating an alert to be displayed in the Alerts portlet for any user assigned to approve content

Of course, before you try any of this, you need to know the appropriate syntax for inserting a script into a workflow. In an XML workflow definition, a script can be used in any XML type that can contain an actions tag: those types are <state>, <task>, <fork> and <join>. Inside of one of those types, format your script like this:

<actions>
    <action>
        <script>
            <![CDATA[*the contents of your script*]]>
        </script>
        <script-language>*your scripting language of choice*</script-language>
    </action>
    ...
</actions>

Here’s an example of a workflow script created in Groovy. This one is designed to be used with a Condition statement in Kaleo. It accesses Liferay’s asset framework to determine the category of an asset in the workflow. The script uses the category to automatically determine the correct approval process. If the category legal has been applied to the asset, the asset is sent to the Legal Review task upon submission. Otherwise, the asset is sent to the Default Review task.

<script>
    <![CDATA[
        import com.liferay.portal.kernel.util.GetterUtil;
        import com.liferay.portal.kernel.workflow.WorkflowConstants;
        import com.liferay.portal.kernel.workflow.WorkflowHandler;
        import com.liferay.portal.kernel.workflow.WorkflowHandlerRegistryUtil;
        import com.liferay.portlet.asset.model.AssetCategory;
        import com.liferay.portlet.asset.model.AssetEntry;
        import com.liferay.portlet.asset.model.AssetRenderer;
        import com.liferay.portlet.asset.model.AssetRendererFactory;
        import com.liferay.portlet.asset.service.AssetEntryLocalServiceUtil;

        import java.util.List;

        String className = (String)workflowContext.get(
            WorkflowConstants.CONTEXT_ENTRY_CLASS_NAME);

        WorkflowHandler workflowHandler =
            WorkflowHandlerRegistryUtil.getWorkflowHandler(className);

        AssetRendererFactory assetRendererFactory =
            workflowHandler.getAssetRendererFactory();

        long classPK =
            GetterUtil.getLong((String)workflowContext.get
            (WorkflowConstants.CONTEXT_ENTRY_CLASS_PK));

        AssetRenderer assetRenderer =
            workflowHandler.getAssetRenderer(classPK);

        AssetEntry assetEntry = assetRendererFactory.getAssetEntry(
            assetRendererFactory.getClassName(), assetRenderer.getClassPK());

        List<AssetCategory> assetCategories = assetEntry.getCategories();

        returnValue = "Default Review";

        for (AssetCategory assetCategory : assetCategories) {
            String categoryName = assetCategory.getName();

            if (categoryName.equals("legal")) {
                returnValue = "Legal Review";

                return;
            }
        }
       ]]>
</script>
<script-language>groovy</script-language>

Within a workflow, the next task or state is chosen based on the return value. For a complete example of a workflow script that uses the above Groovy script, please see this legal-workflow-script.xml file: https://github.com/liferay/liferay-docs/blob/6.2.x/userGuide/code/legal-workflow-script.xml.

Calling OSGi Services

How do you call OSGi services from a workflow script, accounting for the dynamic environment of the OSGi runtime, where services your script depends on can disappear without notice? Use a service tracker. That way you can check to make sure your code has access to the service it needs, and if not, do something appropriate in response. Here’s a little example code to show you how this might look in Groovy (import statements excluded):

ServiceTracker<SomeLocalService,SomeLocalService> st;

try {
    Bundle bundle = FrameworkUtil.getBundle(GroovyExecutor.class);

    st = new ServiceTracker(bundle.getBundleContext(), JournalArticleLocalService.class, null);
    st.open();

    if (!st.isEmpty()) {
        SomeLocalService _SomeLocalService = st.getService();

        //Do cool stuff with the service you retrieved
    }
}
catch(Exception e) {
    //Handle error appropriately
}
finally {
    if (st != null) {
        st.close();
    }
}

If you read the article on service trackers, the only odd looking piece of the above code is the getBundle call: why is GroovyExecutor.class passed as a parameter? The parameter passed to the FrameworkUtil.getBundle call must be a class from the bundle executing the workflow script. This is different from the context of a plugin project, where you’d want to get the bundle hosting the class where you’re making the call (using this.getClass(), for example). Note that for another scripting engine, you must pass in a concrete class from the particular bundle executing your script.

The combination of Liferay’s script and workflow engines is incredibly powerful. However, since it provides users with the ability to execute code, it can be dangerous. When configuring your permissions, be aware of the potential consequences of poorly or maliciously written scripts inside of a workflow definition. For more information on creating workflow definitions with Kaleo workflow, see Liferay DXP’s workflow documentation.

Invoking Liferay Services From Scripts

Running Scripts From the Script Console

Using Liferay’s Script Engine

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