MVC Resource Command

When using Liferay’s MVCPortlet framework, you can create resource URLs in your JSPs to retrieve images, XML, or any other kind of resource from a Liferay DXP instance. The resource URL then invokes the corresponding MVC resource command class (*MVCResourceCommand) that processes the resource request and response.

Here how to create your own MVC Resource Command:

1. Configure your JSPs to generate resource URLs via <portlet:resourceURL> tags.

   For example, this resource-command-portlet sample resource URL invokes an MVC resource command named /blade/captcha.

   <portlet:resourceURL id="/blade/captcha" var="captchaURL" />
   

2. Name the resource URL via its id attribute.

3. Assign the resource URL’s var attribute a variable name to pass to a UI component.

4. Assign the resource URL variable (var) to a UI component, such as a button or icon. When the user triggers the UI component, the *MVCResourceCommand class that matches the resource URL handles the resource request.

   For example, the sample’s resource URL is triggered when the user clicks on this liferay-captcha component:

   <liferay-captcha:captcha url="<%= captchaURL %>" />
   

5. Create a class that implements the MVCResourceCommand interface, or that extends the BaseMVCResourceCommand class. The latter may save you time, since it already implements MVCResourceCommand.

   Tip: Naming your *MVCResourceCommand class after the resource it provides makes the resource mappings more obvious for maintaining the code. For example, if your resource URL serves a captcha, you could name its class CaptchaMVCResourceCommand. If your application has several MVC command classes, naming them this way helps differentiate them.

6. Annotate your class with an @Component annotation, like this one:

   @Component(
       property = {
           "javax.portlet.name=your_portlet_name_YourPortlet",
           "mvc.command.name=/your/jsp/resource/url"
       },
       service = MVCResourceCommand.class
   )
   public class YourMVCResourceCommand extends BaseMVCResourceCommand {
       // your resource handling code
   }
   

   1. Set a javax.portlet.name property to your portlet’s internal ID.

   2. Set the mvc.command.name property to your <portlet:resourceURL> tag’s id. This maps your class to the resource URL of the same name.

   3. Register your class as an MVCResourceCommand service by setting the service attribute to MVCResourceCommand.class.

7. Implement your resource logic by overriding the appropriate method of the class you’re implementing or extending.

   • MVCResourceCommand implementations override the serveResource method.

   • BaseMVCResourceCommand extensions override the doServeResource method.

For example, the resource-command-portlet’s CaptchaMVCResourceCommand class implements the MVCResourceCommand interface with only a single method: serveResource.

@Component(
	immediate = true,
	property = {
		"javax.portlet.name=com_liferay_blade_samples_portlet_resourcecommand_CaptchaPortlet",
		"mvc.command.name=/blade/captcha"
	},
	service = MVCResourceCommand.class
)
public class CaptchaMVCResourceCommand implements MVCResourceCommand {

	@Override
	public boolean serveResource(
			ResourceRequest resourceRequest, ResourceResponse resourceResponse)
		throws PortletException {

		if (_log.isInfoEnabled()) {
			_log.info("get captcha resource ");
		}

		try {
			CaptchaUtil.serveImage(resourceRequest, resourceResponse);

			return false;
		}
		catch (Exception e) {
			_log.error(e.getMessage(), e);

			return true;
		}
	}

	private static final Log _log = LogFactoryUtil.getLog(
		CaptchaMVCResourceCommand.class);

}

This serveResource method processes the resource request and response via the javax.portlet.ResourceRequest and javax.portlet.ResourceResponse parameters, respectively. Note that the try block uses the helper class CaptchaUtil to serve the CAPTCHA image. Though you don’t have to create such a helper class, doing so often simplifies your code.

Great! Now you know how to use MVCResourceCommand to process resources in your Liferay MVC Portlets.

Related Topics

Creating an MVC Portlet

Configuring the View Layer

MVC Render Command

MVC Action Command

MVC Command Overrides