MVC Render Command

If you’re here, that means you know that MVCRenderCommands are used to respond to portlet render URLs, and you want to know how to create and use MVC render commands. If you just want to learn about Liferay’s MVC Portlet framework in general, that information is in a separate article.

To use MVC render commands, you need these things:

• An implementation of the MVCRenderCommand interface.
• A portlet render URL in your view layer.
• a Component that publishes the MVCRenderCommand service, with two properties.

Implementing MVCRenderCommand

What is it you want to do when a portlet render URL is invoked? Using the mvcRenderCommandName parameter, direct the request to an MVCRenderCommand implementation. Now override the render method.

Some MVCRenderCommands will simply render a particular JSP. Here’s what BlogsViewMVCRenderCommand looks like:

@Override
public String render(
	RenderRequest renderRequest, RenderResponse renderResponse) {

	return "/blogs/view.jsp";
}

Sometimes you’ll want to add logic to render a certain JSP based on one or more conditions:

@Override
public String render(
    RenderRequest renderRequest, RenderResponse renderResponse)
    throws PortletException {

    try {
        ActionUtil.getEntry(renderRequest);
    }
    catch (Exception e) {
        if (e instanceof NoSuchEntryException ||
            e instanceof PrincipalException) {

            SessionErrors.add(renderRequest, e.getClass());

            return "/hello/error.jsp";
        }
        else {
            throw new PortletException(e);
        }
    }

    return "/hello/edit_entry.jsp";
}

If there’s an error caught following the call to ActionUtil.getEntry in the code above, the error.jsp is rendered. If the call is returned without an exception being caught, edit_entry.jsp is rendered.

How does a request get directed to your MVC render command? Using a portlet render URL.

Creating a Portlet Render URL

You can generate a render URL for your portlet using the <portlet:renderURL> taglib. To invoke your MVC render command from the render URL, you need to specify the parameter mvcRenderCommandName with the same value as your Component property mvc.command.name.

For example, you can create a URL that directs the user to a page with a form for editing an entry like this (in a JSP):

<portlet:renderURL var="editEntryURL">
    <portlet:param name="mvcRenderCommandName" value="/hello/edit_entry" />
    <portlet:param name="entryId" value="<%= String.valueOf(entry.getEntryId()) %>" />
</portlet:renderURL>

Now the request will contain a parameter named mvcRenderCommandName. To find the proper MVC render command, the OSGi runtime needs to have a mvc.command.name property with a matching value.

Registering the MVC Render Command

In order to respond to a particular render URL, you need an MVCRenderCommand Component that with two properties:

 "javax.portlet.name=" + HelloWorldPortletKeys.HELLO_WORLD,
 "mvc.command.name=/hello/edit_entry"

Using the above properties as an example, any portlet render URL for the portlet that includes a parameter called mvcRenderCommand with the value /hello/edit_entry will be handled by this MVCRenderCommand.

The Component must also publish a MVCRenderCommand.class service to the OSGi runtime. Here’s a basic Component that publishes an MVC render command.

@Component(
    immediate = true,
    property = {
       "javax.portlet.name=" + HelloWorldPortletKeys.HELLO_WORLD,
       "mvc.command.name=/hello/edit_entry"
    },
    service = MVCRenderCommand.class
)
public class EditEntryMVCRenderCommand implements MVCRenderCommand {

One command can be used by one portlet, as the example above shows. If you want, one command can be used for multiple portlets by adding more javax.portlet.name entries in the property list. Likewise, multiple commands can invoke the MVC command class by adding more mvc.command.name entries. If you’re really feeling wild, you can specify multiple portlets and multiple command URLs in the same command component, like this:

@Component(
    immediate = true,
    property = {
       "javax.portlet.name=" + HelloWorldPortletKeys.HELLO_MY_WORLD,
       "javax.portlet.name=" + HelloWorldPortletKeys.HELLO_WORLD,
       "mvc.command.name=/hello/edit_super_entry",
       "mvc.command.name=/hello/edit_entry"
    },
    service = MVCRenderCommand.class
)

As you can see, MVC render commands are flexible and very easy to implement.

Related Topics

MVC Resource Command

MVC Action Command

MVC Command Overrides