Overriding MVCRenderCommands

You can override MVCRenderCommand for any portlet that uses Liferay’s MVC framework and publishes an MVCRenderCommand component.

For example, Liferay’s Blogs application has a class called EditEntryMVCRenderCommand, with this component:

@Component(
    immediate = true,
    property = {
        "javax.portlet.name=" + BlogsPortletKeys.BLOGS,
        "javax.portlet.name=" + BlogsPortletKeys.BLOGS_ADMIN,
        "javax.portlet.name=" + BlogsPortletKeys.BLOGS_AGGREGATOR,
        "mvc.command.name=/blogs/edit_entry"
    },
    service = MVCRenderCommand.class
)

This MVC render command can be invoked from any of the portlets specified by the javax.portlet.name parameter, by calling a render URL that names the MVC command.

<portlet:renderURL var="addEntryURL">
	<portlet:param name="mvcRenderCommandName" value="/blogs/edit_entry" />
	<portlet:param name="redirect" value="<%= viewEntriesURL %>" />
</portlet:renderURL>

What if you want to override the command, but not for all of the portlets listed in the original component? In your override component, just list the javax.portlet.name of the portlets where you want the override to take effect. For example, if you want to override the /blogs/edit_entry MVC render command just for the Blogs Admin portlet (the Blogs Application accessed in the site administration section of Liferay), your component could look like this:

@Component(
  immediate = true,
  property = {
     "javax.portlet.name=" + BlogsPortletKeys.BLOGS_ADMIN,
     "mvc.command.name=/blogs/edit_entry",
     "service.ranking:Integer=100"
  },
  service = MVCRenderCommand.class
)

Note the last property listed, service.ranking. It’s used to tell the OSGi runtime which service to use, in cases where there are multiple components registering the same service, with the same properties. The higher the integer you specify here, the more weight your component carries. In this case, the override component is used instead of the original one, since the default value for this property is 0.

After that, it’s up to you to do whatever you’d like. MVC render commands can be customized for these purposes:

Adding Logic to an Existing MVC Render Command
Redirecting to a new JSP

Start by exploring how to add logic to an existing MVC render command.

Adding Logic to an Existing MVC Render Command

You can add logic to an MVC render command following the general steps for MVC commands. Specifically for MVC render commands, you must directly implement the MVCRenderCommand interface and override its render method.

For example, this custom MVC render command has a placeholder (i.e., at comment //Do something here) for adding logic to the render method.:

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

        //Do something here

		return mvcRenderCommand.render(renderRequest, renderResponse);
	}

    @Reference(target = 
          "(component.name=com.liferay.blogs.web.internal.portlet.action.EditEntryMVCRenderCommand)")
      protected MVCRenderCommand mvcRenderCommand;
}

The example references an EditEntryMVCRenderCommand implementation of MVCRenderCommand. In the render method, you’d replace the placeholder with new logic and then invoke the original implementation’s logic by calling its render method.

Sometimes, you might need to redirect the request to an entirely new JSP. You can do that from a custom MVC render command module too.

Redirecting to a New JSP

MVCRenderCommand’s render method returns a JSP path as a String. By default, the JSP must live in the original module, so you cannot simply specify a path to a custom JSP in your override module. To redirect it to a JSP in your new module, you must make the method skip dispatching to the original JSP altogether, by using the constant MVCRenderConstants.MVC_PATH_VALUE_SKIP_DISPATCH class. Then you need to initiate your own dispatching process, directing the request to your JSP path. Here’s how that might look in practice:

public class CustomEditEntryMVCRenderCommand implements MVCRenderCommand {

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

        System.out.println("Rendering custom_edit_entry.jsp");

        RequestDispatcher requestDispatcher =
            servletContext.getRequestDispatcher("/custom_edit_entry.jsp");

        try {
            HttpServletRequest httpServletRequest = 
                PortalUtil.getHttpServletRequest(renderRequest);
            HttpServletResponse httpServletResponse = 
                PortalUtil.getHttpServletResponse(renderResponse);

            requestDispatcher.include
                (httpServletRequest, httpServletResponse);
        } catch (Exception e) {
            throw new PortletException
                ("Unable to include custom_edit_entry.jsp", e);
        }

        return MVCRenderConstants.MVC_PATH_VALUE_SKIP_DISPATCH;
    }

    @Reference(target = "(osgi.web.symbolicname=com.custom.code.web)")
    protected ServletContext servletContext;
}

The servlet context provides access to the request dispatcher. A servlet context is automatically created for portlets. It can be created for other modules by including the following line in your bnd.bnd file:

Web-ContextPath: /custom-code-web

Follow these steps to fetch the portlet’s servlet context in your custom MVC render command:

Add a ServletContext field.

protected ServletContext servletContext;

Add the @Reference annotation to the field and set the annotation to filter on the portlet’s module. By convention, Liferay puts portlets in modules whose symbolic names end in .web. For example, this servlet context reference filters on a module whose symbolic name is com.custom.code.web.
```
@Reference(target = "(osgi.web.symbolicname=com.custom.code.web)")
protected ServletContext servletContext;
```

Implement your render method this way:

Get a request dispatcher to your module’s custom JSP.

RequestDispatcher requestDispatcher =
    servletContext.getRequestDispatcher("/custom_edit_entry.jsp");

Include the HTTP servlet request and response in the request dispatcher.

try {
    HttpServletRequest httpServletRequest = 
        PortalUtil.getHttpServletRequest(renderRequest);
    HttpServletResponse httpServletResponse = 
        PortalUtil.getHttpServletResponse(renderResponse);

    requestDispatcher.include
        (httpServletRequest, httpServletResponse);
} catch (Exception e) {
    throw new PortletException
        ("Unable to include custom_edit_entry.jsp", e);
}