Liferay is an open platform in an ecosystem of open platforms. Just because Liferay has its own MVC framework, therefore, doesn’t mean you have to use it. It is perfectly valid to bring the tools and experience you have from other development projects over to Liferay. In fact, we expect you to. Liferay’s development platform is standards-based, making it an ideal choice for applications of almost any type.

If you’re already a wizard with Spring MVC, you can use it instead of Liferay’s MVCPortlet class with no limitations whatsoever. Since Spring MVC replaces only your application’s web application layer, you can still use Service Builder for your service layer.

So what does it take to implement a Spring MVC application in Liferay? Start by considering how to package a Spring MVC application for Liferay Portal CE 7.0.

Packaging a Spring MVC Portlet

Developers creating portlets for Liferay Portal CE 7.0 can usually deploy their portlet as Java EE-style Web Application ARchive (WAR) artifacts or as Java ARchive (JAR) OSGi bundle artifacts. Spring MVC portlet developers don’t have that flexibility. Spring MVC portlets must be packaged as WAR artifacts because the Spring MVC framework is designed for Java EE. Therefore, it expects a WAR layout and requires Java EE resources such as the WEB-INF/web.xml descriptor.

Because Liferay supports the OSGi WAB standard for deployment, you can deploy your WAR and it will run as expected in the OSGi runtime. Here are the high points on why that works in Liferay Portal CE 7.0:

  • The Liferay auto-deploy process runs, adding the PortletServlet and PlugincontextListener configurations to the WEB-INF/web.xml file.

  • The Liferay WAB Generator automatically creates an OSGi-ready META-INF/MANIFEST.MF file. If you want to affect the content of the manifest file, you can place BND directives and OSGi headers directly into the WEB-INF/liferay-plugin-package.properties file.

You’ll still need to provide the Liferay descriptor files liferay-display.xml and liferay-portlet.xml, and you’ll need a portlet.xml descriptor.

Develop a Spring MVC portlet WAR file with the appropriate descriptor files, and let the auto-deploy process and Liferay’s WAB generator take care of converting your project to a Liferay-ready WAB.

Now get into the details of configuring a Spring MVC portlet for Liferay.

Spring MVC Portlets in Liferay

This isn’t a comprehensive guide to configuring a Spring MVC portlet. It covers the high points, assuming you already have familiarity with Spring MVC. If you don’t, you should consider using Liferay’s MVC framework.

What does a Liferay Spring MVC portlet look like? Almost identical to any other Spring MVC portlet. To configure a Spring MVC portlet, start with the <portlet-class> element in portlet.xml. In it you must declare Spring’s DispatcherPortlet:

<portlet-class>org.springframework.web.portlet.DispatcherPortlet</portlet-class>

The Spring front controller needs to know where the application context file is, so specify it as an initialization parameter in portlet.xml (update the path as needed):

<init-param>
    <name>contextConfigLocation</name>
    <value>/WEB-INF/spring/portlet-context.xml</value>
</init-param>

Provide an application context file (portlet-context.xml in the example above), specified as you normally would for your Spring MVC portlet.

<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix" value="/WEB-INF/views/" />
    <property name="suffix" value=".jsp" />
</bean>

If you’re configuring a WAB yourself, the web.xml file in your Spring MVC project needs to be fully ready for deployment. In addition to any web.xml configuration for Spring MVC, you need to include a listener for PluginContextListener and a servlet and servlet-mapping for PortletServlet:

<listener>
    <listener-class>com.liferay.portal.kernel.servlet.PluginContextListener</listener-class>
</listener>
<servlet>
    <servlet-name>Portlet Servlet</servlet-name>
    <servlet-class>com.liferay.portal.kernel.servlet.PortletServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>Portlet Servlet</servlet-name>
    <url-pattern>/portlet-servlet/*</url-pattern>
</servlet-mapping>

If you’re letting Liferay generate the WAB for you (this is the recommended approach), the above is not necessary, as it is added automatically during auto-deployment.

Your application must be able to convert javax.portlet.PortletRequests to javax.servlet.ServletRequests and back again. Add this to web.xml:

<servlet>
    <servlet-name>ViewRendererServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.ViewRendererServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>ViewRendererServlet</servlet-name>
    <url-pattern>/WEB-INF/servlet/view</url-pattern>
</servlet-mapping>

To configure the Spring view resolver, add a bean in your application context file:

<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix" value="/WEB-INF/views/" />
    <property name="suffix" value=".jsp" />
</bean>

Now the front controller, org.springframework.web.portlet.DispatcherPortlet, can get a request from the view layer, but there are no actual controller classes to delegate the request handling to.

With Spring MVC, your controller is conveniently separated into classes that handle the portlet modes (View, Edit, Help).

You’ll use Spring’s annotations to configure the controller and tell DispatcherPortlet which mode the controller supports.

A simple controller class supporting View mode might look like this:

@Controller("myAppController")
@RequestMapping("VIEW")
public class MyAppController {

    @RenderMapping
    public String processRenderRequest(RenderRequest request,
            RenderResponse response) {

        return "defaultView";
    }
}

The return defaultView statement should be understood in terms of the view resolver bean in the application context file, which gives the String defaultView a prefix of WEB-INF/views/, and a suffix of .jsp. That maps to the path WEB-INF/views/defaultView.jsp, where you would place your default view for the application.

With Spring MVC, you can only support one portlet phase in each controller.

An edit mode controller might contain render methods and action methods.

@Controller("myAppEditController")
@RequestMapping("EDIT")
public class MyAppEditController {

    @RenderMapping
    public String processRenderRequest(RenderRequest request,
            RenderResponse response) {

        return "thisView";
    }

    @ActionMapping(params="action=doSomething")
    public void doSomething(Actionrequest request, ActionResponse response){

        // Do something here

    }
}

You need to define any controller classes in your application context file by adding a <bean> tag for each one:

<bean class="com.liferay.docs.springmvc.portlet.MyAppController" />
<bean class="com.liferay.docs.springmvc.portlet.MyAppEditController" />

Develop your controllers and your views as you normally would in a Spring MVC portlet. You’ll also need to provide some necessary descriptors for Liferay.

Liferay Descriptors

Liferay portlet plugins that are packaged as WAR files should include some Liferay specific descriptors.

The descriptor liferay-display.xml controls the category in which your portlet appears in Liferay Portal’s Add menu. Find the complete DTD here.

Here’s a simple example that just specifies the category the application will go under in Liferay’s menu for adding applications:

<display>
    <category name="New Category">
        <portlet id="example-portlet" />
    </category>
</display>

The descriptor liferay-portlet.xml is used for specifying additional information about the portlet (like the location of CSS and JavaScript files or the portlet’s icon. A complete list of the attributes you can set can be found here

<liferay-portlet-app>
    <portlet>
        <portlet-name>example-portlet</portlet-name>
        <instanceable>true</instanceable>
        <render-weight>0</render-weight>
        <ajaxable>true</ajaxable>
        <header-portlet-css>/css/main.css</header-portlet-css>
        <footer-portlet-javascript>/js/main.js</footer-portlet-javascript>
        <footer-portlet-javascript>/js/jquery.foundation.orbit.js</footer-portlet-javascript>
    </portlet>
    <role-mapper>
        <role-name>administrator</role-name>
        <role-link>Administrator</role-link>
    </role-mapper>
    <role-mapper>
        <role-name>guest</role-name>
        <role-link>Guest</role-link>
    </role-mapper>
    <role-mapper>
        <role-name>power-user</role-name>
        <role-link>Power User</role-link>
    </role-mapper>
    <role-mapper>
        <role-name>user</role-name>
        <role-link>User</role-link>
    </role-mapper>
</liferay-portlet-app>

You’ll also notice the role-mapper elements included above. They’re for defining the Liferay roles used in the portlet.

Then there’s the liferay-plugin-package.properties. These properties describe the Liferay plugin, declare its resources, and specify its security related parameters. The DTD is found here

name=example-portlet
module-group-id=liferay
module-incremental-version=1
tags=
short-description=
change-log=
page-url=http://www.liferay.com
author=Liferay, Inc.
licenses=LGPL
version=1

In the liferay-plugin-package.properties file you can also add OSGi metadata, which is properly placed in the MANIFEST.MF file when you deploy your WAR file.

Find all of Liferay’s DTDs here

Calling Services from Spring MVC

To call OSGi-based Service Builder services from your Spring MVC portlet, you need a mechanism that gives you access to the OSGi service registry.

Since you’re in the context of a Spring MVC portlet, you can’t look up a reference to the services published to the OSGi runtime using Declarative Services. So how do you call Service Builder services, or other services published in the OSGi service registry? One way is by calling the static utility methods.

FooServiceUtil.getFoosByGroupId()

While very simple, that’s not a good way to call OSGi services because of the dynamic nature of the OSGi runtime. Service implementations could be removed and added at any time, and your plugin needs to be able to account for that. Additionally, you need a mechanism that lets your portlet plugin react gracefully to the possibility of the service implementation becoming unavailable entirely. That’s why you should open a Service Tracker when you want to call a service that’s in the OSGi service registry.

Service Trackers

Since you don’t have the luxury of using Declarative Services to manage your service dependencies, you have a little bit of work to do if you want to gain some of the benefits OSGi gives you:

  • Accounting for multiple service implementations, using the best service implementation available (taking into account the service ranking property)

  • Accounting for no service implementations

The static utility classes don’t let you do that, and that’s sad. But be happy, because with a little code, you can regain those benefits. For the details on implementing a service tracker, read the Service Trackers tutorial.

To summarize, you’ll need to do these things:

  • Instantiate a new org.osgi.util.tracker.ServiceTracker to track the service of the type you need.

  • Open the service tracker in an @PostConstruct method.

  • Make sure the service tracker has something in it.

  • If there is indeed something in the service tracker, get the service.

  • Now you’re ready to call the service. Here’s what the if block might look like:

    if (!someServiceTracker.isEmpty()) {
        SomeService someService = someServiceTracker.getService();
        someService.doSomethingCool();
    }
    
  • Close the service tracker in an @PreDestroy method.

That’s probably not enough detail, so refer to the tutorial on Service Trackers for the details. As you’ll see in the tutorial, there’s some boilerplate code involved, but leveraging service trackers lets you look up services in the OSGi runtime.

If you are not required to use a Spring MVC portlet, consider using Liferay’s MVC framework to design your portlets instead. Then you can take advantage of the Declarative Services @Component and @Reference annotations, which let you avoid the boilerplate code associated with service trackers.

Related Topics

Upgrading a Spring MVC Portlet

Using the WAB Generator

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