Liferay as a Development Platform

If you’ve been reading everything up to this point, you’ve heard all about Liferay Portal’s architecture, modularity, and technologies. What’s left is to tell you what it’s like to use Liferay’s platform as a basis for your site by customizing it or by developing applications on it. The platform is designed to make this easy and pleasant, and to integrate with the tools developers use every day.

But you’re likely not interested in a bunch of prolegomena about it. Read on to learn the details.

Web Applications and Portlets

Liferay as a development platform has always provided flexibility for both administrators and developers by making it easy to have more than one application on a single page. Applications written this way are called portlets, and are a mainstay of Liferay’s platform. You can use Liferay’s MVC Portlet framework or common frameworks such as Spring MVC or JSF to write portlets. If you plan to have a web-based interface to your application, and want its administrator to have a lot of flexibility configuring it, portlets provide a very powerful model. In this model you can create several portlets instead of a larger application and let the administrator choose how to combine them with other pre-existing portlets into a larger interface.

That’s not to say you don’t have other choices. Since Liferay decouples its business logic from its UI (which is provided in separate modules), you have freedom to implement the UI in any other technology.

Because of this, you can use Liferay as a headless platform, because it’s easy to create web services based on Service Builder, JAX-RS, and JAX-WS. Then you can build standalone web applications using any front-end technology or mobile technology you like.

Extensibility

As you might imagine, the system described above contains all the tools necessary to make a well designed system that allows developers not only to create applications based on modules, but also to extend the existing functionality of the system. Liferay can benefit from this now because the platform on which it rests is designed for both application development and customization.

Components make developing extensions and customizations convenient. If you compare this model to other products that aren’t designed for customization, you’ll see just how convenient it can be.

To customize an existing service, the only thing you need to do is deploy a component that extends the existing implementation. If you want to remove your implementation and revert back to the default behavior, you simply un-deploy your component.

Compare that with the traditional way of customizing software by downloading its source and maintaining a set of patches against it. Each time the software is updated, you have to re-download the source, re-apply your patches, and recompile the software.

With Liferay, your custom code is kept in your own modules, which the container takes care of applying based on metadata you supply.

Developer Tools

As you learned above, Liferay’s OSGi container gives you these benefits:

  • The container can start and stop components.
  • A component implements an OSGi service.
  • A component may use or consume OSGi services.
  • The framework manages the binding of the services a component consumes (just like Spring or EJBs, but dynamically).

If all of this sounds great to you (as it does to us), there’s only one thing left: how do you get started developing components? We believe in providing an easy path for new developers while at the same time preserving flexibility for experienced developers with strong tooling preferences. To achieve that, Liferay provides some great tools, and if you’re an experienced developer, these also integrate into what you likely already use. If you use any of the standard build tools like Gradle or Maven, any text editor or common Java IDEs like Eclipse, intelliJ, or NetBeans, or any testing framework like Spock or JUnit, you can use them with Liferay to develop components.

Liferay’s tools add some important enhancements:

  • Blade CLI speeds you up by creating Gradle-based Liferay projects from templates.
  • Liferay Workspace is an opinionated SDK based on Gradle that uses Blade CLI to integrate your projects and your runtime into one convenient, distributable and sharable place.
  • Liferay IDE is an Eclipse-based development environment that integrates all the convenience of Blade CLI and Liferay Workspace into a best-of-breed graphical environment with all the bells and whistles you’d expect.
  • Liferay Developer Studio provides all that Liferay IDE provides, plus additional tools that enterprise developers need.
  • Liferay Service Builder helps you create your back-end faster by generating all your database tables, local services, and web services from a single XML file.

You can choose to use or ignore Liferay’s tools. The point is you have the freedom to do that, because Liferay provides an open development framework that’s designed to meet you where you are. We hate proprietary lock-in as much as you do, so our tools are designed to complement the tools you’re using already instead of replacing them.

Beyond build tools and IDEs are the frameworks you’ll use to build applications. Liferay’s development frameworks include a lot of functionality–comments, social relationships, user management, and lots more–to speed up development of your applications. They help you build applications out of well-tested, modern, scalable, skinnable building blocks. You wind up not only with a great, functional application, but also with one that took less time to develop, looks the way you want it to, and performs well. This doesn’t mean you’re limited only to what Liferay provides; again, you can use third-party frameworks if that’s what you like to use.

To develop portlets, Liferay provides a convenient and easy-to-use framework called MVCPortlet to make writing portlets easy, but developers are free to use any other framework, such as Spring MVC, to create portlets. MVCPortlet uses components to handle requests, benefiting from all the characteristics described above (lifecycle, extensibility, ease of composition, etc.). If you don’t have a strong opinion on which framework to use, we recommend that you try it out.

Liferay also includes a utility called Service Builder that makes it easy to create back-end database tables, an object-relational map in Java for accessing them, and a place to put your business logic. It can also generate JSON or SOAP web services, giving developers a full stack for storing and retrieving data using web or mobile clients. But that doesn’t prevent you from using Java Persistence (JPA) and generating JAX-WS web services.

In addition to the tooling, Liferay also provides many reusable frameworks.

Frameworks and APIs

Liferay’s development platform provides a great framework for application development and also offers APIs. Lots of them. Applications can be created by leveraging Liferay’s many frameworks that encapsulate features that are commonly needed by today’s applications. For example, a commenting system allows developers to attach comments to any asset that they define, whether they be assets they develop or assets that ship with the system. Assets are shared by the system and are used to represent many common elements, such as Users, Organizations, Sites, User Groups, blog entries, and even folders and files.

Liferay also includes many frameworks for operating on assets. A workflow system makes it easy to create applications that require an approval process for users to follow. The recycle bin stores deleted assets for a specified period of time, making it easy for users to restore data without the intervention of an administrator. A file storage API with multiple available back-ends makes storing and sharing files trivial. Search is built into the system as well, and it is designed for developers to integrate it with their applications. Many of the frameworks you might need when developing complex applications are already there; you just need to take advantage of them: a Social Networking API, user-generated forms with data lists, a message bus, an audit system, and much more.

Example Liferay Projects

Enough theory. It’s time for practice. A good way to get the flavor of developing on Liferay’s platform across is to show you some projects. First, you’ll see a portlet developed with MVCPortlet, showcasing the use of components as well. Once you’ve seen that, the next best thing is to see an extension. Both of these examples serve to show you how easy it is to build functionality following a modular paradigm.

It would be nice to show you the standard Hello World project, Liferay style, but that would be too easy: the default template that Blade or Liferay IDE creates already does that by default. Instead, you’ll see the Hello You portlet. This does the same thing as Hello World, except it adds the first name of the user to the message. If your name therefore is John, it’ll return Hello, John.

Here’s what the project layout looks like:

hello-you-portlet-layout.png

The Hello You portlet has a simple project structure.

No new files were created after this project was generated by Liferay’s Blade CLI tool, so this is as simple as it gets. You have your portlet class, which is in the .java file. You also have two different kinds of resources: language properties and JSP files. Finally, the bnd.bnd file describes the application’s metadata for the OSGi container, and the build.gradle file builds the project.

Any web developer that’s familiar with Java can understand the JSPs, but some explanation is in order because of the style. Liferay’s coding style defines a single init.jsp that contains all the imports and tag library initializations necessary for the front-end. This way, any JSP can simply include init.jsp, and all of its imports are satisfied. The init.jsp for this project was not modified from the generated project, and it looks like this:

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

<%@ taglib uri="http://java.sun.com/portlet\_2\_0" prefix="portlet" %>

<%@ taglib uri="http://liferay.com/tld/aui" prefix="aui" %>

<%@ taglib uri="http://liferay.com/tld/portlet" prefix="liferay-portlet" %>

<%@ taglib uri="http://liferay.com/tld/theme" prefix="liferay-theme" %>

<%@ taglib uri="http://liferay.com/tld/ui" prefix="liferay-ui" %>

<liferay-theme:defineObjects />

<portlet:defineObjects />

As you can see, all it does is declare the tag libraries you probably want to use, and then it calls a couple of tags that makes objects from the portlet framework available. Since there’s nothing really interesting here, you’ll want to look at view.jsp next:

<%@ include file="/init.jsp" %>

<jsp:useBean id="userName" type="java.lang.String" scope="request" />

<p>

    <b>Hello, <%=userName %>!</b>

</p>

Now we’ve got something. The portlet class (the Controller, in MVC terms) has made a userName string available in the request, and this JSP retrieves it and uses it to say hello to the user. The real functionality, therefore is in the portlet class:

@Component(
    immediate = true,
    property = {
        "com.liferay.portlet.display-category=category.sample",
        "com.liferay.portlet.instanceable=true",
        "javax.portlet.display-name=hello-you Portlet",
        "javax.portlet.init-param.template-path=/",
        "javax.portlet.init-param.view-template=/view.jsp",
        "javax.portlet.resource-bundle=content.Language",
        "javax.portlet.security-role-ref=power-user,user"
    },
    service = Portlet.class
)
public class HelloYouPortlet extends MVCPortlet {

    @Override
    public void render(RenderRequest renderRequest, 
                    RenderResponse renderResponse)
            throws IOException, PortletException
    {
        ThemeDisplay themeDisplay = (ThemeDisplay)
                    renderRequest.getAttribute(WebKeys.THEME\_DISPLAY);

        User user = themeDisplay.getUser();

        renderRequest.setAttribute("userName", 
                    user.getFirstName());



        super.render(renderRequest, renderResponse);
    }

}

Now we’re talking; here’s the real stuff. At the top is the @Component annotation, which tells the OSGi container how it should treat this module. By specifying immediate=true, you’re saying that when this module is deployed and all of its dependencies are satisfied, it should be started immediately instead of being lazy-loaded. Next are several properties specific to portlets: the category in which it should appear in Liferay’s UI, its display name, its default view, and more. Finally, the service–which is just a Java Interface–that it implements is defined, which is the portlet class.

Next, you have the class itself, which extends Liferay’s MVCPortlet class (that extends GenericPortlet, that implements Portlet). The only method overridden is the render() method, and Liferay’s API is used to get the user’s first name and put it in a request attribute called userName.

So you can see how this works: the portlet runs and retrieves the user’s first name, puts that in the request, and then by the use of the template path and view template properties specified in the @Component annotation, forwards processing to view.jsp, where the user’s first name is retrieved and displayed.

The only other item of interest is the bnd.bnd file:

Bundle-SymbolicName: com.liferay.docs.hello.you
Bundle-Version: 1.0.0

This declares the name of the module (sometimes also called a bundle). It’s a good practice to namespace it properly to avoid name conflicts in the container. The version is also declared, which allows the container to manage dependencies down to the version level of a module. This is called Semantic Versioning, and is a discussion by itself.

That’s all there is to this portlet. Next, you’ll see an extension, which in many cases is even simpler than a portlet.

Liferay’s UI is divided up into several areas. There’s the control menu and the product menu, which contains the add menu and the simulation menu. If you want to extend the UI, you can do that by deploying a module that adds what you want. In this example, you’ll add a link to the product menu, which is the menu that by default sits in the top right of the browser:

product-menu-unchanged.png

The product menu appears beneath the user’s profile link.

To this, you’ll add a link to this website:

product-menu-with-link.png

You can add links to the product menu by deploying a component.

As with the portlet project, this project’s layout contains only a few items that are easy to understand.

product-menu-project-layout.png

The product menu project is simpler than the portlet was.

As before, you have a build script, a bnd.bnd file that declares the module’s name and version, and this time, only a Java class and a language properties file.

The Java class defines only four methods:

@Component(
    immediate = true,
    property = {
        "product.navigation.control.menu.category.key=" +
                 ProductNavigationControlMenuCategoryKeys.USER,
        "product.navigation.control.menu.entry.order:Integer=1"
    },
    service = ProductNavigationControlMenuEntry.class
)
public class DevProductNavigationControlMenuEntry
    extends BaseProductNavigationControlMenuEntry
    implements ProductNavigationControlMenuEntry {

    @Override
    public String getIcon(HttpServletRequest request) {

        return "link";
    }

    @Override
    public String getLabel(Locale locale) {

        ResourceBundle resourceBundle = ResourceBundleUtil.getBundle(
            "content.Language", locale, getClass());

        return LanguageUtil.get(resourceBundle, "custom-message");
    }

    @Override
    public String getURL(HttpServletRequest request) {

        return "https://dev.liferay.com";

    }

    @Override
    public boolean isShow(HttpServletRequest request) throws 
        PortalException {

        return true;
    }

}

As before, this project was generated using a template from Blade CLI. The source code is part of the template; the only thing you’ll need to do is provide the link.

The first method gets the Font Awesome icon you want to use in the menu. The next gets the “label,” the text that appears when a user hovers the mouse over the link. This text is the value of the only property in the Language.properties file:

custom-message=Liferay Developer Network

The next method returns the URL that’s the destination for this link, and the final method returns a boolean for showing or hiding the link.

When you deploy this module, the link is added to the menu when the module starts. You don’t have to mess around looking in Liferay’s JSP or JavaScript files to customize the menu: it’s an extension point, and it is designed to be customized.

This is the modular paradigm for development. It helps you keep a clean separation of your code, whether it be applications or extensions, from the code that ships by default, and it gives you the power to customize the system dynamically, while it’s running, to avoid downtime. It is a different way of doing things, but we believe it’s a better way. When you start working with modules and see the benefits you can gain, we think you’ll agree.

How to Navigate Liferay’s Documentation

We’ve designed the Liferay Developer Network’s documentation pages to be easy to navigate, based on your role or the kind of information you’re looking for. If you have no idea where to start, the search box is front and center.

liferay-developer-network-home.png

The Liferay Developer Network is home to Liferay’s documentation.

Beyond that, though, the documentation is broken up into several categories:

  • User & Admin
  • Developer
  • Marketplace
  • Community

User & Admin focuses on documentation for two different but related groups: end users who want to use Liferay Portal and administrators who need information on setting Liferay Portal up and getting it running well. Accordingly, when you click on this section, you’re offered several options: User Guide (the default), Deployment, Reference, and Social Office, a product that used to be distributed with older versions of Liferay.

Developer contains the developer documentation, which includes both tutorials and something we call Learning Paths. Tutorials focus on topical content: if you’re in the middle of developing something and need to look up how a particular feature, framework, or API works, you’ll want a tutorial. Learning Paths are for when you want to start from the ground up and follow a series of lessons that take you on a tour through the most important things you need to know.

Marketplace shows developers how to get their apps on Liferay Marketplace, an app store for applications that run on Liferay Portal.

Community lists all the ways you can be involved in Liferay’s open source community. From helping QA, to fixing bugs, to contributing documentation or answering questions posted on the forum, you can be involved in almost every aspect of Liferay’s development.

Now you’re ready to explore some more about Liferay. We’re not planning to leave you here, as though this were a dead site. Please feel free to use the suggestions link at the bottom of every article you’ll encounter if you think something could be improved about that article. If you have feedback about the site itself, the feedback button is always floating at the bottom right. There are living, breathing people behind all the content on this site, and we stand ready to assist you on your Liferay journey.

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