Welcome!

Java Authors: Sematext Blog , Elizabeth White, Liz McMillan, Yeshim Deniz, Torben Andersen

Related Topics: Java

Java: Article

Seam: The Next Step in the Evolution of Web Applications

A powerful new application framework for managing contextual components

Web sites were originally static. Later dynamic content came about through CGI scripts paving the way for the first true Web applications. Since HTTP was entirely stateless, it became necessary to invent ways for requests to be linked together in a sequence. At first state was added to the URLs, but later the cookie concept came into being. By giving each user a special token, the server could maintain a context for each user, the HTTP session where the application can store state. As simple as it is, the HTTP session defines the entire concept of what a Web application is today.

The benefits of the HTTP session are clear, but we don't often stop to think about the drawbacks. When we use the HTTP session in a Web application, we store the sum total of the state of the user's interaction with the application in one place. This means that unless we jump through some seriously complex hoops, the user can only interact with an application in one way at a time.

Consider an application that manages a set of paged search results stored in the HTTP session. If the user were to start a new search in a new window, the new search would overwrite any previous session-scoped results. That's painful enough, but multitasking users aren't the only way session-scoped data causes Web applications to explode.

Consider our friend the back button, the mortal enemy of nearly every Web developer. When a user goes backwards in time to a previous page and presses a button, that application invocation expects to be associated with an HTTP session state that may have subsequently changed. When your application only has one context to store state, there's little hope of creating anything but the fragile Web applications that we all struggle with.

Most applications deal with this by adding state to the URLs, either going back to manually putting state information in the URLs or by adding a cookie-like token in the URL to point to a finer-grained context than the HTTP session. This can force the developer to pay a lot of attention to state management, often spending more time on it than on writing the actual application.

JBoss Seam
This article introduces JBoss Seam, a framework for managing contextual components. You'll see how Seam can manage state information in a Web application, overcoming the fundamental limitations of the HTTP session and enabling entirely new contexts that dramatically extend the capabilities of Web applications. It does all of this while simplifying your Web application development and reducing the amount of code (and XML) you have to write.

Seam is a framework for managing contextual components. What does that mean? Let's first look at a component. They go by many names: JavaBeans, POJOs, Enterprise JavaBeans. They're Java classes that provide some type of function to your application. A Java EE application might have many kinds of components: JSF backing beans creating the Web tier, entity beans providing persistence, and session beans providing business logic. To Seam, they're all components. Seam unifies these diverse component models, letting you think of them all as simply application components.

A Quick Example
The best way to see what Seam can do is to look at some examples. These examples are derived from the Seam DVD Store application. You can see the complete application in the examples directory of the Seam distribution. We'll start with a simple EJB3 entity bean for a product.

@Entity
@Name("product")
public class Product
    implements Serializable
{
     long id;
     String title;
     String description;
     float price;

     @Id @GeneratedValue(strategy=AUTO)
     public long getId() {
       return id;
     }
     public void setId(long id) {
       this.id = id;
     }

     public String getTitle() {
       return title;
     }
     public void setTitle(String title) {
       this.title = title;
     }

     // more getters and setters.
}

This is an EJB3 entity bean, a POJO with a couple of annotations. The only thing that stands out here is the @Name annotation, which marks it as a Seam component named product. We'll see later how this affects things. For now let's move on to an application component that displays a list of all the products in the system.

@Stateful
@Name("search")
@Interceptors(SeamInterceptor.class)
public class SearchAction
     implements Search
{
     @PersistenceContext(type=EXTENDED)
     private EntityManager em;

     @Out
     private List<Product> products;

     @Factory("products")
     public void loadProducts()
     {
       products = em.createQuery("from Product p")
       .getResultList();
     }
}

This is a stateful EJB3 session bean. We've marked it as a Seam component using the @Name annotation and brought in Seam functionality with the SeamInterceptor. Ignoring the remaining Seam annotations for a moment, what we have here is a simple component that keeps track of a list of Product objects.

The loadProducts() method uses the EJB3 persistence API to load that list of products. It makes use of EJB3 dependency injection to receive an EntityManager instance from the container so that it can load the the products into the product list.

The goal of this component is to provide this list of products to the UI. The @Out annotation on the product list does this. @Out marks the list as data to be shared out to the UI.

Let's jump forward to the view. This is part of the Facelets XHTML template, but for our purposes you can think of it as a JSP file that uses the JavaServer Faces tag libraries. The dataTable tag renders the list of items in table form using the three column definitions: title, description, and price.

<h:dataTable value="#{products}" var="prod">
   <h:column>
     <f:facet name="header">title</f:facet>
     #{prod.title}
   </h:column>
   <h:column>
     <f:facet name="header">description</f:facet>
     #{prod.description}
   </h:column>
   <h:column>
     <f:facet name="header">price</f:facet>
     #{prod.price}
   </h:column>
</h:dataTable>

The search component provides the products value for the table to the view, but how does the value get populated in the view? The @Factory annotation on the loadProducts() method tells Seam that if a view needs a products value, the loadProducts() method can be used as a factory method to load the products from the database.

There's something else happening here. SearchAction is a stateful session bean, and the product's value is just part of its state. Stateful components have a lifecycle. They have to be created, kept around, and eventually destroyed. In Seam, stateful components have the lifecycle of their surrounding context. If a stateful component were session-scoped, for example, it would be stored in the HTTP session and destroyed when the HTTP session is destroyed, unless it reaches its natural end of life sooner.

We mentioned earlier that Seam has several more interesting contexts than just simple session-scoped data. Stateful components, by default, have conversational scope. A conversation is a sequence of clicks within a Web application. You can think of it as an actual conversation with part of the application. You interact with one part of the application for a few clicks and say good-bye, maybe moving on to some other part of the application.

More Stories By Norman Richards

Norman Richards is a JBoss developer living in Austin, Tx. He is co-author of JBoss: A Developer's Notebook and XDoclet in Action.

Comments (1) View Comments

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


Most Recent Comments
SYS-CON Belgium News Desk 02/19/06 01:41:18 PM EST

Web sites were originally static. Later dynamic content came about through CGI scripts paving the way for the first true Web applications. Since HTTP was entirely stateless, it became necessary to invent ways for requests to be linked together in a sequence. At first state was added to the URLs, but later the cookie concept came into being. By giving each user a special token, the server could maintain a context for each user, the HTTP session where the application can store state. As simple as it is, the HTTP session defines the entire concept of what a Web application is today.

@ThingsExpo Stories
The BPM world is going through some evolution or changes where traditional business process management solutions really have nowhere to go in terms of development of the road map. In this demo at 15th Cloud Expo, Kyle Hansen, Director of Professional Services at AgilePoint, shows AgilePoint’s unique approach to dealing with this market circumstance by developing a rapid application composition or development framework.

ARMONK, N.Y., Nov. 20, 2014 /PRNewswire/ --  IBM (NYSE: IBM) today announced that it is bringing a greater level of control, security and flexibility to cloud-based application development and delivery with a single-tenant version of Bluemix, IBM's platform-as-a-service. The new platform enables developers to build ap...

"BSQUARE is in the business of selling software solutions for smart connected devices. It's obvious that IoT has moved from being a technology to being a fundamental part of business, and in the last 18 months people have said let's figure out how to do it and let's put some focus on it, " explained Dave Wagstaff, VP & Chief Architect, at BSQUARE Corporation, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
The major cloud platforms defy a simple, side-by-side analysis. Each of the major IaaS public-cloud platforms offers their own unique strengths and functionality. Options for on-site private cloud are diverse as well, and must be designed and deployed while taking existing legacy architecture and infrastructure into account. Then the reality is that most enterprises are embarking on a hybrid cloud strategy and programs. In this Power Panel at 15th Cloud Expo (http://www.CloudComputingExpo.com), moderated by Ashar Baig, Research Director, Cloud, at Gigaom Research, Nate Gordon, Director of T...
The Internet of Things is not new. Historically, smart businesses have used its basic concept of leveraging data to drive better decision making and have capitalized on those insights to realize additional revenue opportunities. So, what has changed to make the Internet of Things one of the hottest topics in tech? In his session at @ThingsExpo, Chris Gray, Director, Embedded and Internet of Things, discussed the underlying factors that are driving the economics of intelligent systems. Discover how hardware commoditization, the ubiquitous nature of connectivity, and the emergence of Big Data a...
SYS-CON Events announced today that Windstream, a leading provider of advanced network and cloud communications, has been named “Silver Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9–11, 2015, at the Javits Center in New York, NY. Windstream (Nasdaq: WIN), a FORTUNE 500 and S&P 500 company, is a leading provider of advanced network communications, including cloud computing and managed services, to businesses nationwide. The company also offers broadband, phone and digital TV services to consumers primarily in rural areas.
“In the past year we've seen a lot of stabilization of WebRTC. You can now use it in production with a far greater degree of certainty. A lot of the real developments in the past year have been in things like the data channel, which will enable a whole new type of application," explained Peter Dunkley, Technical Director at Acision, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that IDenticard will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. IDenticard™ is the security division of Brady Corp (NYSE: BRC), a $1.5 billion manufacturer of identification products. We have small-company values with the strength and stability of a major corporation. IDenticard offers local sales, support and service to our customers across the United States and Canada. Our partner network encompasses some 300 of the world's leading systems integrators and security s...
DevOps Summit 2015 New York, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that it is now accepting Keynote Proposals. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long development cycles that produce software that is obsolete at launch. DevOps may be disruptive, but it is essential.
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Nigeria has the largest economy in Africa, at more than US$500 billion, and ranks 23rd in the world. A recent re-evaluation of Nigeria's true economic size doubled the previous estimate, and brought it well ahead of South Africa, which is a member (unlike Nigeria) of the G20 club for political as well as economic reasons. Nigeria's economy can be said to be quite diverse from one point of view, but heavily dependent on oil and gas at the same time. Oil and natural gas account for about 15% of Nigera's overall economy, but traditionally represent more than 90% of the country's exports and as...
The Internet of Things is a misnomer. That implies that everything is on the Internet, and that simply should not be - especially for things that are blurring the line between medical devices that stimulate like a pacemaker and quantified self-sensors like a pedometer or pulse tracker. The mesh of things that we manage must be segmented into zones of trust for sensing data, transmitting data, receiving command and control administrative changes, and peer-to-peer mesh messaging. In his session at @ThingsExpo, Ryan Bagnulo, Solution Architect / Software Engineer at SOA Software, focused on desi...
"At our booth we are showing how to provide trust in the Internet of Things. Trust is where everything starts to become secure and trustworthy. Now with the scaling of the Internet of Things it becomes an interesting question – I've heard numbers from 200 billion devices next year up to a trillion in the next 10 to 15 years," explained Johannes Lintzen, Vice President of Sales at Utimaco, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
"For over 25 years we have been working with a lot of enterprise customers and we have seen how companies create applications. And now that we have moved to cloud computing, mobile, social and the Internet of Things, we see that the market needs a new way of creating applications," stated Jesse Shiah, CEO, President and Co-Founder of AgilePoint Inc., in this SYS-CON.tv interview at 15th Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that Gridstore™, the leader in hyper-converged infrastructure purpose-built to optimize Microsoft workloads, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Gridstore™ is the leader in hyper-converged infrastructure purpose-built for Microsoft workloads and designed to accelerate applications in virtualized environments. Gridstore’s hyper-converged infrastructure is the industry’s first all flash version of HyperConverged Appliances that include both compute and storag...
Today’s enterprise is being driven by disruptive competitive and human capital requirements to provide enterprise application access through not only desktops, but also mobile devices. To retrofit existing programs across all these devices using traditional programming methods is very costly and time consuming – often prohibitively so. In his session at @ThingsExpo, Jesse Shiah, CEO, President, and Co-Founder of AgilePoint Inc., discussed how you can create applications that run on all mobile devices as well as laptops and desktops using a visual drag-and-drop application – and eForms-buildi...
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
Code Halos - aka "digital fingerprints" - are the key organizing principle to understand a) how dumb things become smart and b) how to monetize this dynamic. In his session at @ThingsExpo, Robert Brown, AVP, Center for the Future of Work at Cognizant Technology Solutions, outlined research, analysis and recommendations from his recently published book on this phenomena on the way leading edge organizations like GE and Disney are unlocking the Internet of Things opportunity and what steps your organization should be taking to position itself for the next platform of digital competition.
The 3rd International Internet of @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that its Call for Papers is now open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
As the Internet of Things unfolds, mobile and wearable devices are blurring the line between physical and digital, integrating ever more closely with our interests, our routines, our daily lives. Contextual computing and smart, sensor-equipped spaces bring the potential to walk through a world that recognizes us and responds accordingly. We become continuous transmitters and receivers of data. In his session at @ThingsExpo, Andrew Bolwell, Director of Innovation for HP's Printing and Personal Systems Group, discussed how key attributes of mobile technology – touch input, sensors, social, and ...