Welcome!

Java Authors: Pat Romanski, Carmen Gonzalez, Victoria Livschitz, Liz McMillan, Elizabeth White

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
Cultural, regulatory, environmental, political and economic (CREPE) conditions over the past decade are creating cross-industry solution spaces that require processes and technologies from both the Internet of Things (IoT), and Data Management and Analytics (DMA). These solution spaces are evolving into Sensor Analytics Ecosystems (SAE) that represent significant new opportunities for organizations of all types. Public Utilities throughout the world, providing electricity, natural gas and water, are pursuing SmartGrid initiatives that represent one of the more mature examples of SAE. We have s...
The security devil is always in the details of the attack: the ones you've endured, the ones you prepare yourself to fend off, and the ones that, you fear, will catch you completely unaware and defenseless. The Internet of Things (IoT) is nothing if not an endless proliferation of details. It's the vision of a world in which continuous Internet connectivity and addressability is embedded into a growing range of human artifacts, into the natural world, and even into our smartphones, appliances, and physical persons. In the IoT vision, every new "thing" - sensor, actuator, data source, data con...
How do APIs and IoT relate? The answer is not as simple as merely adding an API on top of a dumb device, but rather about understanding the architectural patterns for implementing an IoT fabric. There are typically two or three trends: Exposing the device to a management framework Exposing that management framework to a business centric logic Exposing that business layer and data to end users. This last trend is the IoT stack, which involves a new shift in the separation of what stuff happens, where data lives and where the interface lies. For instance, it's a mix of architectural styles ...
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.
The Internet of Things is tied together with a thin strand that is known as time. Coincidentally, at the core of nearly all data analytics is a timestamp. When working with time series data there are a few core principles that everyone should consider, especially across datasets where time is the common boundary. In his session at Internet of @ThingsExpo, Jim Scott, Director of Enterprise Strategy & Architecture at MapR Technologies, discussed single-value, geo-spatial, and log time series data. By focusing on enterprise applications and the data center, he will use OpenTSDB as an example t...
An entirely new security model is needed for the Internet of Things, or is it? Can we save some old and tested controls for this new and different environment? In his session at @ThingsExpo, New York's at the Javits Center, Davi Ottenheimer, EMC Senior Director of Trust, reviewed hands-on lessons with IoT devices and reveal a new risk balance you might not expect. Davi Ottenheimer, EMC Senior Director of Trust, has more than nineteen years' experience managing global security operations and assessments, including a decade of leading incident response and digital forensics. He is co-author of t...
The Internet of Things will greatly expand the opportunities for data collection and new business models driven off of that data. In her session at @ThingsExpo, Esmeralda Swartz, CMO of MetraTech, discussed how for this to be effective you not only need to have infrastructure and operational models capable of utilizing this new phenomenon, but increasingly service providers will need to convince a skeptical public to participate. Get ready to show them the money!
The Internet of Things will put IT to its ultimate test by creating infinite new opportunities to digitize products and services, generate and analyze new data to improve customer satisfaction, and discover new ways to gain a competitive advantage across nearly every industry. In order to help corporate business units to capitalize on the rapidly evolving IoT opportunities, IT must stand up to a new set of challenges. In his session at @ThingsExpo, Jeff Kaplan, Managing Director of THINKstrategies, will examine why IT must finally fulfill its role in support of its SBUs or face a new round of...
One of the biggest challenges when developing connected devices is identifying user value and delivering it through successful user experiences. In his session at Internet of @ThingsExpo, Mike Kuniavsky, Principal Scientist, Innovation Services at PARC, described an IoT-specific approach to user experience design that combines approaches from interaction design, industrial design and service design to create experiences that go beyond simple connected gadgets to create lasting, multi-device experiences grounded in people's real needs and desires.
Enthusiasm for the Internet of Things has reached an all-time high. In 2013 alone, venture capitalists spent more than $1 billion dollars investing in the IoT space. With "smart" appliances and devices, IoT covers wearable smart devices, cloud services to hardware companies. Nest, a Google company, detects temperatures inside homes and automatically adjusts it by tracking its user's habit. These technologies are quickly developing and with it come challenges such as bridging infrastructure gaps, abiding by privacy concerns and making the concept a reality. These challenges can't be addressed w...
The Domain Name Service (DNS) is one of the most important components in networking infrastructure, enabling users and services to access applications by translating URLs (names) into IP addresses (numbers). Because every icon and URL and all embedded content on a website requires a DNS lookup loading complex sites necessitates hundreds of DNS queries. In addition, as more internet-enabled ‘Things' get connected, people will rely on DNS to name and find their fridges, toasters and toilets. According to a recent IDG Research Services Survey this rate of traffic will only grow. What's driving t...
Connected devices and the Internet of Things are getting significant momentum in 2014. In his session at Internet of @ThingsExpo, Jim Hunter, Chief Scientist & Technology Evangelist at Greenwave Systems, examined three key elements that together will drive mass adoption of the IoT before the end of 2015. The first element is the recent advent of robust open source protocols (like AllJoyn and WebRTC) that facilitate M2M communication. The second is broad availability of flexible, cost-effective storage designed to handle the massive surge in back-end data in a world where timely analytics is e...
Scott Jenson leads a project called The Physical Web within the Chrome team at Google. Project members are working to take the scalability and openness of the web and use it to talk to the exponentially exploding range of smart devices. Nearly every company today working on the IoT comes up with the same basic solution: use my server and you'll be fine. But if we really believe there will be trillions of these devices, that just can't scale. We need a system that is open a scalable and by using the URL as a basic building block, we open this up and get the same resilience that the web enjoys.
"Matrix is an ambitious open standard and implementation that's set up to break down the fragmentation problems that exist in IP messaging and VoIP communication," explained John Woolf, Technical Evangelist at Matrix, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
We are reaching the end of the beginning with WebRTC, and real systems using this technology have begun to appear. One challenge that faces every WebRTC deployment (in some form or another) is identity management. For example, if you have an existing service – possibly built on a variety of different PaaS/SaaS offerings – and you want to add real-time communications you are faced with a challenge relating to user management, authentication, authorization, and validation. Service providers will want to use their existing identities, but these will have credentials already that are (hopefully) i...
P2P RTC will impact the landscape of communications, shifting from traditional telephony style communications models to OTT (Over-The-Top) cloud assisted & PaaS (Platform as a Service) communication services. The P2P shift will impact many areas of our lives, from mobile communication, human interactive web services, RTC and telephony infrastructure, user federation, security and privacy implications, business costs, and scalability. In his session at @ThingsExpo, Robin Raymond, Chief Architect at Hookflash, will walk through the shifting landscape of traditional telephone and voice services ...
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at Internet of @ThingsExpo, James Kirkland, Chief Architect for the Internet of Things and Intelligent Systems at Red Hat, described how to revolutioniz...
Bit6 today issued a challenge to the technology community implementing Web Real Time Communication (WebRTC). To leap beyond WebRTC’s significant limitations and fully leverage its underlying value to accelerate innovation, application developers need to consider the entire communications ecosystem.
The definition of IoT is not new, in fact it’s been around for over a decade. What has changed is the public's awareness that the technology we use on a daily basis has caught up on the vision of an always on, always connected world. If you look into the details of what comprises the IoT, you’ll see that it includes everything from cloud computing, Big Data analytics, “Things,” Web communication, applications, network, storage, etc. It is essentially including everything connected online from hardware to software, or as we like to say, it’s an Internet of many different things. The difference ...
Cloud Expo 2014 TV commercials will feature @ThingsExpo, which was launched in June, 2014 at New York City's Javits Center as the largest 'Internet of Things' event in the world.