Welcome!

Java IoT Authors: Liz McMillan, Pat Romanski, Carmen Gonzalez, Yeshim Deniz, Antonella Corno

Related Topics: Java IoT

Java IoT: Article

Client/Server Is Not the Only Fruit

Client/Server Is Not the Only Fruit

The vast majority of Java enterprise applications are architected along the lines of Sun's original PetStore showcase application. Rather than seeing this as a market stall displaying all the J2EE goods on offer, developers took it as a blueprint for enterprise applications. It certainly created a lot of work for Java application developers (as well as systems administrators and systems integrators), but whether most of the applications needed most of the possible layers - including bean-managed persistence and the ubiquitous DAO - is open for question at the very least. This article briefly describes some of the testability shortcomings of the traditional J2EE model and presents some alternatives.

The J2EE Model
With J2EE we are tied to a single logical server in a client/server architecture, and any component such as a servlet or EJB has to be deployed to the server (potentially a time-consuming process) before we know whether it works. This makes it difficult to use test-driven techniques to develop these components. To make a small change to such a component requires a code change, a recompile, and a redeploy. On many commercial application servers this sequence of events takes too long to be repeated as frequently as TDD requires. The developer is encouraged to deploy bigger changes less often, and therefore has a higher risk of introducing errors.

A few patterns alleviate some of this, most notably the Front Controller/Dispatcher pattern. This has a single component (a servlet in the Web container or a stateless session bean in the EJB tier) that dispatches requests to a POJO (Plain Old Java Object). A POJO is much better suited for unit testing - we can simply instantiate it in a known state and then exercise its behavior. From a TDD perspective, this is what makes a framework like WebWork more "agile" than Struts; for instance, the actual components are testable outside of a container.

Service-Oriented Architectures
J2EE encourages us to model a system in terms of components interacting with one another. Instead we can model in terms of services that an application provides or "things that it does." These services can exist on different machines or in different virtual machines on the same host. As long as we have a means of locating a service, we can use it. In terms of testability, this makes life a lot easier for us. A service is simply a class that implements an interface, so we can test its behavior in isolation or in conjunction with other services just by instantiating a service object and calling methods on it.

Service-oriented mechanisms such as SOAP, XML-RPC, or JINI are cleanly separated from the actual services they advertise. Compare this to a session bean, which is tightly coupled to its container: it requires a number of container-specific classes just to function (such as a javax.ejb. SessionContext), and has a whole complex life cycle associated with it. Both of these make testing a session bean a lot more complex - and add greatly to the time it takes to make a change and test it.

Event-Driven Architectures
So far we have focused on synchronous behavior. The concept of modeling a system in terms of messages or events being produced and consumed asynchronously from queues is very powerful and yet still largely overlooked. Event-driven systems are renowned for their resilience, but they also lend themselves very nicely to a test-driven approach. As with services, an event consumer or listener is typically a Java class that implements an interface. As long as the consumer class is decoupled from the delivery mechanism, we can easily test its behavior. We can model synchronous behavior asynchronously to gain both scalability and testability. A Staged, Event-Driven Architecture (SEDA) simulates synchronous processing by means of a series of stages, each represented by a queue. Thus each stage can be unit-tested and developed separately.

Summary
When you're writing an enterprise application in Java, you shouldn't feel constrained to the classic J2EE model. Investigate some of the alternatives; ask lots of questions; and evaluate the costs, benefits, and risks of using a different approach. But most important, as a developer try to find an architecture that enables you to write testable code. Remember, PetStore is a showcase of technologies, not a blueprint.

More Stories By Dan North

Dan North has been writing software for 12 years, and is a programmer and coach for ThoughtWorks (www.thoughtworks.com), a software development consultancy, where he encourages people to write tests.

Comments (2) 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
Tom 03/10/04 12:44:18 AM EST

I agree on the statements made here. Personally I use the approach of moving all logic into POJO''s, which have no knowledge of how their functionality is made public. The servlet or EJB or webservice doing that, is just a hand-through taking care of the appropriate protocol.

Tom 03/10/04 12:43:24 AM EST

I agree on the statements made here. Personally I use the approach of moving all logic into POJO''s, which have no knowledge of how their functionality is made public. The servlet or EJB or webserver doing that, is just a hand-through taking care data of the appropriate protocol.

@ThingsExpo Stories
SYS-CON Events announced today that CollabNet, a global leader in enterprise software development, release automation and DevOps solutions, will be a Bronze Sponsor of SYS-CON's 20th International Cloud Expo®, taking place from June 6-8, 2017, at the Javits Center in New York City, NY. CollabNet offers a broad range of solutions with the mission of helping modern organizations deliver quality software at speed. The company’s latest innovation, the DevOps Lifecycle Manager (DLM), supports Value S...
SYS-CON Events announced today that Juniper Networks (NYSE: JNPR), an industry leader in automated, scalable and secure networks, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Juniper Networks challenges the status quo with products, solutions and services that transform the economics of networking. The company co-innovates with customers and partners to deliver automated, scalable and secure network...
Bert Loomis was a visionary. This general session will highlight how Bert Loomis and people like him inspire us to build great things with small inventions. In their general session at 19th Cloud Expo, Harold Hannon, Architect at IBM Bluemix, and Michael O'Neill, Strategic Business Development at Nvidia, discussed the accelerating pace of AI development and how IBM Cloud and NVIDIA are partnering to bring AI capabilities to "every day," on-demand. They also reviewed two "free infrastructure" pr...
Five years ago development was seen as a dead-end career, now it’s anything but – with an explosion in mobile and IoT initiatives increasing the demand for skilled engineers. But apart from having a ready supply of great coders, what constitutes true ‘DevOps Royalty’? It’ll be the ability to craft resilient architectures, supportability, security everywhere across the software lifecycle. In his keynote at @DevOpsSummit at 20th Cloud Expo, Jeffrey Scheaffer, GM and SVP, Continuous Delivery Busine...
SYS-CON Events announced today that Hitachi, the leading provider the Internet of Things and Digital Transformation, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Hitachi Data Systems, a wholly owned subsidiary of Hitachi, Ltd., offers an integrated portfolio of services and solutions that enable digital transformation through enhanced data management, governance, mobility and analytics. We help globa...
SYS-CON Events announced today that T-Mobile will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. As America's Un-carrier, T-Mobile US, Inc., is redefining the way consumers and businesses buy wireless services through leading product and service innovation. The Company's advanced nationwide 4G LTE network delivers outstanding wireless experiences to 67.4 million customers who are unwilling to compromise on ...
SYS-CON Events announced today that Super Micro Computer, Inc., a global leader in compute, storage and networking technologies, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Supermicro (NASDAQ: SMCI), the leading innovator in high-performance, high-efficiency server technology, is a premier provider of advanced server Building Block Solutions® for Data Center, Cloud Computing, Enterprise IT, Hadoop/...
With billions of sensors deployed worldwide, the amount of machine-generated data will soon exceed what our networks can handle. But consumers and businesses will expect seamless experiences and real-time responsiveness. What does this mean for IoT devices and the infrastructure that supports them? More of the data will need to be handled at - or closer to - the devices themselves.
SYS-CON Events announced today that DatacenterDynamics has been named “Media Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY. DatacenterDynamics is a brand of DCD Group, a global B2B media and publishing company that develops products to help senior professionals in the world's most ICT dependent organizations make risk-based infrastructure and capacity decisions.
NHK, Japan Broadcasting, will feature the upcoming @ThingsExpo Silicon Valley in a special 'Internet of Things' and smart technology documentary that will be filmed on the expo floor between November 3 to 5, 2015, in Santa Clara. NHK is the sole public TV network in Japan equivalent to the BBC in the UK and the largest in Asia with many award-winning science and technology programs. Japanese TV is producing a documentary about IoT and Smart technology and will be covering @ThingsExpo Silicon Val...
The explosion of new web/cloud/IoT-based applications and the data they generate are transforming our world right before our eyes. In this rush to adopt these new technologies, organizations are often ignoring fundamental questions concerning who owns the data and failing to ask for permission to conduct invasive surveillance of their customers. Organizations that are not transparent about how their systems gather data telemetry without offering shared data ownership risk product rejection, regu...
The 20th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held June 6-8, 2017, at the Javits Center in New York City, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Containers, Microservices and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportunity. Submit your speaking proposal ...
Grape Up is a software company, specialized in cloud native application development and professional services related to Cloud Foundry PaaS. With five expert teams that operate in various sectors of the market across the USA and Europe, we work with a variety of customers from emerging startups to Fortune 1000 companies.
Financial Technology has become a topic of intense interest throughout the cloud developer and enterprise IT communities. Accordingly, attendees at the upcoming 20th Cloud Expo at the Javits Center in New York, June 6-8, 2017, will find fresh new content in a new track called FinTech.
@GonzalezCarmen has been ranked the Number One Influencer and @ThingsExpo has been named the Number One Brand in the “M2M 2016: Top 100 Influencers and Brands” by Analytic. Onalytica analyzed tweets over the last 6 months mentioning the keywords M2M OR “Machine to Machine.” They then identified the top 100 most influential brands and individuals leading the discussion on Twitter.
In his keynote at @ThingsExpo, Chris Matthieu, Director of IoT Engineering at Citrix and co-founder and CTO of Octoblu, focused on building an IoT platform and company. He provided a behind-the-scenes look at Octoblu’s platform, business, and pivots along the way (including the Citrix acquisition of Octoblu).
Cognitive Computing is becoming the foundation for a new generation of solutions that have the potential to transform business. Unlike traditional approaches to building solutions, a cognitive computing approach allows the data to help determine the way applications are designed. This contrasts with conventional software development that begins with defining logic based on the current way a business operates. In her session at 18th Cloud Expo, Judith S. Hurwitz, President and CEO of Hurwitz & ...
SYS-CON Events announced today that Interoute, owner-operator of one of Europe's largest networks and a global cloud services platform, has been named “Bronze Sponsor” of SYS-CON's 20th Cloud Expo, which will take place on June 6-8, 2017 at the Javits Center in New York, New York. Interoute is the owner-operator of one of Europe's largest networks and a global cloud services platform which encompasses 12 data centers, 14 virtual data centers and 31 colocation centers, with connections to 195 add...
Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more business becomes digital the more stakeholders are interested in this data including how it relates to business. Some of these people have never used a monitoring tool before. They have a question on their mind like “How is my application doing” but no id...
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo 2016 in New York. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place June 6-8, 2017, at the Javits Center in New York City, New York, is co-located with 20th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry p...