Welcome!

Java IoT Authors: Pat Romanski, Yeshim Deniz, Zakia Bouachraoui, Elizabeth White, Liz McMillan

Related Topics: Java IoT

Java IoT: Article

Writing Classpath-less J2EE Clients...

...using a simple technique

The thin J2EE client approach is faster than Web services, since it uses native communication protocols while making remote calls over the network. However, it's better suited for clients operating in intranet environments where there is a greater degree of control over the client's deployment and the J2EE server. A downside for this environment is passing through firewalls. Furthermore, this approach provides clients with secure access to the application business logic while at the same time taking care of the details of the client and server communication and marshalling and unmarshalling parameters.

Java Message Service (JMS) is another means for thin J2EE clients to communicate with server applications. It provides a means for asynchronous communication. Applications using JMS are better suited to a setting that is behind a firewall, since messaging systems generally don't work well on the Internet (often, messaging systems are not even exposed on the Internet).

Using Thin Clients with the WebLogic Server
Check your J2EE application server documentation to see if it comes with a resource to serve objects to the client. For example, the WebLogic server contains a built-in servlet, called ClasspathServlet, to serve Java resources in a distributed manner. The servlet code in Listing 2 is not required, since this feature comes out-of-the-box in WebLogic. The URL syntax is as follows:

http://<servername>:<port>/bea_wls_internal/classes

The bea_wls_internal is a default Web application that is enabled by default. The /classes part of the URL is registered to the internal weblogic.servlet.ClasspathServlet.

If the URL is set to /bea_wls_internal/classes, the classes required by the thin J2EE client should be available in the system classpath of the server.

If the URL is set to /bea_wls_internal/classes/[email protected], the classes required by the thin J2EE client should be in the applications/DefaultWebApp/WEB-INF/classes directory or in the system classpath.

Versions prior to WebLogic 7 must register the ClasspathServlet and it's accessed via the /classes URL.

For this to operate successfully, you must add the following parameter to the WebLogic start script:

-Dweblogic.servlet.ClasspathServlet.disableStrictCheck=true

This relaxes the restriction of the downloadable file type. Hence, any Java resource can be served from this servlet.

Java Web Start
Java Web Start (JSR 000056) is a built-in J2SE software-distribution mechanism that downloads and executes Java software from a HTTP server. Typically, it's used from a browser and works well with the Java plug-in. The Java Network Language Protocol (JNLP) is the underlying communication mechanism used by Java Web Start. Alternatively, Java Web Start can be invoked from the command line using the javaws utility.

The techniques presented in this article are not meant as a replacement for Java Web Start. They simply demonstrate how to create lightweight clients in your own programs when you need to selectively download and execute application code.

Summary
As service-oriented architectures reemerge, it becomes crucial to have a decoupled and extensible client layer that can accommodate change and dynamic behavior. Constant API changes and backward compatibility problems can occur during concurrent development cycles. For an architecture that consists of all Java components (both client and server), Web services may not be the best choice, since it can cause performance degradation (overhead of XML parsing), deployment problems (load balancing/failover), and security issues.

Utilizing the native application server features, such as clustering, transactions, and security, with a loosely coupled implementation, architectures can focus on integration versus environmental problems. Constant API changes and backward compatibility problems can occur during concurrent development cycles. Building a very thin client layer can facilitate dynamic code changes and provide an adaptable and extensible architecture.

Resources

  • Tutorial: Getting Started Using RMI-IIOP: http://java.sun.com/j2se/1.4.2/docs/guide/rmi-iiop/tutorial.html
  • Java Web Start FAQ: Click Here
  • java.net: Class URLClassLoader: http://java.sun.com/j2se/1.4.2/docs/api/java/net/URLClassLoader.html
  • More Stories By Bahar Limaye

    Bahar Limaye is a system architect at The College Board. He has extensive experience building distributed object-oriented systems.

    Comments (3) 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
    Venkat 01/09/08 04:19:06 PM EST

    Thank you very much for such a great Article. It solved my problem.

    PL 03/07/05 08:38:46 PM EST

    Wow. this article solved almost exactly the problem i was running into. it really works!

    Marat 02/18/05 07:29:37 PM EST

    You might want to take a look at our site as most of the J2EE APIs (JMS, EJB, RMI, CORBA and JAX-RPC) are available with a runtime of fixed size ~150 KB, App Server independent. No App Server resources are ever loaded onto the client but yet all of those API are accessible over the HTTP protocol (the Internet)

    See a full blown JMS client in action over HTTP here:

    http://www.jproxy.com/thinlet/demo.html

    Cheers,
    Marat

    IoT & Smart Cities Stories
    CloudEXPO | DevOpsSUMMIT | DXWorldEXPO are the world's most influential, independent events where Cloud Computing was coined and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals. Sponsors of DXWorldEXPO | CloudEXPO benefit from unmatched branding, profile building and lead generation opportunities.
    All in Mobile is a place where we continually maximize their impact by fostering understanding, empathy, insights, creativity and joy. They believe that a truly useful and desirable mobile app doesn't need the brightest idea or the most advanced technology. A great product begins with understanding people. It's easy to think that customers will love your app, but can you justify it? They make sure your final app is something that users truly want and need. The only way to do this is by ...
    Digital Transformation and Disruption, Amazon Style - What You Can Learn. Chris Kocher is a co-founder of Grey Heron, a management and strategic marketing consulting firm. He has 25+ years in both strategic and hands-on operating experience helping executives and investors build revenues and shareholder value. He has consulted with over 130 companies on innovating with new business models, product strategies and monetization. Chris has held management positions at HP and Symantec in addition to ...
    Dynatrace is an application performance management software company with products for the information technology departments and digital business owners of medium and large businesses. Building the Future of Monitoring with Artificial Intelligence. 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 busine...
    The challenges of aggregating data from consumer-oriented devices, such as wearable technologies and smart thermostats, are fairly well-understood. However, there are a new set of challenges for IoT devices that generate megabytes or gigabytes of data per second. Certainly, the infrastructure will have to change, as those volumes of data will likely overwhelm the available bandwidth for aggregating the data into a central repository. Ochandarena discusses a whole new way to think about your next...
    DXWorldEXPO LLC announced today that Big Data Federation to Exhibit at the 22nd International CloudEXPO, colocated with DevOpsSUMMIT and DXWorldEXPO, November 12-13, 2018 in New York City. Big Data Federation, Inc. develops and applies artificial intelligence to predict financial and economic events that matter. The company uncovers patterns and precise drivers of performance and outcomes with the aid of machine-learning algorithms, big data, and fundamental analysis. Their products are deployed...
    Cell networks have the advantage of long-range communications, reaching an estimated 90% of the world. But cell networks such as 2G, 3G and LTE consume lots of power and were designed for connecting people. They are not optimized for low- or battery-powered devices or for IoT applications with infrequently transmitted data. Cell IoT modules that support narrow-band IoT and 4G cell networks will enable cell connectivity, device management, and app enablement for low-power wide-area network IoT. B...
    The hierarchical architecture that distributes "compute" within the network specially at the edge can enable new services by harnessing emerging technologies. But Edge-Compute comes at increased cost that needs to be managed and potentially augmented by creative architecture solutions as there will always a catching-up with the capacity demands. Processing power in smartphones has enhanced YoY and there is increasingly spare compute capacity that can be potentially pooled. Uber has successfully ...
    SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
    When talking IoT we often focus on the devices, the sensors, the hardware itself. The new smart appliances, the new smart or self-driving cars (which are amalgamations of many ‘things'). When we are looking at the world of IoT, we should take a step back, look at the big picture. What value are these devices providing. IoT is not about the devices, its about the data consumed and generated. The devices are tools, mechanisms, conduits. This paper discusses the considerations when dealing with the...