|By Tilak Mitra||
|April 5, 2004 12:00 AM EDT||
It has been well proven over the past few years that the best form of information exchange (in a typical B2B and B2C environment) is through XML. There are various XML-based standards (schema) for both the horizontal and vertical market sectors and there are ongoing efforts to move toward a standardized format in the various industry sectors.
With the proliferation of an XML-based information exchange, the industry is bound to write lots of Java code to consume XML Schema-based documents. Java Architecture for XML Binding (JAXB) provides a convenient way to bind an XML Schema to a representation in Java code, making it easy for developers to incorporate XML data and processing functions in applications based on Java technology without having to know much about the details of XML parsing.
How It Works
The use of JAXB starts from an XML Schema. Typically in an enterprise application, an XML Schema is defined that constitutes the business domain objects and their interrelationships.
The JAXB (binding) compiler creates a set of classes and interfaces from the XML Schema (see Figure 1). These sets of classes and interfaces are referenced and used in the application. The application developer has a rich set of JAXB APIs that he or she uses to convert a Java object tree/ structure (made up of the instances of classes generated by the binding compiler) to an XML document (that conforms to the XML Schema). The process of converting an XML document into a Java object tree is as seamless and easy as the former and the beauty of it all is that the developer does not have to write a single line of XML parsing routines in either of the conversion processes.
The process of converting a Java Object Tree to an XML document is known as marshalling, whereas the reverse process of converting an XML document to a Java Object Tree is called unmarshalling.
The process of creating the classes and interfaces from the XML Schema utilizes the JAXB binding compiler (xjc.bat or xjc.sh) that's included with the installation (see Resources section).
xjc.bat -p <package name> -d <working directory>
The -p option specifies the Java package for the generated classes and interfaces while the -d option specifies the working directory.
Once the classes and interfaces are generated, they can be used in the enterprise application. There are two typical usage scenarios.
1. Unmarshal an XML document to a Java object tree
JAXBContext jContext = JAXBContext.newInstance("<package name>") ;
where package name contains the JAXB generated classes.
Unmarshaller unmarshaller = jContext.createUnmarshaller() ;
Library library = (Library)unmarshaller.unmarshal(new
library.xml is an example XML document that conforms to the schema file from which the JAXB-generated Java classes and interfaces are created, and Library is the root object in the XML document.
Once a handle to the Library object instance is obtained, we're in the Java universe! The developer can use the power of Java to traverse through the object tree and use the same in the application, as required.
2. Marshal a Java object tree to an XML document
A JAXB implementation-provided class called ObjectFactory is used to create instances of the classes and interfaces that are generated by the JAXB binding compiler (during the generation process). This class uses the Factory pattern to create instances of the generated classes and this is the only way the class instances may be created.
Consider a small example in which a Library contains a list of Books in which each book has a title and a price field. The steps to create an XML document from the Java object tree are as follows:
ObjectFactory factory = new ObjectFactory() ;
Library library = factory.createLibrary() ;
Book bookOne = factory.createBook() ;
bookOne.setTitle("Design Patterns") ;
Book bookTwo = factory.createBook() ;
bookTwo.setTitle("Analysis Patterns") ;
Marshaller marshaller = jContext.createMarshaller() ;
marshaller.marshal(library, new FileOutputStream("library.xml")) ;
The power and flexibility of JAXB is further augmented by its customization feature that's added on top of the schema bindings. To add specific functionality to an application, JAXB binding customizations are used. These customizations are read and interpreted by the JAXB compiler. Customization is affected by annotating a schema with binding declarations that either override or extend the default bindings.
Customization has four scopes:
Although a detailed discussion about customization is beyond the scope of this article, it's worthwhile mentioning a few customization artifacts that are used more frequently in a typical JAXB usage scenario.
Customization bindings can be made at a global level of declaration that applies to all the defined elements in the XML Schema. Listing 1 provides a typical global customization binding.
Notice how in the listing defining the collectionType attribute tells the compiler that the type of collection used in the generated classes is of type ArrayList. The <xjc: serializable> element ensures that all the generated classes implement the Java Serializable marker interface. The <jxb: package> element's name attribute denotes the Java package in which the generated classes and interfaces are created.
All these elements' attributes can be tuned and configured to suit the requirements of the application.
Customization of the default binding can also be made at the element and its attribute's level. For example, an element can be adorned with its Javadoc by using annotations. Custom property names can also be specified that when defined, generate getter and setter methods for the property. This is illustrated in Listing 2. (Listing 2 can be downloaded from www.sys-con.com/java/sourcec.cfm.)
Notice how in the listing the <jxb: javadoc> element is used to create the documentation for the generated class. The <jxb:property> element is used to name an instance variable inside the generated class (Library class in this case) and generate its getter and setter methods. The generated class hence will have two methods: getBookList() and setBookList(...).
A detailed explanation of these bindings can be found in the Resources section (JAXB User's Guide).
Thinking in Terms of JAXB
In a typical enterprise application that's comprised of various application tiers, data is exchanged between these tiers to realize the business functionalities. It's a good design principle to create a data object model that can be used for inter-tier data exchange. This data object model is a good candidate to be represented in an XML Schema with JAXB customizations. With this design in place, data can be exchanged in either XML format or as Java objects while the JAXB libraries can be used to convert between XML and Java in a seamless fashion.
This article introduced the basic concepts of JAXB, how it works, and how it can be used in a Java-based enterprise application. It also provided a sneak peek at how JAXB customizations can be used to tailor an XML Schema to conform to the application requirements.
Part 2 will take a concrete example of an XML Schema and discuss the process of generating the classes and interfaces from a valid XML document and also the reverse process of creating an XML document from a Java object tree. Stay tuned!
(Note: The Reference Implementation of JAXB comes packaged inside the Java Web Services Developer's Pack [JWSDP]. Once this is installed, the JAXB compile time and runtime libraries are available in the <install-root>\jaxb directory.)
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...
Nov. 26, 2014 07:00 PM EST Reads: 1,266
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...
Nov. 26, 2014 07:00 PM EST Reads: 1,247
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 ...
Nov. 26, 2014 07:00 PM EST Reads: 966
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...
Nov. 26, 2014 06:45 PM EST Reads: 1,213
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...
Nov. 26, 2014 06:00 PM EST Reads: 1,318
"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.
Nov. 26, 2014 05:45 PM EST Reads: 1,235
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!
Nov. 26, 2014 04:00 PM EST Reads: 1,434
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.
Nov. 26, 2014 03:45 PM EST Reads: 1,400
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 ...
Nov. 26, 2014 02:00 PM EST Reads: 1,831
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.
Nov. 25, 2014 09:30 PM EST Reads: 1,845
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...
Nov. 25, 2014 09:30 PM EST Reads: 1,902
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...
Nov. 25, 2014 07:00 PM EST Reads: 1,789
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...
Nov. 25, 2014 04:30 PM EST Reads: 1,723
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...
Nov. 24, 2014 07:00 PM EST Reads: 2,081
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.
Nov. 24, 2014 12:00 PM EST Reads: 1,822
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 ...
Nov. 24, 2014 11:00 AM EST Reads: 2,183
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.
Nov. 24, 2014 09:00 AM EST Reads: 2,036
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.
Nov. 23, 2014 07:30 PM EST Reads: 2,195
"There is a natural synchronization between the business models, the IoT is there to support ,” explained Brendan O'Brien, Co-founder and Chief Architect of Aria Systems, in this SYS-CON.tv interview at the 15th International Cloud Expo®, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Nov. 23, 2014 12:00 PM EST Reads: 2,135
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...
Nov. 23, 2014 07:45 AM EST Reads: 2,213