|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.)
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.
Dec. 19, 2014 07:00 AM EST Reads: 2,129
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...
Dec. 19, 2014 06:30 AM EST Reads: 2,101
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...
Dec. 19, 2014 05:00 AM EST Reads: 1,925
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...
Dec. 19, 2014 04:00 AM EST Reads: 1,929
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.
Dec. 18, 2014 09:45 PM EST Reads: 924
“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.
Dec. 18, 2014 11:30 AM EST Reads: 966
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...
Dec. 18, 2014 10:30 AM EST Reads: 2,261
"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.
Dec. 18, 2014 10:00 AM EST Reads: 1,794
"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.
Dec. 18, 2014 09:00 AM EST Reads: 1,243
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...
Dec. 18, 2014 06:00 AM EST Reads: 776
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...
Dec. 17, 2014 11:15 PM EST Reads: 1,293
"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.
Dec. 17, 2014 11:00 PM EST Reads: 1,357
"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.
Dec. 17, 2014 08:00 PM EST Reads: 1,325
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...
Dec. 17, 2014 06:30 PM EST Reads: 1,236
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...
Dec. 17, 2014 11:45 AM EST Reads: 1,457
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...
Dec. 16, 2014 11:45 PM EST Reads: 1,298
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.
Dec. 15, 2014 11:45 PM EST Reads: 1,660
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.
Dec. 15, 2014 10:30 AM EST Reads: 6,871
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 ...
Dec. 15, 2014 10:00 AM EST Reads: 1,955
In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect at GE, and Ibrahim Gokcen, who leads GE's advanced IoT analytics, focused on the Internet of Things / Industrial Internet and how to make it operational for business end-users. Learn about the challenges posed by machine and sensor data and how to marry it with enterprise data. They also discussed the tips and tricks to provide the Industrial Internet as an end-user consumable service using Big Data Analytics and Industrial Cloud.
Dec. 15, 2014 10:00 AM EST Reads: 1,629