Welcome!

Java IoT Authors: Automic Blog, Liz McMillan, Elizabeth White, Pat Romanski, Roger Strukhoff

Related Topics: Java IoT

Java IoT: Article

Using JAXB in Enterprise J2EE Applications

Incorporate XML data and processing functions Part 1

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

  • To achieve this, an instance of a JAXBContext object needs to be created:

    JAXBContext jContext = JAXBContext.newInstance("<package name>") ;

    where package name contains the JAXB generated classes.

  • An unmarshaller instance is created:

    Unmarshaller unmarshaller = jContext.createUnmarshaller() ;

  • The XML document is read in and a handle to the root Java object in the XML document is obtained:

    Library library = (Library)unmarshaller.unmarshal(new
    FileInputStream("library.xml") ;

    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:

  • Obtain an instance of ObjectFactory:

    ObjectFactory factory = new ObjectFactory() ;

  • Create class instances:

    Library library = factory.createLibrary() ;
    Book bookOne = factory.createBook() ;
    bookOne.setTitle("Design Patterns") ;
    bookOne.setPrice("50.00") ;
    Book bookTwo = factory.createBook() ;
    bookTwo.setTitle("Analysis Patterns") ;
    bookTwo.setPrice("45.00") ;
    library.add(bookOne) ;
    library.add(bookTwo);

  • Create an instance of the Marshaller object (from JAXBContext object instance as in scenario 1):

    Marshaller marshaller = jContext.createMarshaller() ;

  • Marshal the Java object tree to an XML document:

    marshaller.marshal(library, new FileOutputStream("library.xml")) ;

    JAXB Customizations
    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:

  • Global: A customization defined with the <globalBindings> element has a global scope applicable to all schema elements and all other schemas that are imported into the schema in which this customization is defined.
  • Schema: A customization defined with a <schemaBindings> element has a schema scope and is only applicable to the schema in which the customization is defined.
  • Definition: A customization value in binding declarations of a type definition and global declaration has definition scope, which covers all schema elements that reference the type definition or the global declaration.
  • Component: A customization value in a binding declaration has component scope if the customization value applies only to the schema element that was annotated with the binding declaration.

    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.

    Summary
    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!

    Resources

  • JAXB User's Guide: http://java.sun.com/xml/jaxb/users-guide/jaxb-using.html
  • JAXB Specification: http://java.sun.com/xml/downloads/jaxb.html
  • JAXB API Specification: http://java.sun.com/webservices/docs/1.3/api/index.html
  • JAXB Reference Implementation: http://java.sun.com/webservices/downloads/webservicespack.html

    (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.)

  • More Stories By Tilak Mitra

    Tilak Mitra is a Certified Senior IT Architect at IBM. He specializes in mid- to large-range enterprise and application architectures based on J2EE, MQ, and other EAI technologies. You can reach him at [email protected]

    Comments (0)

    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.


    @ThingsExpo Stories
    Nordstrom is transforming the way that they do business and the cloud is the key to enabling speed and hyper personalized customer experiences. In his session at 21st Cloud Expo, Ken Schow, VP of Engineering at Nordstrom, discussed some of the key learnings and common pitfalls of large enterprises moving to the cloud. This includes strategies around choosing a cloud provider(s), architecture, and lessons learned. In addition, he covered some of the best practices for structured team migration an...
    Recently, REAN Cloud built a digital concierge for a North Carolina hospital that had observed that most patient call button questions were repetitive. In addition, the paper-based process used to measure patient health metrics was laborious, not in real-time and sometimes error-prone. In their session at 21st Cloud Expo, Sean Finnerty, Executive Director, Practice Lead, Health Care & Life Science at REAN Cloud, and Dr. S.P.T. Krishnan, Principal Architect at REAN Cloud, discussed how they built...
    In his session at 21st Cloud Expo, Raju Shreewastava, founder of Big Data Trunk, provided a fun and simple way to introduce Machine Leaning to anyone and everyone. He solved a machine learning problem and demonstrated an easy way to be able to do machine learning without even coding. Raju Shreewastava is the founder of Big Data Trunk (www.BigDataTrunk.com), a Big Data Training and consulting firm with offices in the United States. He previously led the data warehouse/business intelligence and B...
    In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, led attendees through the exciting evolution of the cloud. He looked at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering m...
    With tough new regulations coming to Europe on data privacy in May 2018, Calligo will explain why in reality the effect is global and transforms how you consider critical data. EU GDPR fundamentally rewrites the rules for cloud, Big Data and IoT. In his session at 21st Cloud Expo, Adam Ryan, Vice President and General Manager EMEA at Calligo, examined the regulations and provided insight on how it affects technology, challenges the established rules and will usher in new levels of diligence arou...
    The 22nd International Cloud Expo | 1st DXWorld Expo has announced that its Call for Papers is open. Cloud Expo | DXWorld Expo, to be held June 5-7, 2018, at the Javits Center in New York, NY, brings together Cloud Computing, Digital Transformation, Big Data, Internet of Things, DevOps, Machine Learning 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 busin...
    Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
    No hype cycles or predictions of a gazillion things here. IoT is here. You get it. You know your business and have great ideas for a business transformation strategy. What comes next? Time to make it happen. In his session at @ThingsExpo, Jay Mason, an Associate Partner of Analytics, IoT & Cybersecurity at M&S Consulting, presented a step-by-step plan to develop your technology implementation strategy. He also discussed the evaluation of communication standards and IoT messaging protocols, data...
    22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
    22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
    DevOps at Cloud Expo – being held June 5-7, 2018, at the Javits Center in New York, NY – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's largest enterprises – and delivering real results. Among the proven benefits,...
    @DevOpsSummit at Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, is co-located with 22nd Cloud Expo | 1st DXWorld Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. 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...
    Cloud Expo | DXWorld Expo have announced the conference tracks for Cloud Expo 2018. Cloud Expo will be held June 5-7, 2018, at the Javits Center in New York City, and November 6-8, 2018, at the Santa Clara Convention Center, Santa Clara, CA. Digital Transformation (DX) is a major focus with the introduction of DX Expo within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive ov...
    SYS-CON Events announced today that T-Mobile exhibited 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 qua...
    SYS-CON Events announced today that Cedexis will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Cedexis is the leader in data-driven enterprise global traffic management. Whether optimizing traffic through datacenters, clouds, CDNs, or any combination, Cedexis solutions drive quality and cost-effectiveness. For more information, please visit https://www.cedexis.com.
    SYS-CON Events announced today that Google Cloud has been named “Keynote Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Companies come to Google Cloud to transform their businesses. Google Cloud’s comprehensive portfolio – from infrastructure to apps to devices – helps enterprises innovate faster, scale smarter, stay secure, and do more with data than ever before.
    SYS-CON Events announced today that Vivint to exhibit at SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California. As a leading smart home technology provider, Vivint offers home security, energy management, home automation, local cloud storage, and high-speed Internet solutions to more than one million customers throughout the United States and Canada. The end result is a smart home solution that sav...
    SYS-CON Events announced today that Opsani will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Opsani is the leading provider of deployment automation systems for running and scaling traditional enterprise applications on container infrastructure.
    SYS-CON Events announced today that Nirmata will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Nirmata provides a comprehensive platform, for deploying, operating, and optimizing containerized applications across clouds, powered by Kubernetes. Nirmata empowers enterprise DevOps teams by fully automating the complex operations and management of application containers and its underlying ...
    SYS-CON Events announced today that Opsani to exhibit at SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California. Opsani is creating the next generation of automated continuous deployment tools designed specifically for containers. How is continuous deployment different from continuous integration and continuous delivery? CI/CD tools provide build and test. Continuous Deployment is the means by which...