|By Tilak Mitra||
|March 30, 2004 12:00 AM EST||
JAXB (Java Architecture for XML Binding) provides a convenient way to bind an XML Schema to a representation in Java code and makes it easy for developers to incorporate XML data and processing functions into applications based on Java technology without having to know much about XML itself.
It has been proven over the past few years that the best form of information exchange (in a typical B2B or B2C scenario) is through XML. There are various XML-based standards (schemas) for both the horizontal and vertical market sectors, and there are ongoing efforts to move toward a standardized format.
With the proliferation of XML-based information exchange, the industry will write lots of Java code to consume XML Schema-based documents. JAXB (Java Architecture for XML Binding) provides a convenient way to bind an XML Schema to a representation in Java code. This makes it easy for developers to incorporate XML data and processing functions in applications based on Java technology without having to know much about XML itself.
This article will show developers how to utilize the power, ease, and flexibility of JAXB from within the WebSphere Studio Application Developer (referred to as WebSphere Studio), while developing real-world enterprise applications. With JAXB, developers no longer need to learn the intricacies of XML parsing techniques!
What You Need to Know
Although developers need not worry about XML parsing techniques anymore, they may need to do some reading up.
JAXB is built upon XML Schema, so a sound understanding of XML Schema is imperative in order to harness the power of JAXB. Business domain objects and their structural relationships can be well represented through an XML Schema, provided you have a good understanding of its power. The essence of JAXB lies in its customization of the XML Schema for Java objects. These customizations follow the rules of XML Schema. Adding JAXB customizations to a business domain object model (represented in XML Schema) is simple once the hard work of creating the schema is accomplished.
This article assumes you understand:
- XML Schemas (the more detailed the better)
- WebSphere Studio 5.1
You must have the following products to complete the steps in this article:
- WebSphere Studio Application Developer 5.1
- Java Web Services Developer's Pack (JWSDP v1.3)
JWSDP from Sun Microsystems is a free integrated toolkit you can use to build, test, and deploy XML applications, Web services, and Web applications with the latest Web services technologies and standards implementations. JAXB is an essential part of this package. JWSDP 1.3 must be downloaded and installed (see the Development Environment Setup section for a detailed explanation of the process).
In object-oriented programming (OOP) there are two pivotal concepts: classes and objects. Classes provide the structure for software concepts or entities, whereas objects are live instances of the classes. A similar analogy can be used in XML representation. An XML Schema can be conceptualized as the allowable structure and constructs that can be used in the creation of an XML document (which conforms to the schema). The schema (in XML) and classes (in OOP) are the conceptual building blocks, whereas documents (in XML) and objects (in OOP) are live instances that conform to their respective conceptual building blocks.
Working with Java objects and classes is fundamentally different from working with XML. JAXB brings in the idea of data binding, which creates a correspondence between the XML schemas and the Java classes, and then utilizes the mapping to convert XML documents to and from Java classes. The JAXB schema compiler creates Java classes and interfaces based on the structure of the XML Schema. JAXB libraries are used in marshaling and unmarshaling. Marshaling is the process of turning one or more Java objects into an XML document, whereas unmarshaling is the reverse process - creating a Java object from an XML document.
To use JAXB in a Java application the first step is to run the JAXB compiler (XJC) to create the Java classes and interfaces. For every element in the XML Schema, one or two Java interfaces and corresponding implementation classes (which implement the interfaces) are generated. The implementation classes are generated in a package that is separate from the one in which the interfaces are generated. Other than the interfaces and the implementation classes, JAXB-specific classes are generated to perform marshaling and unmarshaling, and to create instances of the implementation classes, among other things. (Note: The implementation classes are only instantiated through a factory class generated by the JAXB compiler). The two classes that are primarily used in working with JAXB-created Java objects are:
- JAXBContext: Used for marshaling, unmarshaling, and validating XML documents
- ObjectFactory: Used to instantiate the various implementation classes
The first step is to download and install the JWSDP. As a part of JWSDP, the JAXB compile and runtime libraries and executables are installed. The next step is to download the JAXBTestEAR.zip file from www.sys-con.com/websphere/sourcec.cfm and extract the contents into the C:\temp folder. Next, create a new workspace and import the JAXBTestEAR file:
- Create a folder called JAXB and another called workspace under JAXB in the C:\ drive.
- Open WebSphere Studio and point the workspace to C:\JAXB\workspace.
- Select File>Import from the WebSphere Studio menu.
- Select the EAR file type to import (see Figure 1).
- Browse the file system and select the JAXBTestEAR.ear file. Click Finish.
- The imported project in the J2EE Perspectives, Project Navigator tab should look like Figure 2.
- Select External Tools from the WebSphere Studio menu as shown in Figure 3.
- Click New to create a new configuration. In the Main tab, key in the Name, Location, Working Directory, and Arguments as shown in Figure 4. (Browse the File system and Workspace in order to obtain the values.)
- Switch to the Resource tab and check the checkboxes. Highlight the $resource Scope Variable and then choose JAXBTest as the specific resource.
- Click Apply to save the configurations. Click Run to run the JAXB compiler (xjc.bat) and generate the Java classes and interfaces. The output in the output console will resemble Figure 5.
The example we will develop is a simple GUI menuing system. A widget is a conceptual element that defines the whole set of drawing components that constitute a graphical user interface. Examples of widgets are rectangles, squares, circles, and any other drawable visual component. Our simplistic GUI consists of three visual components in the form of rectangles, squares, and circles. The Widgets component encapsulates a list of the visual components (rectangles, squares, and circles) in any random order. A client can construct the visual components from a given XML document and then retrieve the details of each visual component (to be used in any way the client requires).
Listing 1 illustrates the XML Schema (for the example scenario) in some detail. The xs:annotation element is a container for the xs:appinfo and xs:documentation elements, which contain additional information. These two elements are dedicated to holding machine-processable (xs:appinfo) information and human-readable documentation (xs:documentation).
The section highlighted in blue denotes the JAXB-specific global customizations of the schema that are applicable to the entire schema file. The section highlighted in red denotes the JAXB-specific customizations in which the package where the generated files will be placed is defined (in this case, com.ibm.domainobjects).
In the globalBindings section the collectionType = java.util.ArrayList is highlighted in blue. It denotes that any Collections that are created inside the Java objects all conform to the List interface in Java and are actual instances of ArrayList.
The xjc:serializable element makes sure that all the generated classes are serializable. (This is particularly important when objects are sent and received over the wire while data transfer between various application tiers is performed.)
A superClass called Shape is also defined. This denotes that all the elements defined in this schema have a common superclass called Shape. I show this here in order to illustrate that the classes that are created from the schema can also refer to external classes, i.e., classes that are not created by the JAXB compiler.
The definition of the Widgets element shows that there is a property called "Widgets" that is defined. Had this property not been defined, the binding compiler would have autogenerated a name for the list of choices (for the rectangles, squares, and circles). The autogeneration usually takes the names of the subelements and combines them with "Or". Hence the accessor name for the list would have been something like:
Clearly this is not meaningful. The jxb:property name="Widgets" denotes that the accessor method will be getWidgets, which is clearly much more intuitive than the autogenerated name.
In the example, I will demonstrate:
- How to set up the usage of the external JAXB compiler from WebSphere Studio
- How to use the JAXB compiler to generate Java interfaces and classes
- How to create the Java classes from an XML document
- How to instantiate Java classes, set their attributes, and then generate the corresponding XML document (the reverse of the previous step)
Using the JAXB Generated Classes
The JAXB compiler is run only once. There is no need to run it again if the schema is not changed. However, if the schema undergoes any changes, then the JAXB compiler preprocessing step must be executed again in order to regenerate the Java interfaces and classes. In this event, it is advisable to delete all of the generated classes from a previous run of the JAXB compiler before running this step again. This is particularly helpful in cases in which elements in the schema are deleted. The generated classes from the new run of the compiler do not delete the old generated classes and hence some unused classes from the previous version of the schema will be left behind.
Once all the classes are generated, the fun begins, with the bulk of the tedious (if you consider it so) setup work already completed. It is time to use the generated classes in order to convert XML documents into Java classes and vice versa. We will concentrate on a client class called JAXBTester. This class demonstrates two activities. It first reads in a given XML document from which it creates the Java object structure/tree.
Analysis of JAXBTester
JAXBTester has three methods. A brief explanation of each of the methods is in order.
Notice how not a single line of XML-specific code needs to be coded by the developer; the specifics of the conversion are all contained inside the generated classes.
Running the Sample
Before running the client class several steps must be followed in sequence:
- The JAXB compiler must be run to generate the Java object tree. (This step should already have been completed.)
- The import statements that are commented out in the JAXBTester must be uncommented. The method bodies of unmarshallIt and marshallIt that are commented out need to be uncommented prior to compilation of JAXBTester. These portions are commented out because the classes that are referenced (both in the import statements and inside the methods) are all generated classes. When the EAR file was imported, these generated classes did not exist; hence, prior to Step 1 JAXBTester would not have compiled.
- The value of the absPathToXML, which denotes the path to the schema.xml file, must be changed (if required) to reflect the path to the file in the file system.
This article introduced you to the basics of JAXB. The most important aspect of this article was the demonstration of how JAXB can be used in a J2EE application and how the all development can be achieved from our friendly and most loved IDE - WebSphere Studio.
The best way to learn JAXB is to get very familiar and comfortable with XML Schema and then learn the tricks of JAXB customizations. The best way to learn XML Schema is to read a book on it, and then apply the concepts in real-world scenarios, exploiting the various features. (The O'Reilly book XML Schema is my favorite.)
SYS-CON Events announced today that Fusion, a leading provider of cloud services, will exhibit at 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. Fusion, a leading provider of integrated cloud solutions to small, medium and large businesses, is the industry's single source for the cloud. Fusion's advanced, proprietary cloud service platform enables the integration of leading edge solutions in the cloud, including clou...
Feb. 6, 2016 03:30 PM EST Reads: 698
With the Apple Watch making its way onto wrists all over the world, it’s only a matter of time before it becomes a staple in the workplace. In fact, Forrester reported that 68 percent of technology and business decision-makers characterize wearables as a top priority for 2015. Recognizing their business value early on, FinancialForce.com was the first to bring ERP to wearables, helping streamline communication across front and back office functions. In his session at @ThingsExpo, Kevin Roberts...
Feb. 6, 2016 03:15 PM EST Reads: 316
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze 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, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
Feb. 6, 2016 02:30 PM EST Reads: 342
SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, will exhibit at 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. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...
Feb. 6, 2016 01:30 PM EST Reads: 328
SYS-CON Events announced today that VAI, a leading ERP software provider, will exhibit at 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. VAI (Vormittag Associates, Inc.) is a leading independent mid-market ERP software developer renowned for its flexible solutions and ability to automate critical business functions for the distribution, manufacturing, specialty retail and service sectors. An IBM Premier Business Part...
Feb. 6, 2016 01:00 PM EST Reads: 528
The cloud promises new levels of agility and cost-savings for Big Data, data warehousing and analytics. But it’s challenging to understand all the options – from IaaS and PaaS to newer services like HaaS (Hadoop as a Service) and BDaaS (Big Data as a Service). In her session at @BigDataExpo at @ThingsExpo, Hannah Smalltree, a director at Cazena, will provide an educational overview of emerging “as-a-service” options for Big Data in the cloud. This is critical background for IT and data profes...
Feb. 6, 2016 11:00 AM EST Reads: 103
With an estimated 50 billion devices connected to the Internet by 2020, several industries will begin to expand their capabilities for retaining end point data at the edge to better utilize the range of data types and sheer volume of M2M data generated by the Internet of Things. In his session at @ThingsExpo, Don DeLoach, CEO and President of Infobright, will discuss the infrastructures businesses will need to implement to handle this explosion of data by providing specific use cases for filte...
Feb. 6, 2016 11:00 AM EST
Fortunately, meaningful and tangible business cases for IoT are plentiful in a broad array of industries and vertical markets. These range from simple warranty cost reduction for capital intensive assets, to minimizing downtime for vital business tools, to creating feedback loops improving product design, to improving and enhancing enterprise customer experiences. All of these business cases, which will be briefly explored in this session, hinge on cost effectively extracting relevant data from ...
Feb. 6, 2016 09:00 AM EST
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 18th Cloud Expo, which will take place on June 7-9, 2015 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 ad...
Feb. 6, 2016 05:00 AM EST Reads: 323
Most people haven’t heard the word, “gamification,” even though they probably, and perhaps unwittingly, participate in it every day. Gamification is “the process of adding games or game-like elements to something (as a task) so as to encourage participation.” Further, gamification is about bringing game mechanics – rules, constructs, processes, and methods – into the real world in an effort to engage people. In his session at @ThingsExpo, Robert Endo, owner and engagement manager of Intrepid D...
Feb. 5, 2016 09:00 PM EST Reads: 763
As enterprises work to take advantage of Big Data technologies, they frequently become distracted by product-level decisions. In most new Big Data builds this approach is completely counter-productive: it presupposes tools that may not be a fit for development teams, forces IT to take on the burden of evaluating and maintaining unfamiliar technology, and represents a major up-front expense. In his session at @BigDataExpo at @ThingsExpo, Andrew Warfield, CTO and Co-Founder of Coho Data, will dis...
Feb. 5, 2016 10:00 AM EST
Eighty percent of a data scientist’s time is spent gathering and cleaning up data, and 80% of all data is unstructured and almost never analyzed. Cognitive computing, in combination with Big Data, is changing the equation by creating data reservoirs and using natural language processing to enable analysis of unstructured data sources. This is impacting every aspect of the analytics profession from how data is mined (and by whom) to how it is delivered. This is not some futuristic vision: it's ha...
Feb. 2, 2016 02:00 PM EST Reads: 399
WebRTC has had a real tough three or four years, and so have those working with it. Only a few short years ago, the development world were excited about WebRTC and proclaiming how awesome it was. You might have played with the technology a couple of years ago, only to find the extra infrastructure requirements were painful to implement and poorly documented. This probably left a bitter taste in your mouth, especially when things went wrong.
Feb. 2, 2016 04:30 AM EST Reads: 832
Learn how IoT, cloud, social networks and last but not least, humans, can be integrated into a seamless integration of cooperative organisms both cybernetic and biological. This has been enabled by recent advances in IoT device capabilities, messaging frameworks, presence and collaboration services, where devices can share information and make independent and human assisted decisions based upon social status from other entities. In his session at @ThingsExpo, Michael Heydt, founder of Seamless...
Feb. 1, 2016 05:00 AM EST Reads: 915
The IoT's basic concept of collecting data from as many sources possible to drive better decision making, create process innovation and realize additional revenue has been in use at large enterprises with deep pockets for decades. So what has changed? In his session at @ThingsExpo, Prasanna Sivaramakrishnan, Solutions Architect at Red Hat, discussed the impact commodity hardware, ubiquitous connectivity, and innovations in open source software are having on the connected universe of people, thi...
Jan. 31, 2016 09:00 PM EST Reads: 712
WebRTC: together these advances have created a perfect storm of technologies that are disrupting and transforming classic communications models and ecosystems. In his session at WebRTC Summit, Cary Bran, VP of Innovation and New Ventures at Plantronics and PLT Labs, provided an overview of this technological shift, including associated business and consumer communications impacts, and opportunities it may enable, complement or entirely transform.
Jan. 31, 2016 07:15 PM EST Reads: 1,132
There are so many tools and techniques for data analytics that even for a data scientist the choices, possible systems, and even the types of data can be daunting. In his session at @ThingsExpo, Chris Harrold, Global CTO for Big Data Solutions for EMC Corporation, showed how to perform a simple, but meaningful analysis of social sentiment data using freely available tools that take only minutes to download and install. Participants received the download information, scripts, and complete end-t...
Jan. 31, 2016 10:00 AM EST Reads: 1,190
For manufacturers, the Internet of Things (IoT) represents a jumping-off point for innovation, jobs, and revenue creation. But to adequately seize the opportunity, manufacturers must design devices that are interconnected, can continually sense their environment and process huge amounts of data. As a first step, manufacturers must embrace a new product development ecosystem in order to support these products.
Jan. 31, 2016 10:00 AM EST Reads: 790
Manufacturing connected IoT versions of traditional products requires more than multiple deep technology skills. It also requires a shift in mindset, to realize that connected, sensor-enabled “things” act more like services than what we usually think of as products. In his session at @ThingsExpo, David Friedman, CEO and co-founder of Ayla Networks, discussed how when sensors start generating detailed real-world data about products and how they’re being used, smart manufacturers can use the dat...
Jan. 30, 2016 07:45 PM EST Reads: 757
When it comes to IoT in the enterprise, namely the commercial building and hospitality markets, a benefit not getting the attention it deserves is energy efficiency, and IoT’s direct impact on a cleaner, greener environment when installed in smart buildings. Until now clean technology was offered piecemeal and led with point solutions that require significant systems integration to orchestrate and deploy. There didn't exist a 'top down' approach that can manage and monitor the way a Smart Buildi...
Jan. 30, 2016 03:45 PM EST Reads: 1,254