|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.)
Almost two-thirds of companies either have or soon will have IoT as the backbone of their business in 2016. However, IoT is far more complex than most firms expected. How can you not get trapped in the pitfalls? In his session at @ThingsExpo, Tony Shan, a renowned visionary and thought leader, will introduce a holistic method of IoTification, which is the process of IoTifying the existing technology and business models to adopt and leverage IoT. He will drill down to the components in this fra...
Aug. 30, 2016 10:30 AM EDT Reads: 375
Data is an unusual currency; it is not restricted by the same transactional limitations as money or people. In fact, the more that you leverage your data across multiple business use cases, the more valuable it becomes to the organization. And the same can be said about the organization’s analytics. In his session at 19th Cloud Expo, Bill Schmarzo, CTO for the Big Data Practice at EMC, will introduce a methodology for capturing, enriching and sharing data (and analytics) across the organizati...
Aug. 30, 2016 09:08 AM EDT Reads: 171
Why do your mobile transformations need to happen today? Mobile is the strategy that enterprise transformation centers on to drive customer engagement. In his general session at @ThingsExpo, Roger Woods, Director, Mobile Product & Strategy – Adobe Marketing Cloud, covered key IoT and mobile trends that are forcing mobile transformation, key components of a solid mobile strategy and explored how brands are effectively driving mobile change throughout the enterprise.
Aug. 30, 2016 03:45 AM EDT Reads: 514
With so much going on in this space you could be forgiven for thinking you were always working with yesterday’s technologies. So much change, so quickly. What do you do if you have to build a solution from the ground up that is expected to live in the field for at least 5-10 years? This is the challenge we faced when we looked to refresh our existing 10-year-old custom hardware stack to measure the fullness of trash cans and compactors.
Aug. 30, 2016 02:30 AM EDT Reads: 1,861
The emerging Internet of Everything creates tremendous new opportunities for customer engagement and business model innovation. However, enterprises must overcome a number of critical challenges to bring these new solutions to market. In his session at @ThingsExpo, Michael Martin, CTO/CIO at nfrastructure, outlined these key challenges and recommended approaches for overcoming them to achieve speed and agility in the design, development and implementation of Internet of Everything solutions wi...
Aug. 30, 2016 02:00 AM EDT Reads: 2,248
Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is expected in the amount of information being processed, managed, analyzed, and acted upon by enterprise IT. This amazing is not part of some distant future - it is happening today. One report shows a 650% increase in enterprise data by 2020. Other estimates are even higher....
Aug. 30, 2016 01:30 AM EDT Reads: 3,053
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 business becomes digital the more stakeholders are interested in this data including how it relates to business. Some of these people have never used a monitoring tool before. They have a question on their mind like “How is my application doing” but no id...
Aug. 30, 2016 01:00 AM EDT Reads: 1,942
Smart Cities are here to stay, but for their promise to be delivered, the data they produce must not be put in new siloes. In his session at @ThingsExpo, Mathias Herberts, Co-founder and CTO of Cityzen Data, will deep dive into best practices that will ensure a successful smart city journey.
Aug. 30, 2016 12:00 AM EDT Reads: 1,678
DevOps at Cloud Expo, taking place Nov 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud 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 for long dev...
Aug. 29, 2016 10:00 PM EDT Reads: 2,496
Identity is in everything and customers are looking to their providers to ensure the security of their identities, transactions and data. With the increased reliance on cloud-based services, service providers must build security and trust into their offerings, adding value to customers and improving the user experience. Making identity, security and privacy easy for customers provides a unique advantage over the competition.
Aug. 29, 2016 08:30 PM EDT Reads: 2,453
SYS-CON Events announced today that 910Telecom will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Housed in the classic Denver Gas & Electric Building, 910 15th St., 910Telecom is a carrier-neutral telecom hotel located in the heart of Denver. Adjacent to CenturyLink, AT&T, and Denver Main, 910Telecom offers connectivity to all major carriers, Internet service providers, Internet backbones and ...
Aug. 29, 2016 07:00 PM EDT Reads: 1,989
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices - comp...
Aug. 29, 2016 02:15 PM EDT Reads: 3,751
Data is the fuel that drives the machine learning algorithmic engines and ultimately provides the business value. In his session at Cloud Expo, Ed Featherston, a director and senior enterprise architect at Collaborative Consulting, will discuss the key considerations around quality, volume, timeliness, and pedigree that must be dealt with in order to properly fuel that engine.
Aug. 29, 2016 12:45 PM EDT Reads: 2,043
There is growing need for data-driven applications and the need for digital platforms to build these apps. In his session at 19th Cloud Expo, Muddu Sudhakar, VP and GM of Security & IoT at Splunk, will cover different PaaS solutions and Big Data platforms that are available to build applications. In addition, AI and machine learning are creating new requirements that developers need in the building of next-gen apps. The next-generation digital platforms have some of the past platform needs a...
Aug. 29, 2016 12:15 PM EDT Reads: 887
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, 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 strategy. Meanwhile, 94% of enterpri...
Aug. 29, 2016 12:00 PM EDT Reads: 3,210
SYS-CON Events announced today Telecom Reseller has been named “Media Sponsor” of SYS-CON's 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.
Aug. 29, 2016 08:00 AM EDT Reads: 990
Pulzze Systems was happy to participate in such a premier event and thankful to be receiving the winning investment and global network support from G-Startup Worldwide. It is an exciting time for Pulzze to showcase the effectiveness of innovative technologies and enable them to make the world smarter and better. The reputable contest is held to identify promising startups around the globe that are assured to change the world through their innovative products and disruptive technologies. There w...
Aug. 29, 2016 07:30 AM EDT Reads: 843
The 19th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Digital Transformation, Microservices 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 business opportuni...
Aug. 28, 2016 10:30 PM EDT Reads: 4,089
I wanted to gather all of my Internet of Things (IOT) blogs into a single blog (that I could later use with my University of San Francisco (USF) Big Data “MBA” course). However as I started to pull these blogs together, I realized that my IOT discussion lacked a vision; it lacked an end point towards which an organization could drive their IOT envisioning, proof of value, app dev, data engineering and data science efforts. And I think that the IOT end point is really quite simple…
Aug. 27, 2016 12:45 PM EDT Reads: 2,417
Personalization has long been the holy grail of marketing. Simply stated, communicate the most relevant offer to the right person and you will increase sales. To achieve this, you must understand the individual. Consequently, digital marketers developed many ways to gather and leverage customer information to deliver targeted experiences. In his session at @ThingsExpo, Lou Casal, Founder and Principal Consultant at Practicala, discussed how the Internet of Things (IoT) has accelerated our abil...
Aug. 27, 2016 02:30 AM EDT Reads: 2,111