Click here to close now.


IoT User Interface Authors: Elizabeth White, AppDynamics Blog, Gary Kaiser, Pat Romanski, Liz McMillan

Related Topics: Industrial IoT

Industrial IoT: Article

An Introduction to JDOM Part 2 of 2

An Introduction to JDOM Part 2 of 2

This second of a two-part series on JDOM examines in greater detail what it takes to use JDOM to perform some common tasks. In particular, I'll illustrate how to create JDOM documents, read JDOM documents from various sources (including SAX and DOM), output to various sources, and how to use JDOM with XSLT.

The overview of JDOM discussed in Part 1 (XML-J, Vol. 2, issue 7) revealed that JDOM bridges the gap between inconsistencies in DOM parser APIs via adapters. It also takes SAX and DOM to the next level in terms of ease of use, by compensating for the weaknesses of these APIs when it comes to XML document manipulation.

Part 1 explored the JDOM API and the packages and classes that are most significant for developing in JDOM. The main components of a JDOM document that were defined in Part 1 are critical prerequisites for understanding this article.

Creating a JDOM Document
JDOM documents can be created in two ways - from scratch or from some other input source, such as an XML document, a series of SAX events, or a DOM document. First, we'll discuss how to create a JDOM document in memory from scratch, and then, in the next section, we'll address how to output that document in various different formats.

After we create a JDOM document and show how to output its content, we will demonstrate how to input an existing XML document, a series of SAX events, or a DOM document, and convert it into a JDOM document, which is the second option for creating a JDOM document.

Creating a JDOM Document in Memory
Let's begin by creating a JDOM document in memory, from scratch. Since JDOM was written with the Java developer in mind (keeping as close to Java standards as possible), creating a new JDOM document in memory is straightforward for Java developers.

To create a JDOM document in memory using the core JDOM classes, Document and Element from the org.jdom package, use the following code:

Document doc = new Document( new

.setText("Hello World!") );

This creates, in memory, a bare bones JDOM document and stores it in the variable doc. That's all there is to it. Next, we'll look at outputting this document to the screen, so we can see what it looks like in XML.

Outputting JDOM Documents
After creating a JDOM document, it can be output using one of three primary ways:

1. org.jdom.output.DOMOutputter: As a DOM document
2. org.jdom.output.SAXOutputter:  As a sequence of SAX events
3. org.jdom.output.XMLOutputter: As an XML document to a file or an output stream

As part of the org.jdom.output package, XMLOutputter outputs a JDOM document to an output stream, such as the screen, or to a file. Alternatively, the SAXOutputter or DOMOutputter classes, also of the org.jdom.output package, can be used to output the JDOM document as a series of SAX events or as a DOM document, respectively.

In Listing 1, we illustrate output using XMLOutputter to output to the standard output stream, System.out, which by default is the screen when running in a DOS/UNIX command window.

Using XMLOutputter
When a JDOM document is output as an XML document, it's output as one or two long lines of XML code unless you specify otherwise. This is fine if it's being sent to another application or system for processing, and is actually the most compact. However, it makes it very difficult to read and see the structure.

To format the XML output to improve readability - by humans, not computers - we can specify a couple of parameters when creating the XMLOutputter. The first parameter defines the level of indentation - usually as a sequence of spaces - and the second is a Boolean value that, if set to true, causes new lines to be added to the output.

Here's an example:

outputter = new XMLOutputter(" ",
outputter.output(doc, System.out);

We use this approach in our HelloWorld example shown later in the article.

Note that since XMLOutputter contains methods to output a JDOM document to a as well as to a, you can use the same approach whether outputting to a file, an output stream (such as across a network), to the screen, or to any other form of Writer or OutputStream.

Other output methods in XMLOutputter allow you to output just parts of the JDOM document such as CDATA sections, comments, elements, entities, and processing instructions. We talked about each of these components in Part 1.

The JDOM document created as described in the last example will be output to the screen. The code required is in Listing 1.

To compile this file, first ensure that you have set up your Java environment correctly for use with JDOM. Your CLASSPATH must include the xerces.jar file found in the lib subdirectory of your JDOM distribution. The xerces.jar file should be followed in the CLASSPATH by the jdom.jar file from the build subdirectory of your JDOM distribution.

Next, to compile the file, type the following code:


After the file compiles, run the HelloWorld application using:

java HelloWorld

This produces the following output:

<?xml version="1.0" encoding="UTF-8"?> <root-element>Hello World!</root-element>

The root-element tag is from the code defined in the file, specifically from the line that instantiates a new Element. Here is the code that defines the name of the new Element.

new Element("root-element")

The text "Hello World!" also was defined in the code in the file and by the call to the setText method. The following code defines the text for the root element:

new Element("root-element").setText("Hello World!")

As you can see, using JDOM, it's possible to produce perfectly valid XML output with little prior knowledge of XML. This was one of the original goals of JDOM.

Outputting Using DOMOutputter
We just saw how to output a JDOM document as an XML file. Using DOMOutputter, we can output a JDOM document as a DOM document. This is useful when interfacing with another application or system that expects a DOM document as its input.

The following lines of code show how to create and use DOMOutputter to output a JDOM document, doc.

DOMOutputter outputter = new DOMOutputter(); outputter.output( doc );

In addition to outputting JDOM documents, DOMOutputter also provides methods that allow you to output JDOM elements and attributes. See the JDOM API documentation for details.

Outputting Using SAXOutputter
We just saw how to output a JDOM document as an XML file and as a DOM document. The final way to output a JDOM document is as a sequence of SAX events. This is useful for interfacing with applications or components that handle a series of SAX events.

When constructing a SAXOutputter, you must specify a SAX content handler (actually an org.xml.sax.ContentHandler) as a minimum. You then have the option of specifying a SAX error handler (org.xml.sax.ErrorHandler), DTD handler (org.xml.sax.DTDHandler), and entity handler (org.xml.sax.EntityHandler) after you have created the SAXOutputter object.

The following lines of code show how to create and use SAXOutputter to output a JDOM document, doc.

SAXOutputter outputter = new SAXOutputter( contentHandler ); outputter.output( doc );

After creating a SAXOutputter object, you need to invoke the output() method to pass the JDOM document object you want to output to the outputter.

Inputting to JDOM Documents
Earlier in this article we saw how to create a JDOM document from scratch. Another way of creating a JDOM document is to read an XML document or input stream (using a SAX parser), or input a DOM document. Again, we will use an output stream to output the JDOM document.

To input an XML file, input stream, or DOM document as a JDOM document, use the SAXBuilder or DOMBuilder classes, respectively, from the org.jdom.input package.

Inputting Using SAXBuilder
Perhaps the most common means of building a JDOM document is to use SAXBuilder. SAXBuilder uses a SAX parser to parse an XML input file or input stream. Building a JDOM document using SAXBuilder is a two-step process.

In step one, you need to create a new instance of a SAXBuilder object. Next, invoke one of the build methods for reading the XML input and building a JDOM document object.

Four different constructors are available for creating a new SAXBuilder object, the primary one using the default SAX parser as determined by JAXP. Validation is turned off. It can be enabled and disabled after the construction of a SAXBuilder object by using the setValidation() method.

The other three constructors allow more control over whether or not validation is enabled or disabled and in choosing an alternate SAX parser.

After creating a SAXBuilder object, other methods are available that allow us to initialize it with a custom DTD handler, Entity resolver, XML filter, and error handler.

Once we have instantiated a new SAXBuilder object, we can use it to build a JDOM document. There are seven different publicly accessible build methods available.

The main differences between the seven build methods lie in where the XML input is to come from. It can come from a variety of sources, including one specified by a,,, a URI specified as a java.lang.String, or a

SAX parsers tend to be the first choice over DOM parsers because of their speed when reading in XML and generating a JDOM document. If you prefer not to use the default SAX parser with SAXBuilder, you can always substitute a third-party SAX parser.

Simply pass the name of the SAX Driver class to the SAXBuilder constructor when creating the builder. Make sure that the classes required by the alternate parser are available in your CLASSPATH. SAXBuilder will then use the specified SAX parser to build a JDOM document.

Inputting Using DOMBuilder
An alternative to the SAXBuilder is the DOMBuilder. The DOMBuilder class is intended to allow us to build a JDOM document from a preexisting DOM document. It uses basically the same steps as when using SAXBuilder.

First, create a new instance of a DOMBuilder object. Next, invoke one of the build methods to read the XML input and build a JDOM document object.

To create a new DOMBuilder object, four different constructors are available. The default constructor creates a new DOMBuilder using the default DOM parser - as specified by the default JAXP parser, or a JDOM default if not. Validation is turned off.

The default constructor with no validation suffices for most purposes, but the other three constructors allow for greater control when selecting a DOM parser. They also allow you to enable or disable validation.

After creating a DOMBuilder object, use one of the methods to build a JDOM document from an existing DOM document object. This build method is just like the methods except that it takes an org.w3c.dom.Document object as a single argument for its input.

In addition, DOMBuilder contains a build method that allows you to construct a JDOM element object directly from a DOM element (org.w3c.dom.Element) object. The DOMBuilder class is intended primarily as a way of generating a JDOM document from a preexisting DOM document.

The DOMBuilder class contains three additional methods, each of these taking a single argument - either a,, or a - and building a JDOM document from a file, input stream, or URL, respectively. These other methods are provided as a means of cross-checking the methods, which is the recommended parser for XML parsing.

Generating a JDOM document using a DOM parser is slow, hence the SAX parser recommendation. The only possible exception to not using a SAX parser (via the SAXBuilder class) is if you are trying to validate the correct operation of the SAXBuilder class.

Working Together: JDOM and XSLT
One of the more common questions posted to the JDOM-interest discussion list centers on using JDOM with XSLT. There are several ways to do this. Below we look at one such way using a couple of classes from the JDOM-contrib repository.

Now that we have seen how to create, input, and output a JDOM document object, let's see how to feed it into an XSLT processor to transform one JDOM document into another.

XSLT Transformations Using JDOMResult and JDOMSource
The example described later assumes that you have downloaded and installed the JDOM-contrib files from the JDOM Web site. Refer to Part 1 of this series for details on downloading and installing JDOM. The JDOM-contrib files contain two classes intended to make using JDOM with XSLT quite straightforward. These are JDOMResult and JDOMSource. You can access these, provided the JDOM-contrib.jar file is (or its classes are) in your CLASSPATH.

In addition to the JDOM-contrib files, this example also makes use of classes from the Java API for XML Processing (JAXP) 1.1.

In Listing 2 there's a transform method - in the class XSLTDemo - that takes a JDOM document and the name of an XSLT file, then using JDOMResult and JDOMSource, transforms it according to the instructions in the given XSLT file. The transform method then returns the resulting JDOM document.

I thank Laurent Bihanic for this example, and the contribution of JDOMSource and JDOMResult to the JDOM-contrib repository.

Family Matters: Working with Children
One of the useful features of JDOM is that it allows developers to add and remove elements with a single line of code in its simplest form. For example, developers can create a child element from one line of code instead of requiring a factory method to create it for them after requesting it. However, more business logic may need to be added for greater functionality.

Once you have a JDOM document, you'll want to traverse it and possibly manipulate certain elements. JDOM makes manipulation of child elements as easy as manipulating a Java 2 List. To obtain a list of child Elements belonging to a given element, use one of the getChildren methods:

List children = element.getChildren();
List children = element.getChildren
( name );
List children = element.getChildren
( name, namespace );

These methods return a list of child elements belonging to the Element, element. If no children exist, the returned list will be empty.

Any changes to the returned list object will automatically be reflected in the underlying JDOM document. Since each of these methods return a Java 2 List object, then adding, removing, and reordering children are performed using native Java 2 List operations.

For example, to create a new child Element and add it as the second child to a list, use something like the following:

Element newChild =
new Element("child")
.setText("new child element");
children.add( 1, newChild );

Note that since the first item in a list is numbered 0, then the second item has an index of 1. Hence, the above code adds the newChild element as the second child in the list, children.

Similarly, to remove the first element (index 0) from the list, use the following:

children.remove( 0 );

The change is automatically reflected in the associated JDOM document, and the first child will be removed from the document.

As another JDOM code safety check, JDOM validates the document structure, making sure you don't have duplicate nodes above and below a child, which would result in an infinite loop. In other words, JDOM overrides the add and remove methods and makes sure there's only one parent for each child element and that that same child does not exist in a conflicting position on the tree.

This two-part series on JDOM examined in detail how this open-source Java API simplifies XML document manipulation when compared with the previous alternatives. It also describes how JDOM interacts with existing APIs for document manipulation, such as SAX and DOM. JDOM's tight, Java-centric design makes XML document creation, manipulation, transformation, and parsing a no-brainer for Java developers.

In these articles, we explored the purpose that JDOM serves in filling in the gaps where SAX and DOM fail in XML document manipulation. We also explored the JDOM API in depth, then in Part 2 we demonstrated how to use the API to perform common tasks such as inputting and outputting JDOM documents, as well as how to use JDOM with XSLT.

JDOM recently was accepted as a Java Specification Request (JSR-102) by the Java Community Process (JCP). As such, expect to hear a great deal more about JDOM in the future as it continues to be embraced by the Java community.

Special thanks to Steven Gould for sharing his expertise in JDOM and working so diligently with me on this series.

1. JDOM:
2. JDOM discussion lists:
3. Java API for XML Processing (JAXP):
4. The Collections API for JDK 1.1:
5. For an alternative way of using JDOM with XSLT, see "Using JDOM and XSLT: How to Find the Right Input for Your Processor," IBM developerWorks, March 2001, by Brett McLaughlin (

More Stories By Shari Jones

Shari Jones is a freelance journalist and a technical writer. A former consultant, she has more than 10 years of experience writing technical articles and documentation - covering all areas of the high-tech industry. She has written for various magazines, including SunWorld,, IBM's developerWorks and others. Her work also has been selected for inclusion on Sun's Solaris Developer Connection.

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.

@CloudExpo Stories
Containers are revolutionizing the way we deploy and maintain our infrastructures, but monitoring and troubleshooting in a containerized environment can still be painful and impractical. Understanding even basic resource usage is difficult - let alone tracking network connections or malicious activity. In his session at DevOps Summit, Gianluca Borello, Sr. Software Engineer at Sysdig, will cover the current state of the art for container monitoring and visibility, including pros / cons and li...
The web app is agile. The REST API is agile. The testing and planning are agile. But alas, data infrastructures certainly are not. Once an application matures, changing the shape or indexing scheme of data often forces at best a top down planning exercise and at worst includes schema changes that force downtime. The time has come for a new approach that fundamentally advances the agility of distributed data infrastructures. Come learn about a new solution to the problems faced by software organ...
The buzz continues for cloud, data analytics and the Internet of Things (IoT) and their collective impact across all industries. But a new conversation is emerging - how do companies use industry disruption and technology enablers to lead in markets undergoing change, uncertainty and ambiguity? Organizations of all sizes need to evolve and transform, often under massive pressure, as industry lines blur and merge and traditional business models are assaulted and turned upside down. In this new da...
Achim Weiss is Chief Executive Officer and co-founder of ProfitBricks. In 1995, he broke off his studies to co-found the web hosting company "Schlund+Partner." The company "Schlund+Partner" later became the 1&1 web hosting product line. From 1995 to 2008, he was the technical director for several important projects: the largest web hosting platform in the world, the second largest DSL platform, a video on-demand delivery network, the largest eMail backend in Europe, and a universal billing syste...
Today air travel is a minefield of delays, hassles and customer disappointment. Airlines struggle to revitalize the experience. GE and M2Mi will demonstrate practical examples of how IoT solutions are helping airlines bring back personalization, reduce trip time and improve reliability. In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect with GE, and Dr. Sarah Cooper, M2Mi's VP Business Development and Engineering, will explore the IoT cloud-based platform technologies driv...
There are many considerations when moving applications from on-premise to cloud. It is critical to understand the benefits and also challenges of this migration. A successful migration will result in lower Total Cost of Ownership, yet offer the same or higher level of robustness. Migration to cloud shifts computing resources from your data center, which can yield significant advantages provided that the cloud vendor an offer enterprise-grade quality for your application.
"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 interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Containers have changed the mind of IT in DevOps. They enable developers to work with dev, test, stage and production environments identically. Containers provide the right abstraction for microservices and many cloud platforms have integrated them into deployment pipelines. DevOps and Containers together help companies to achieve their business goals faster and more effectively.
WebRTC converts the entire network into a ubiquitous communications cloud thereby connecting anytime, anywhere through any point. In his session at WebRTC Summit,, Mark Castleman, EIR at Bell Labs and Head of Future X Labs, will discuss how the transformational nature of communications is achieved through the democratizing force of WebRTC. WebRTC is doing for voice what HTML did for web content.
The IoT is upon us, but today’s databases, built on 30-year-old math, require multiple platforms to create a single solution. Data demands of the IoT require Big Data systems that can handle ingest, transactions and analytics concurrently adapting to varied situations as they occur, with speed at scale. In his session at @ThingsExpo, Chad Jones, chief strategy officer at Deep Information Sciences, will look differently at IoT data so enterprises can fully leverage their IoT potential. He’ll sha...
The modern software development landscape consists of best practices and tools that allow teams to deliver software in a near-continuous manner. By adopting a culture of automation, measurement and sharing, the time to ship code has been greatly reduced, allowing for shorter release cycles and quicker feedback from customers and users. Still, with all of these tools and methods, how can teams stay on top of what is taking place across their infrastructure and codebase? Hopping between services a...
In today's digital world, change is the one constant. Disruptive innovations like cloud, mobility, social media, and the Internet of Things have reshaped the market and set new standards in customer expectations. To remain competitive, businesses must tap the potential of emerging technologies and markets through the rapid release of new products and services. However, the rigid and siloed structures of traditional IT platforms and processes are slowing them down – resulting in lengthy delivery ...
As a CIO, are your direct reports IT managers or are they IT leaders? The hard truth is that many IT managers have risen through the ranks based on their technical skills, not their leadership ability. Many are unable to effectively engage and inspire, creating forward momentum in the direction of desired change. Renowned for its approach to leadership and emphasis on their people, organizations increasingly look to our military for insight into these challenges.
Overgrown applications have given way to modular applications, driven by the need to break larger problems into smaller problems. Similarly large monolithic development processes have been forced to be broken into smaller agile development cycles. Looking at trends in software development, microservices architectures meet the same demands. Additional benefits of microservices architectures are compartmentalization and a limited impact of service failure versus a complete software malfunction....
Containers are changing the security landscape for software development and deployment. As with any security solutions, security approaches that work for developers, operations personnel and security professionals is a requirement. In his session at @DevOpsSummit, Kevin Gilpin, CTO and Co-Founder of Conjur, will discuss various security considerations for container-based infrastructure and related DevOps workflows.
DevOps and Continuous Delivery software provider XebiaLabs has announced it has been selected to join the Amazon Web Services (AWS) DevOps Competency partner program. The program is designed to highlight software vendors like XebiaLabs who have demonstrated technical expertise and proven customer success in DevOps and specialized solution areas like Continuous Delivery. DevOps Competency Partners provide solutions to, or have deep experience working with AWS users and other businesses to help t...
Nowadays, a large number of sensors and devices are connected to the network. Leading-edge IoT technologies integrate various types of sensor data to create a new value for several business decision scenarios. The transparent cloud is a model of a new IoT emergence service platform. Many service providers store and access various types of sensor data in order to create and find out new business values by integrating such data.
The cloud has reached mainstream IT. Those 18.7 million data centers out there (server closets to corporate data centers to colocation deployments) are moving to the cloud. In his session at 17th Cloud Expo, Achim Weiss, CEO & co-founder of ProfitBricks, will share how two companies – one in the U.S. and one in Germany – are achieving their goals with cloud infrastructure. More than a case study, he will share the details of how they prioritized their cloud computing infrastructure deployments ...
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, will show 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 will get the download information, scripts, and complete en...
Data loss happens, even in the cloud. In fact, if your company has adopted a cloud application in the past three years, data loss has probably happened, whether you know it or not. In his session at 17th Cloud Expo, Bryan Forrester, Senior Vice President of Sales at eFolder, will present how common and costly cloud application data loss is and what measures you can take to protect your organization from data loss.