|By Shari Jones||
|August 17, 2001 12:00 AM EDT||
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.
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(" ",
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 java.io.OutputStream as well as to a java.io.Writer, 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 HelloWorld.java file, type the following code:
After the HelloWorld.java file compiles, run the HelloWorld application using:
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 HelloWorld.java file, specifically from the line that instantiates a new Element. Here is the code that defines the name of the new Element.
The text "Hello World!" also was defined in the code in the HelloWorld.java 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 java.io.File, java.io.InputStream, java.io.Reader, a URI specified as a java.lang.String, or a java.net.URL.
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 DOMBuilder.build methods to build a JDOM document from an existing DOM document object. This build method is just like the SAXBuilder.build 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 DOMBuilder.build methods, each of these taking a single argument - either a java.io.File, java.io.InputStream, or a java.net.URL - 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 SAXBuilder.build 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 =
.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: www.jdom.org
2. JDOM discussion lists: www.jdom.org/involved/lists.html
3. Java API for XML Processing (JAXP): http://java.sun.com/xml/xml_jaxp.html
4. The Collections API for JDK 1.1: www.java.sun.com/products/javabeans/infobus/
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 (www-106.ibm.com/developerworks/xml/library/x-tipjdom.html).
Technology is enabling a new approach to collecting and using data. This approach, commonly referred to as the "Internet of Things" (IoT), enables businesses to use real-time data from all sorts of things including machines, devices and sensors to make better decisions, improve customer service, and lower the risk in the creation of new revenue opportunities. In his General Session at Internet of @ThingsExpo, Dave Wagstaff, Vice President and Chief Architect at BSQUARE Corporation, discuss the ...
Feb. 1, 2015 03:45 PM EST Reads: 3,180
“We help people build clusters, in the classical sense of the cluster. We help people put a full stack on top of every single one of those machines. We do the full bare metal install," explained Greg Bruno, Vice President of Engineering and co-founder of StackIQ, in this SYS-CON.tv interview at 15th Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Feb. 1, 2015 02:45 PM EST Reads: 2,647
At 15th Cloud Expo, Shrikant Pattathil, Executive Vice President at Harbinger Systems, demos a video delivery platform that helps you do interactive videos. He discusses how Harbinger is accomplishing it in the cloud world, the problems they faced and the choices they made to get around these problems.
Feb. 1, 2015 02:45 PM EST Reads: 1,778
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Feb. 1, 2015 02:30 PM EST Reads: 2,802
CloudBees, Inc., has announced a $23.5 million financing round, led by longtime CloudBees investor Lightspeed Venture Partners. Existing investors Matrix Partners, Verizon Ventures and Blue Cloud Ventures also participated in the round. The latest funding announcement follows earlier rounds of $4 million, $10.5 million and $10.8 million, bringing the total investment in CloudBees to just under $50 million since the company’s inception in 2010. Previous venture investment rounds were led by Ma...
Feb. 1, 2015 02:00 PM EST Reads: 1,077
In this Women in Technology Power Panel at 15th Cloud Expo, moderated by Anne Plese, Senior Consultant, Cloud Product Marketing at Verizon Enterprise, Esmeralda Swartz, CMO at MetraTech; Evelyn de Souza, Data Privacy and Compliance Strategy Leader at Cisco Systems; Seema Jethani, Director of Product Management at Basho Technologies; Victoria Livschitz, CEO of Qubell Inc.; Anne Hungate, Senior Director of Software Quality at DIRECTV, discussed what path they took to find their spot within the tec...
Feb. 1, 2015 01:45 PM EST Reads: 2,474
The cloud is becoming the de-facto way for enterprises to leverage common infrastructure while innovating and one of the biggest obstacles facing public cloud computing is security. In his session at 15th Cloud Expo, Jeff Aliber, a global marketing executive at Verizon, discussed how the best place for web security is in the cloud. Benefits include: Functions as the first layer of defense Easy operation –CNAME change Implement an integrated solution Best architecture for addressing network-l...
Feb. 1, 2015 01:30 PM EST Reads: 2,384
DevOps Summit 2015 New York, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that it is now accepting Keynote Proposals. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long development cycles that produce software that is obsolete...
Feb. 1, 2015 01:15 PM EST Reads: 2,802
The 3rd International Internet of @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that its Call for Papers is now open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
Feb. 1, 2015 01:15 PM EST Reads: 3,278
“DevOps is really about the business. The business is under pressure today, competitively in the marketplace to respond to the expectations of the customer. The business is driving IT and the problem is that IT isn't responding fast enough," explained Mark Levy, Senior Product Marketing Manager at Serena Software, in this SYS-CON.tv interview at DevOps Summit, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Feb. 1, 2015 01:00 PM EST Reads: 2,730
Today, IT is not just a cost center. IT is an enabler and driver of business. With the emergence of the hybrid cloud paradigm, IT now has increasingly more capabilities to create new strategic opportunities for a business. Hybrid cloud allows an organization to utilize multi-tenant public clouds, dedicated private clouds, bare metal hosting, and the associated support and services for the right use cases through an on-demand, XaaS model. This model of IT creates tremendous opportunities for busi...
Feb. 1, 2015 01:00 PM EST Reads: 1,712
Cloud computing started a technology revolution; now DevOps is driving that revolution forward. By enabling new approaches to service delivery, cloud and DevOps together are delivering even greater speed, agility, and efficiency. No wonder leading innovators are adopting DevOps and cloud together! In his session at DevOps Summit, Andi Mann, Vice President of Strategic Solutions at CA Technologies, explored the synergies in these two approaches, with practical tips, techniques, research data, wa...
Feb. 1, 2015 01:00 PM EST Reads: 3,313
Software AG and Wipro Ltd. have announced a joint solution platform for streaming analytics that provides real-time actionable intelligence for the Internet of Things (IoT) market. “The key to successfully addressing the IoT market is the ability to rapidly build and evolve apps that tap into, analyze and make smart decisions on fast, big data”, said John Bates, Global Head of Industry Solutions and CMO, Software AG. To address the huge market potential created by streaming analytics in conj...
Feb. 1, 2015 01:00 PM EST Reads: 1,216
Appcore deploys cloud for service providers based on the Apache Cloud set. In this demo at 15th Cloud Expo, Nate Gordon, Director of Technology at Appcore, shows their new product that's coming out in January - Appcore Atlas, which is focused on deploying private clouds based on CloudStack in 15 minutes or less. Our upcoming June 9-11, 2015, event in New York City will present a total of 10 simultaneous tracks (the largest conference content in the world) by an all-star faculty, over three days...
Feb. 1, 2015 01:00 PM EST Reads: 1,646
Amazon, Google and Facebook are household names in part because of their mastery of Big Data. But what about organizations without billions of dollars to spend on Big Data tools - how can they extract value from their data? In his session at 6th Big Data Expo®, Ali Ghodsi, Co-Founder and Head of Engineering at Databricks, discussed how the zero management cost and scalability of the cloud is addressing the challenges and pain points that data engineers face when working with Big Data. He also s...
Feb. 1, 2015 01:00 PM EST Reads: 2,582
The Industrial Internet revolution is now underway, enabled by connected machines and billions of devices that communicate and collaborate. The massive amounts of Big Data requiring real-time analysis is flooding legacy IT systems and giving way to cloud environments that can handle the unpredictable workloads. Yet many barriers remain until we can fully realize the opportunities and benefits from the convergence of machines and devices with Big Data and the cloud, including interoperability, ...
Feb. 1, 2015 01:00 PM EST Reads: 3,045
IBM has announced a new strategic technology services agreement with Anthem, Inc., a health benefits company in the U.S. IBM has been selected to provide operational services for Anthem's mainframe and data center server and storage infrastructure for the next five years. Among the benefits of the relationship, Anthem has the ability to leverage IBM Cloud solutions that will help increase the ease, availability and speed of adding infrastructure to support new business requirements.
Feb. 1, 2015 01:00 PM EST Reads: 1,623
The term culture has had a polarizing effect among DevOps supporters. Some propose that culture change is critical for success with DevOps, but are remiss to define culture. Some talk about a DevOps culture but then reference activities that could lead to culture change and there are those that talk about culture change as a set of behaviors that need to be adopted by those in IT. There is no question that businesses successful in adopting a DevOps mindset have seen departmental culture change, ...
Feb. 1, 2015 12:45 PM EST Reads: 2,699
CA Technologies released a new study – “DevOps: The Worst-Kept Secret to Winning in the Application Economy” – that reveals that 82% of enterprises in Asia Pacific and Japan (APJ) already have or plan to adopt a DevOps strategy, a 12 point increase from last year’s figure of 70%. DevOps is a methodology which helps foster collaboration between the teams that create and test applications (Dev) with those that maintain them in production environments (Ops). Vanson Bourne conducted the survey with...
Feb. 1, 2015 12:30 PM EST Reads: 893
Connected devices and the Internet of Things are getting significant momentum in 2014. In his session at Internet of @ThingsExpo, Jim Hunter, Chief Scientist & Technology Evangelist at Greenwave Systems, examined three key elements that together will drive mass adoption of the IoT before the end of 2015. The first element is the recent advent of robust open source protocols (like AllJoyn and WebRTC) that facilitate M2M communication. The second is broad availability of flexible, cost-effective ...
Feb. 1, 2015 12:00 PM EST Reads: 2,936