|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).
“The Internet of Things transforms the way organizations leverage machine data and gain insights from it,” noted Splunk’s CTO Snehal Antani, as Splunk announced accelerated momentum in Industrial Data and the IoT. The trend is driven by Splunk’s continued investment in its products and partner ecosystem as well as the creativity of customers and the flexibility to deploy Splunk IoT solutions as software, cloud services or in a hybrid environment. Customers are using Splunk® solutions to collect and correlate data from control systems, sensors, mobile devices and IT systems for a variety of Ind...
Oct. 4, 2015 04:45 PM EDT Reads: 551
As enterprises capture more and more data of all types – structured, semi-structured, and unstructured – data discovery requirements for business intelligence (BI), Big Data, and predictive analytics initiatives grow more complex. A company’s ability to become data-driven and compete on analytics depends on the speed with which it can provision their analytics applications with all relevant information. The task of finding data has traditionally resided with IT, but now organizations increasingly turn towards data source discovery tools to find the right data, in context, for business users, d...
Oct. 4, 2015 04:00 PM EDT Reads: 354
Clearly the way forward is to move to cloud be it bare metal, VMs or containers. One aspect of the current public clouds that is slowing this cloud migration is cloud lock-in. Every cloud vendor is trying to make it very difficult to move out once a customer has chosen their cloud. In his session at 17th Cloud Expo, Naveen Nimmu, CEO of Clouber, Inc., will advocate that making the inter-cloud migration as simple as changing airlines would help the entire industry to quickly adopt the cloud without worrying about any lock-in fears. In fact by having standard APIs for IaaS would help PaaS expl...
Oct. 4, 2015 02:30 PM EDT Reads: 370
Organizations already struggle with the simple collection of data resulting from the proliferation of IoT, lacking the right infrastructure to manage it. They can't only rely on the cloud to collect and utilize this data because many applications still require dedicated infrastructure for security, redundancy, performance, etc. In his session at 17th Cloud Expo, Emil Sayegh, CEO of Codero Hosting, will discuss how in order to resolve the inherent issues, companies need to combine dedicated and cloud solutions through hybrid hosting – a sustainable solution for the data required to manage I...
Oct. 4, 2015 02:00 PM EDT Reads: 387
SYS-CON Events announced today that ProfitBricks, the provider of painless cloud infrastructure, will exhibit at SYS-CON's 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. ProfitBricks is the IaaS provider that offers a painless cloud experience for all IT users, with no learning curve. ProfitBricks boasts flexible cloud servers and networking, an integrated Data Center Designer tool for visual control over the cloud and the best price/performance value available. ProfitBricks was named one of the coolest Clo...
Oct. 4, 2015 01:00 PM EDT Reads: 693
SYS-CON Events announced today that IBM Cloud Data Services has been named “Bronze Sponsor” of SYS-CON's 17th Cloud Expo, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. IBM Cloud Data Services offers a portfolio of integrated, best-of-breed cloud data services for developers focused on mobile computing and analytics use cases.
Oct. 4, 2015 01:00 PM EDT Reads: 532
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 Thingies, will discuss and demonstrate how devices and humans can be integrated from a simple clust...
Oct. 4, 2015 12:00 PM EDT Reads: 602
Apps and devices shouldn't stop working when there's limited or no network connectivity. Learn how to bring data stored in a cloud database to the edge of the network (and back again) whenever an Internet connection is available. In his session at 17th Cloud Expo, Bradley Holt, Developer Advocate at IBM Cloud Data Services, will demonstrate techniques for replicating cloud databases with devices in order to build offline-first mobile or Internet of Things (IoT) apps that can provide a better, faster user experience, both offline and online. The focus of this talk will be on IBM Cloudant, Apa...
Oct. 4, 2015 11:00 AM EDT Reads: 343
As more and more data is generated from a variety of connected devices, the need to get insights from this data and predict future behavior and trends is increasingly essential for businesses. Real-time stream processing is needed in a variety of different industries such as Manufacturing, Oil and Gas, Automobile, Finance, Online Retail, Smart Grids, and Healthcare. Azure Stream Analytics is a fully managed distributed stream computation service that provides low latency, scalable processing of streaming data in the cloud with an enterprise grade SLA. It features built-in integration with Azur...
Oct. 4, 2015 11:00 AM EDT Reads: 707
You have your devices and your data, but what about the rest of your Internet of Things story? Two popular classes of technologies that nicely handle the Big Data analytics for Internet of Things are Apache Hadoop and NoSQL. Hadoop is designed for parallelizing analytical work across many servers and is ideal for the massive data volumes you create with IoT devices. NoSQL databases such as Apache HBase are ideal for storing and retrieving IoT data as “time series data.”
Oct. 4, 2015 10:45 AM EDT Reads: 353
SYS-CON Events announced today that HPM Networks will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. For 20 years, HPM Networks has been integrating technology solutions that solve complex business challenges. HPM Networks has designed solutions for both SMB and enterprise customers throughout the San Francisco Bay Area.
Oct. 4, 2015 09:00 AM EDT Reads: 542
Mobile messaging has been a popular communication channel for more than 20 years. Finnish engineer Matti Makkonen invented the idea for SMS (Short Message Service) in 1984, making his vision a reality on December 3, 1992 by sending the first message ("Happy Christmas") from a PC to a cell phone. Since then, the technology has evolved immensely, from both a technology standpoint, and in our everyday uses for it. Originally used for person-to-person (P2P) communication, i.e., Sally sends a text message to Betty – mobile messaging now offers tremendous value to businesses for customer and empl...
Oct. 4, 2015 08:30 AM EDT Reads: 150
SYS-CON Events announced today that MobiDev, a software development company, will exhibit at the 17th International Cloud Expo®, which will take place November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. MobiDev is a software development company with representative offices in Atlanta (US), Sheffield (UK) and Würzburg (Germany); and development centers in Ukraine. Since 2009 it has grown from a small group of passionate engineers and business managers to a full-scale mobile software company with over 150 developers, designers, quality assurance engineers, project manage...
Oct. 4, 2015 04:00 AM EDT Reads: 659
The broad selection of hardware, the rapid evolution of operating systems and the time-to-market for mobile apps has been so rapid that new challenges for developers and engineers arise every day. Security, testing, hosting, and other metrics have to be considered through the process. In his session at Big Data Expo, Walter Maguire, Chief Field Technologist, HP Big Data Group, at Hewlett-Packard, will discuss the challenges faced by developers and a composite Big Data applications builder, focusing on how to help solve the problems that developers are continuously battling.
Oct. 4, 2015 04:00 AM EDT Reads: 322
SYS-CON Events announced today that Cloud Raxak has been named “Media & Session Sponsor” of SYS-CON's 17th Cloud Expo, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Raxak Protect automates security compliance across private and public clouds. Using the SaaS tool or managed service, developers can deploy cloud apps quickly, cost-effectively, and without error.
Oct. 3, 2015 01:15 PM EDT Reads: 572
Who are you? How do you introduce yourself? Do you use a name, or do you greet a friend by the last four digits of his social security number? Assuming you don’t, why are we content to associate our identity with 10 random digits assigned by our phone company? Identity is an issue that affects everyone, but as individuals we don’t spend a lot of time thinking about it. In his session at @ThingsExpo, Ben Klang, Founder & President of Mojo Lingo, will discuss the impact of technology on identity. Should we federate, or not? How should identity be secured? Who owns the identity? How is identity ...
Oct. 3, 2015 11:00 AM EDT Reads: 396
SYS-CON Events announced today that Solgeniakhela will exhibit at SYS-CON's 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Solgeniakhela is the global market leader in Cloud Collaboration and Cloud Infrastructure software solutions. Designed to “Bridge the Gap” between Personal and Professional Social, Mobile and Cloud user experiences, our solutions help large and medium-sized organizations dramatically improve productivity, reduce collaboration costs, and increase the overall enterprise value by bringing ...
Oct. 2, 2015 10:00 PM EDT Reads: 539
Sensors and effectors of IoT are solving problems in new ways, but small businesses have been slow to join the quantified world. They’ll need information from IoT using applications as varied as the businesses themselves. In his session at @ThingsExpo, Roger Meike, Distinguished Engineer, Director of Technology Innovation at Intuit, will show how IoT manufacturers can use open standards, public APIs and custom apps to enable the Quantified Small Business. He will use a Raspberry Pi to connect sensors to web services, and cloud integration to connect accounting and data, providing a Bluetooth...
Oct. 2, 2015 03:30 PM EDT Reads: 337
SYS-CON Events announced today that Micron Technology, Inc., a global leader in advanced semiconductor systems, will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Micron’s broad portfolio of high-performance memory technologies – including DRAM, NAND and NOR Flash – is the basis for solid state drives, modules, multichip packages and other system solutions. Backed by more than 35 years of technology leadership, Micron's memory solutions enable the world's most innovative computing, consumer,...
Oct. 2, 2015 07:00 AM EDT Reads: 553
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.
Oct. 1, 2015 02:30 PM EDT Reads: 395