JDOM：优化Java的XML处理工具

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JDOM（Java Document Object Model）是Java领域的一种开源库，专为优化XML数据操作而设计。与W3C（World Wide Web Consortium）的标准文档对象模型（DOM）不同，JDOM并非基于DOM或模仿其架构，而是作为Java特定的解决方案出现。它的核心优势在于利用Java语言的特性，如方法重载、集合框架、反射以及熟悉的编程模式，使得在Java环境中处理XML变得更为直观和高效。相比于DOM，JDOM的主要特点包括： 1. **语言专一性**：JDOM是为Java编写的，它充分利用了Java语言的优势，使得代码更加简洁和高效。例如，通过Java的类继承和多态性，JDOM提供了更丰富的操作手段，这在处理XML文档时尤其显著。 2. **方法重载**：JDOM支持方法重载，允许开发者根据需求定义多个具有相同名称但参数列表不同的方法，这对于XML文档的遍历和节点操作非常有用。 3. **集合框架**：由于XML本质上是一种树状结构，JDOM将XML文档映射为Java的集合，如List和Map，使得开发者可以方便地对节点进行批量操作，提高了代码的可读性和性能。 4. **反射机制**：JDOM支持反射，允许动态访问和修改XML节点的属性和内容，增强了程序的灵活性和扩展性。 5. **熟悉编程范式**：对于熟悉Java编程的开发者而言，JDOM的API设计遵循了Java的惯用语法和编程逻辑，使得上手更容易，开发效率更高。 6. **开源与商业友好**：JDOM可以在www.jdom.org找到，并采用Apache风格的开放源代码许可证，这意味着用户可以根据项目需求自由使用和修改代码，同时考虑到商业项目的兼容性。 JDOM为Java开发者提供了一种更贴近语言特性的XML处理工具，简化了XML文档的操作，提高了开发效率，是构建Java应用程序处理XML数据的强大工具。

JDOM and XML Parsing, Part 1

JDOM makes XML manipulation in Java easier than ever.

hances are, you’ve probably used one of a

number of Java libraries to manipulate

XML data structures in the past. So what’s

the point of JDOM (Java Document Object

Model), and why do developers need it?

JDOM is an open source library for

Java-optimized XML data manipulations. Although it’s

similar to the World Wide Web Consortium’s (W3C)

DOM, it’s an alternative document object model that

was not built on DOM or modeled after DOM. The

main difference is that while DOM was created to be

language-neutral and initially used for JavaScript

manipulation of HTML pages, JDOM was created to be

Java-specific and thereby take advantage of Java’s

features, including method overloading, collections,

reflection, and familiar programming idioms. For Java

programmers, JDOM tends to feel more natural and

“right.” It’s similar to how the Java-optimized remote

method invocation library feels more natural than the

language-neutral Common Object Request Broker

Architecture.

You can find JDOM at www.jdom.org under an open

source Apache-style (commercial-friendly) license. It’s

collaboratively designed and developed and has mailing

lists with more than 3,000 subscribers. The library has

also been accepted by Sun’s Java Community Process

(JCP) as a Java Specification Request (JSR-102) and is

on track to become a formal Java specification.

The articles in this series will provide a technical

introduction to JDOM. This article provides information

about important classes. The next article will give you a

feel for how to use JDOM inside your own Java programs.

THE JDOM PACKAGE STRUCTURE

The JDOM library consists of six packages. First, the

org.jdom package holds the classes representing an

XML document and its components:

Attribute,

CDATA, Comment, DocType, Document, Element, EntityRef,

Namespace, ProcessingInstruction, and Text. If you’re

familiar with XML, the class names should be self-

explanatory.

Next is the

org.jdom.input package. which holds

classes that build XML documents. The main and most

important class is

SAXBuilder. SAXBuilder builds a

document by listening to incoming SAX events and

constructing a corresponding document. When you want

to build from a file or other stream, you use

SAXBuilder.

It uses a SAX parser to read the stream and then builds

the document according to the SAX parser callbacks. The

good part of this design is that as SAX parsers get faster,

SAXBuilder gets faster. The other main input class is

DOMBuilder. DOMBuilder builds from a DOM tree. This

class comes in handy when you have a preexisting DOM

tree and want a JDOM version instead.

There’s no limit to the potential builders. For example,

now that Xerces has the Xerces Native Interface (XNI) to

operate at a lower level than SAX, it may make sense to

write an

XNIBuilder to support some parser knowledge

not exposed via SAX. One popular builder that has been

contributed to the project is the

ResultSetBuilder. It

takes a JDBC result set and creates an XML document

representation of the SQL result, with various

configurations regarding what should be an element and

what should be an attribute.

The

org.jdom.output package holds the classes that

output XML documents. The most important class is

XMLOutputter. It converts documents to a stream of

bytes for output to files, streams, and sockets. The

XMLOutputter has many special configuration options

supporting raw output, pretty output, or compressed

output, among others. It’s a fairly complicated class.

That’s probably why this capability still doesn’t exist

in DOM Level 2.

Other outputters include the

SAXOutputter, which

generates SAX events based on the document content.

Although seemingly arcane, this class proves extremely

useful in XSLT transforms, because SAX events can be a

more efficient way than bytes to transfer document data

to an engine. There’s also a

DOMOutputter, which builds a

DOM tree representation of the document. An

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