Introduction to Server-Side XML

Server Used for Examples

For the examples in this chapter, we used Apache 1.3.26 and PHP 4.2.2 on Windows 2000 Professional.

JSP

JavaServer Pages (JSP)are written in Java, which (unlike VBScript and PHP) is an object-oriented programming language that can be used to build enterprise-strength applications. Java is arguably the most powerful platform for server-side web development today. Portability, multithreading, extensive class libraries, object-oriented code, strong safety features, robust security measures, elegance, and extensibility are just a few of Java's advantages.

Java was designed to be platform-independent and very portable. Therefore, a web application developed in Java can be packaged as a WAR (web application archive) file and installed on any Java-enabled application server, on any platform.

The disadvantage is that Java is not very easy to learn. If you just need to get a more simple site up and working quickly, and are not serious about learning an object-oriented language, a simpler language like PHP might be a better choice. By using JavaBeans and tag libraries, however, web designers can quickly learn to create JSPs that retrieve data from a database, process XML, and carry out other powerful functions, without having to know anything about the underlying technology. You don't need to be a sophisticated Java programmer to utilize the power of JSP.

JSP files can also be a little slower than ASP or PHP because of the way they work. The first time JSPs are called, they are converted into servlets (special Java classes that produce outputs for sending over HTTP), which are stored by the JSP engine. After this, requests for the JSP files are served from the converted servlet (JSP engines also double as servlet engines). The most readily available JSP engine is Tomcat, which also serves static content at a slower rate. If you want a fast web site, get a dedicated web server such as Apache or IIS to serve the static content, while Tomcat (or another engine) serves the JSP content.

Advantages

·          It's free. You can download the Tomcat application server from the Jakarta web site, and start coding in minutes (assuming you've got Java installed, which is also free).

·          It's cross-platform.

·          It has a very active user community.

·          It's extremely powerful and scalable.

Drawbacks

·          A steep learning curve.

·          Third-party hosting isn't common, and can cost extra for installation.

XML Support

There is enormous XML support in Java. There are loads of parsers and XSLT and XPath processors available, and most of them are open source. To name them all would be pointless, but the following is a short overview of some of the products available (the list includes the most popular products in each category).

XML Parsers

·          Xerces: Xerces is a high-performance, fully compliant XML parser from the Apache XML Project. It is a fully conforming XML Schema processor. It is free, and available both in sourcecode and precompiled binary (JAR file) form. For more information, visit http://xml.apache.org/xerces2-j/index.html.

·          XML4J: XML Parser for Java is a validating XML parser and processor written in 100% pure Java  a library for parsing and generating XML documents, available as freeware from IBM. For more information, visit http://www.alphaworks.ibm.com/tech/xml4j.

·          XP: XP is an XML 1.0 parser written in Java, fully conforming, which detects all non well-formed documents. It is currently not a validating XSLT processor, but it can parse all external entities: external DTD subsets, external parameter entities, and external general entities. For more information, visit http://www.jclark.com/xml/xp/.

·          MXP1: MXPl, or Maximum Perf. Minimum Size XML Parser, is a Java-based, non-validating pull parser that implements the Common Application Programming Interface (API) for XML Pull Parsing (http://www.xmlpull.org) specification. MXP1 was designed for minimal footprint (less than 20k) and maximum speed (it claims up to 20% better performance than the nearest competitor) and is suited for fast serialization and deserialization of Simple Object Access Protocol (SOAP)-based XML objects. For more information, visit http://www.extreme.indiana.edu/xgws/xsoap/xpp/mxp1/.

XSLT Processors

·          Xalan: Xalan is an XSLT processor for transforming XML documents, from the Apache XML Project. It implements the W3C Recommendations for XSL Transformations (XSLT) and the XML Path Language (XPath). It can be used from the command line, in an applet or a servlet, or as a module in other programs. For more information, visit http://xml.apache.org/xalan-j/index.html.

·          XT: XT is a fast, free implementation of XSLT in Java. For more information, visit http://www.blnz.com/xt/index.html.

·          SAXON: The SAXON package is a collection of tools for processing XML documents. It contains an XSLT processor, and Java libraries for access to the processor from Java applications. For more information, visit http://saxon.sourceforge.net/.

Java-Specific Document Object Models

These are frameworks that provide a more Java-centric coding approach to parsing, transforming, etc. than the DOM and SAX interfaces. They can be configured to use DOM or SAX for parsing, but provide a much more convenient API for Java programs.

·          JDOM: JDOM is, quite simply, a Java representation of an XML document. JDOM provides a way to represent that document for easy and efficient reading, manipulation, and writing. It has a straightforward API, is lightweight, fast, and is optimized for the Java programmer. It's an alternative to DOM and SAX, although it integrates well with both of them. For more information, visit http://www.jdom.org.

·          dom4j: dom4j is an easy to use, open source library for working with XML, XPath, and XSLT on the Java platform using the Java Collections Framework and with full support for DOM, SAX, JAXP, TrAX, and XSLT. dom4j is distributed under an open source, Apache-style license that does not restrict users to creation of open source products only. For more information, visit http://www.dom4j.org.

Other

·          Java XML Pack: The Java XML Pack is an all-in-one download of Java technologies for XML from SUN. Java XML Pack brings together several of the key industry standards for XML  such as SAX, DOM, XSLT, SOAP, UDDI, ebXML, and WSDL  into one convenient download, thereby giving developers the technologies needed to get started with web applications and Web Services. Included in the bundle are: Java API for XML Processing (JAXP), Java Architecture for XML Binding (JAXB), Java API for XML Messaging (JAXM), Java API for XML-based RPC (JAX-RPC), and Java API for XML Registries (JAXR). For more information, visit http://java.sun.com/xml/javaxmlpack.html.

·          Cocoon: Cocoon is an XML framework that allows easy integrated usage of XML and XSLT technologies for server applications, around pipelined SAX processing, with a centralized configuration system to make things simple. It is available for usage under the Apache Software License. For more information, visit http://xml.apache.org/cocoon/index.html.

There are also lots of utility packages available, such as XML tag libraries (XTags) for JSP from Jakarta, which give web designers with limited Java knowledge the full powers of XML processing through simple tags. For more information, visit http://jakarta.apache.org/taglibs/doc/xtags-doc/intro.html.