3.3 JAXP: Java API for XML Processing

1. 3.3 JAXP: Java API for XML Processing • How can applications use XML processors? • A Java-based answer: through JAXP • An overview of the JAXP interface • What does it specify? • What can be done with it? • How do the JAXP components fit together? [Partly based on tutorial “An Overview of the APIs” available at http://java.sun.com/xml/jaxp/dist/1.1/docs/tutorial/overview/3_apis.html, from which also some graphics are borrowed] Notes 3: XML Processor Interfaces

2. JAXP 1.1 • An interface for “plugging-in” and using XML processors in Java applications • includes packages • org.xml.sax: SAX 2.0 interface • org.w3c.dom: DOM Level 2 interface • javax.xml.parsers: initialization and use of parsers • javax.xml.transform: initialization and use of transformers (XSLT processors) • Included in JDK starting from vers. 1.4 Notes 3: XML Processor Interfaces

3. JAXP: XML processor plugin (1) • Vendor-independent method for selecting processor implementation at run time • principally through system propertiesjavax.xml.parsers.SAXParserFactory,javax.xml.parsers.DocumentBuilderFactory, andjavax.xml.transform.TransformerFactory • For example:System.setProperty("javax.xml.parsers.DocumentBuilderFactory", "com.icl.saxon.om.DocumentBuilderFactoryImpl"); Notes 3: XML Processor Interfaces

4. JAXP: XML processor plugin (2) • By default, reference implementations used • Apache Crimson/Xerces as the XML parser • Apache Xalan as the XSLT processor • Currently supported only by a few compliant XML processors: • Parsers: Apache Crimson and Xerces, Aelfred • XSLT transformers: Apache Xalan, Saxon Notes 3: XML Processor Interfaces

5. JAXP: Functionality • Parsing using SAX 2.0 or DOM Level 2 • Transformation using XSLT • (We’ll perform stand-alone transformations later) • Fixes features left unspecified in SAX 2.0 and DOM Level 2 • control of parser validation and error handling • creation and saving of DOM Document objects Notes 3: XML Processor Interfaces

6. JAXP Parsing API • Included in JAXP package javax.xml.parsers • Used for invoking and using SAX and DOM parser implementations:SAXParserFactory spf =SAXParserFactory.newInstance();DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); Notes 3: XML Processor Interfaces

7. getXMLReader XML JAXP: Using an SAX parser (1) Notes 3: XML Processor Interfaces

8. JAXP: Using an SAX parser (2) • We’ve already used this: SAXParserFactory spf =SAXParserFactory.newInstance(); try { SAXParser saxParser = spf.newSAXParser(); XMLReader xmlReader = saxParser.getXMLReader(); } catch (Exception e) { System.err.println(e.getMessage()); System.exit(1); }; Notes 3: XML Processor Interfaces

9. parse( ”f.xml”) newDocument() f.xml JAXP: Using a DOM parser (1) Notes 3: XML Processor Interfaces

10. JAXP: Using a DOM parser (2) • We’ve used this, too: DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); try {// to get a newDocumentBuilder:documentBuilder builder = dbf.newDocumentBuilder(); } catch (ParserConfigurationException e) { e.printStackTrace()); System.exit(1); }; Notes 3: XML Processor Interfaces

11. XML DOM building in JAXP Document Builder (Content Handler) XML Reader Error Handler DOM Document (SAX Parser) DTD Handler Entity Resolver DOM on top of SAX - So what? Notes 3: XML Processor Interfaces

12. Validation and namespace processing can be controlled, both for SAXParserFactories and DocumentBuilderFactories with setValidating(boolean)and setNamespaceAware(boolean) JAXP: Controlling parsing • Errors of DOM parsing can be handled • by creating a SAXErrorHandler, which implements error, fatalError and warning methods, and passing it with setErrorHandler to the DocumentBuilder Notes 3: XML Processor Interfaces

13. JAXP Transformation API • also known as TrAX • Allows application to apply a Transformer to a Source document to get a Result document • Transformer can be created • from XSLT transformation instructions (to be discussed later) • without instructions, which gives an identity transformation (simply copies Source to Result) Notes 3: XML Processor Interfaces

14. JAXP: Using Transformers (1) XSLT Notes 3: XML Processor Interfaces

15. JAXP Transformation Packages • javax.xml.transform: • Classes Transformer and TransformerFactory; initialization similar to parsers and parser factories • Transformation Source object can be • a DOM tree, an SAX XMLReader or an I/O stream • Transformation Result object can be • a DOM tree, an SAX ContentHandler or an I/O stream Notes 3: XML Processor Interfaces

16. JAXP Transformation Packages (2) • Classes to create Source and Result objects from DOM, SAX and I/O streams defined in packages • javax.xml.transform.dom,javax.xml.transform.sax,andjavax.xml.transform.stream • An identity transformation from a DOM Document to I/O stream a vendor-neutral way to serialize DOM documents • (the only option in JAXP) Notes 3: XML Processor Interfaces

17. Serializing a DOM Document as XML text • Identity transformation to an I/O stream Result: TransformerFactory tFactory =TransformerFactory.newInstance(); // Create an identity transformer:Transformer transformer = tFactory.newTransformer();DOMSource source = new DOMSource(myDOMdoc);StreamResult result = new StreamResult(System.out);transformer.transform(source, result); Notes 3: XML Processor Interfaces

18. Other Java APIs for XML • JDOM • variant of W3C DOM; closer to Java object-orientation (http://www.jdom.org/) • DOM4J (http://www.dom4j.org/) • roughly similar to JDOM; richer set of features • JAXB (Java Architecture for XML Binding) • compiles DTDs to DTD-specific classes that allow to read, to manipulate and to write valid documents • http://java.sun.com/xml/jaxb/ Notes 3: XML Processor Interfaces

19. JAXP: Summary • An interface for using XML Processors • SAX/DOM parsers, XSLT transformers • Supports plugability of different implementations • Defines means to control validation, and handling of parse errors (through SAX ErrorHandlers) • Defines means to write out DOM Documents • Included in JDK 1.4 Notes 3: XML Processor Interfaces