JAX- Java APIs for XML

by J. Pearce

Some XML Standards• Basic

– SAX (sequential access parser)

– DOM (random access parser)

– XSL (XSLT, XPATH)

– DTD

• Schema

• Linking & Presentation

– XPATH, XLINK, XBASE, XHTML

• Semantic Web– RDF (Resource Description Framework)

– OWL (Ontology Web Language)

– XTP (XML Topic Maps)

JAX Supports Java Web Services

• Java Web Service is a B2B service implemented in Java

• Web clients, apps, and services communicate and share data using XML

• JAX is a layer of APIs that sits on top of J2EE

JAX Consists of

• Document-oriented– JAXP (JAX Processing)

• Procedure-oriented– JAX-RPC (SOAP method calls)– JAX-M (SOAP messages)– JAX-R (business registries)

Major JAX packages

• javax.xml.soap

• javax.xml.transform

• javax.xml.rpc

• javax.xml.messaging

• javax.xml.namespace

• javax.xml.parsers

• org.w3c.dom

• org.xml.sax

JAXP Includes:

• javax.xml.parsers– SAX API– DOM API

• javax.xml.transform– XSLT API

• javax.xml.namespace

Parsers

• SAX is an event-notification parser

• DOM is a tree-building parser

SAX

SAXParserparse()

DefaultHandler

XMLReader<<Interface>>

parse()1

ContentHandler<<Interface>>

startDocument()startElement()endDocument()endElement()characters()

MyHandler

1

SAXParserFactory

<<creates>>

Parsing Using SAX

DefaultHandler handler = new MyHandler();

SAXParserFactory factory = SAXParserFactory.newInstance();

SAXParser saxParser = factory.newSAXParser();

saxParser.parse( new File("tree.xml"), handler );

A SAX Event Handler

class MyHandler extends DefaultHandler { public void startElement(...) { // start processing detected element } public void endElement(...) { // finish processing detected element } public void characters(...) { // process text element } // etc.}

Creating a DOM Document

Document<<Interface>>

DocumentBuilderFactorynewInstance()

DocumentImpl

DocumentBuildervalidating

parse()

<<creates>>

<<creates>>

DOM Interfaces

Element<<Interface>>

Attr<<Interface>>

CharacterData<<Interface>>

Text<<Interface>>

Document<<Interface>>

Node<<Interface>>

NodeList<<Interface>>

** **

Comment<<Interface>>

CDataSection<<Interface>>

ProcessingInstruction

<<Interface>>

makeDocument(String xmlFile)

// obtain parser factory: DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); //obtain parser: DocumentBuilder builder = factory.newDocumentBuilder(); // parse an xml document into a DOM tree: Document doc = builder.parse(new File(xmlFile));

The Visitor Design Pattern

• Problem: We want to process each node in a tree, but there are many types of nodes.

• Solution: Put the node processing methods in a separate object called a visitor. When a visitor visits a node of type T, the correct method is automatically invoked.Visitors can use depth- or bredth-first traversal

A DOM Visitor

VisitorExceptionVisitor

depthCounter

visit(n : Node)visit(n : Document)visit(n : Text)visit(n : NodeList)visit(n : Element)

SearchVisitorboolean: test(n : Element)visit(n : Element)

PrettyPrintVisitorprefix : String

visit(n : Text)visit(n : Element)

PersonSearchVisitorboolean test(n : Element)

Visiting a Documentpublic class Visitor { protected String name, value; protected int depthCounter = 0; public void visit(Document doc) { try { visit((Node)doc.getDocumentElement()); } catch(VisitorException e) { handle(e); } public void visit(Node node) throws VisitorException { ... } public void visit(NodeList nodes) throws VisitorException { ... } // overridables: protected void visit(Element node) throws VisitorException { } protected void visit(Text node) throws VisitorException { } protected void visit(Attr node) throws VisitorException { } protected void handle(VisitorException e) { System.err.println("visitor exception: " + e); }}

Visiting a Node

public void visit(Node node) throws VisitorException { name = node.getNodeName(); value = node.getNodeValue(); switch (node.getNodeType()) { case Node.ELEMENT_NODE: ... case Node.CDATA_SECTION_NODE: case Node.TEXT_NODE: ... // etc. } // switch} // visit node

Visiting an Element Node: case Node.ELEMENT_NODE: Element elem = (Element) node; depthCounter++; visit(elem); NamedNodeMap attributeNodes = node.getAttributes(); for(int i = 0; i < attributeNodes.getLength(); i++) { Attr attribute = (Attr) attributeNodes.item(i); depthCounter++; visit(attribute); depthCounter--; } depthCounter--; visit(node.getChildNodes()); break;

Visiting Text Nodes

case Node.CDATA_SECTION_NODE: case Node.TEXT_NODE: Text text = (Text) node; depthCounter++; visit(text); depthCounter--; break;

Visiting Child Nodes

public void visit(NodeList nodes) throws VisitorException { for(int i = 0; i < nodes.getLength(); i++) { depthCounter++; visit(nodes.item(i)); depthCounter--; }}

XSLT in JAX

Source<<Interface>>

SAXSource

StreamSource

DOMSource

Result<<Interface>>

StreamResult

SAXResult

DOMResult

Document<<Interface>>

TransformerFactory Transformer

transform(s : Source, r : Result)

<<creates>>

MakeXMLFile()

static public void makeXMLFile(String xmlFile, Document doc) { try { Source xmlSource = new DOMSource(doc); Result result = new StreamResult( new FileOutputStream(xmlFile)); TransformerFactory transFactory = TransformerFactory.newInstance(); Transformer transformer = transFactory.newTransformer(); transformer.setOutputProperty("indent", "yes"); transformer.transform(xmlSource, result); } catch(Exception e) { }}