CSE603 Management of Semistructured Data 04. DOM & SAX

Transcription

1 CSE603 Management of Semistructured Data 04. DOM & SAX Scott Lee Hanyang University ERICA Campus 2 nd Semester 2014

2 Document Object Model DOM DOM : Document Object Model W3C recommandation (3 level) Core / XML / HTML platform and language-neutral data model and API for programmatic access and manipulation of XML and HTML in-memory & hierarchical tree-like data structure object-oriented : provides objects and properties for all document elements and the methods to access them enables programs/scripts to dynamically navigate, get, add, update, delete XML elements

3 Document Object Model Node everything in XML document is represented as a Node

4 Document Object Model Node tree

5 Document Object Model DOM tree representation DOM tree - structural representation :

6 Document Object Model XML processing Generic form of XML processing with DOM :

7 Java API for XML Processing JAXP Provides common interface for creating and using the standard DOM, SAX and XSLT APIs in Java. All JAXP packages are included standard in JDK 1.4+ Key packages : javax.xml.parsers : The main APIs providing common interface for various DOM and SAX parsers org.w3c.dom : Defines the Document class (DOM) & classes for all the components of a DOM org.xml.sax : Defines the basic SAX APIs javax.xml.transform : Defines the XSLT APIs that let you transform XML into other forms Importing necessary classes to parse XML with JAXP DOM : import javax.xml.parsers.*; import org.w3c.dom.*...

8 Parsing XML with JAXP DOM javax.xml.parsers defines : DocumentBuilderFactory : creates an instance of the parser determined by the system property DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance() ; DocumentBuilder : defines the API to obtain DOM Document DocumentBuilder builder = factory.newdocumentbuilder() ; Document : DOM containing the entire XML document document = builder.parse(new File("test.xml"))

9 Node Methods Operations on Nodes : getnodename() : Element tag name Text "#text" Attribute name of attribute getnodevalue() : Element null Text text contents Attribute value of attribute getnodetype() : Element ELEMENT NODE Text TEXT NODE Attribute ATTRIBUTE NODE getattributes() : Element NamedNodeMap Text null Attribute null

10 Node Methods e.g., Distinguish Node Types switch(node.getnodetype()) { case Node.ELEMENT NODE : Element element = (Element)node;...; break; case Node.TEXT NODE : Text text = (Text)node;...; break; case Node.ATTRIBUTE NODE : Attr attr = (Attr)node;...; break; default :... }

11 Node Methods Tree-walking operations returning a Node : getparentnode() : returns the parent node getfirstchild() : returns the node of the first child getlastchild() : returns the last child getprevioussibling() : returns the node immediately preceding getnextsibling() : returns the node immediately next to Test operations returning a boolean : hasattributes() : returns true if the node has attributes, false otherwise haschildnodes() : return true if the node has children, false otherwise

12 Element Methods String gettagname() returns the name of the tag boolean hasattributes(string name) returns true if this Element has the named attribute String getarrtibue(string name) returns the value(string) of the named attribute boolean hasattribute() returns true if this Element has an attributes this method is inherited from Node - returns false if it is applied to a Node that is not an Element NamedNodeMap getattributes() returns NamedNodeMap of all the Element s attributes this method is inherited from Node - returns false if it is applied to a Node that is not an Element

13 NodeList & NamedNodeMap NodeList ordered list of nodes can be accessed through index Operations on NodeList : item(int index) : returns the index th item NamedNodeMap unordered list of nodes can be accessed through both name and index Operations on NamedNodeMap : getnameditem(string name) : returns the attribute with the given name (as a Node) getlength() : returns the number of nodes within item(int index) : returns the index th item

14 Text Methods Text is subinterface of CharacterData and inherits the following operations: String getdata() : returns the text contents int getlength() : returns the number of characters in the text String substringdata(int offset, int count) : returns the substring of the text contents...

15 Attribute Methods Operations on Attrs : String getname() : returns the attribute name Element getownerelement() : returns the Element node the attribute belongs to or null if the attribute is not in use boolean getspecified() : returns true if the attribute was explicity given a value in the original document String getvalue() : returns the vaue of the attribute as a String...

16 DOM Traversal Preorder Traversal Preorder DOM traversal : visit root traverse each subtree in order static void preordertprint(string indent, Node node){ printnode(indent, node); if (node.haschildnodes()){ Node child = node.getfirstchild(); while (child!= null) { preordertprint(indent + " ", child); child = child.getnextsibling(); } } } static void printnode(string indent, Node node){ System.out.println(indent + node.getnodetype() + " " + node.getname + " " + node.getvalue() + " " + node.getattributes()) }

17 Methods used for Building DOM tree builder.newdocument() document.createelement(string s) document.createtextnode(string s) document.createcdatasection(string s) document.createcomment(string s) Node.appendChild(Node n) Node.insertBefore(Node newnode, Node n)... document.createattribute(string s) Node.setAttributeNode(Attr a)... TextNode.insertData(int Offset, String s)...

18 Methods used for Manipulating DOM tree Node.nodeValue = String s : (TextNode, Attribute, etc) Node.setAttribute(String attrname, String s) Node.replaceChild(Node newnode, Node n) TextNode.replaceData(int offset, int length, String s) :(TextNode)... Node.removeChild(Node n) Node.removeAttribute(String s) Node.removeAttributeNode(Attr a)... Node.cloneNode(true)...

19 DOM Properties & Methods Study the properties & methods of the following entities in DOM Node Types : types for nodes representing different XML entities in DOM tree Node : single node of Node Type in DOM tree Document : node representing the entire XML document Element : node representing an Element in XML Attribute : node representing an attribute in XML Text : node representing textual content of element or attribute CDATA : node representing CDATA in XML Comment : node representing comments in XML NodeList : ordered list of nodes NamedNodeMap : unordered list of nodes...

20 Summary of DOM DOM : Document Object Model W3C recommendations for accessing and manipulating XML document (platform and language neutral) all XML entities are represented using Node in tree-structure (Document, Element, Text, etc) parent, child and sibling is used to specify relationship between nodes (DOM tree(xml) can be navigated with these relationships) DOM-based parsers are available for most of browsers and applications properties and methods are used to access and manipulate nodes (important properties: nodename, nodevalue, nodetype) properties and methods such as childnodes or getelementsbytagname() returns NodeList Study properties and methods of different nodes in DOM Study various DOM examples and do on-line exercises

21 Simple API for XML SAX SAX : Simple API for XML Event-based Interface sends events to the application as document is read startelement : bank characters : HY Bank endelement : bank does not create data structure Versions & SAX 2.0 (2000) SAX 1.0 (1998) SAX 2.0 (2000) - namespace support - external entity support -...

22 Simple API for XML (SAX) Pros & Cons Pros can parse document with any size (large document) can build own data structure (e.g, with higher level objects) can ignore unwanted data (when small subset of info wanted) simple & fast Cons random access is not possible complex search is difficult does not remember previous event without an explicit code document modification is difficult

23 Simple API for XML (SAX) Interface Structure SAX Interface DocumentHandler : to process document events DTDHandler : to process DTD event ErrorHandler : to process error events EntityResolver : to customize external entity SAX Events startdocument() startelement() characters() endelement() enddocument() processinginstruction()

24 Java API for XML Processing JAXP provides interface for SAX 1.0 & SAX 2.0

25 Parsing XML with JAXP SAX Creating an event handler (Default Handler) - event handler must be created before application to use SAX to process an XML document import org.xml.sax.helpers.defaulthandler; public class ehandler extends DefaultHandler {...} Creating a SAX parser using JAXP - use SAXParser & SAXParserFactory class and get XMLReader import javax.xml.parsers.saxparser; import javax.xml.parsers.saxparserfactory; import org.xml.sax.xmlreader; SAXParserFactory spfactory = SAXParserFactory.newInstance(); SAXParser saxparser = spfactory.newsaxparser(); XMLReader xmlreader = saxparser.getxmlreader();

26 Parsing XML with JAXP SAX Set validation option (turn off if there is no DTD or schema) spfactory.setvalidating(false); Set content handler xmlreader.setcontenthandler(new ehandler); Parse InputSource InputSource source = new InputSource("document.xml"); xmlreader.parse(source);

27 Parsing XML with JAXP SAX Create ErrorHandler (error, warning, fatalerror) import org.xml.sax.saxparseexception; public void error(saxparseexception e) {...} public void warning(saxparseexception e) {...} public void fatalerror(saxparseexception e) {...} Set ErrorHandler (in main method) xmlreader.seterrorhandler(new ehandler());

28 Parsing XML with JAXP SAX SAX Events startdocument() & enddocument() public void startdocument() throws SAXException{...} public void enddocument() throws SAXException{...} startelement() public void startelement(string namespaceuri, String localname, String qname, Attributes atts) throws SAXException{ for(int a = 0, a < atts.getlength(), a++) { String attname = atts.getlocalname(a); String attvalue = atts.getvalue(attname); } }

29 Parsing XML with JAXP SAX SAX Events endelement() public void endelement(string namespaceuri, String localname, String qname) throws SAXException{...} characters() public void characters(char characters[], int start, int length) throws SAXException{...} processinginstruction() public void processinginstruction(string target, String data) throws SAXException{...}

30 Parsing XML with JAXP SAX Support for Namespaces startelement() public void startelement(string namespaceuri, String localname, String qname, Attributes atts) throws SAXException{... if (namespaceuri == "...") { String atturi = atts.geturi(); String attqname = atts.getqname(i);... } }

31 Summary of SAX SAX : Simple API for XML vendor-neutral standard event-based interface : processes elements, attribute and other data as it appears in XML documents read-only system faster and more lightweight when compared to DOM utilizes different handler interfaces with various SAX events when parsing XML documents Study various SAX examples and do on-line exercises