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Processing XML with Java

Processing XML with Java. A comprehensive tutorial about XML processing with Java XML tutorial of W3Schools. Parsers. What is a parser?. Formal grammar. Analyzed Data. Input. Parser.

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Processing XML with Java

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  1. Processing XML with Java A comprehensive tutorial about XML processing with Java XML tutorial of W3Schools

  2. Parsers • What is a parser? Formal grammar Analyzed Data Input Parser The structure(s) of the input, according to the atomic elements and their relationships (as described in the grammar)

  3. XML-Parsing Standards • We will consider two parsing methods that implement W3C standards for accessing XML • DOM • convert XML into a tree of objects • “random access” protocol • SAX • “serial access” protocol • event-driven parsing

  4. XML Examples

  5. root element world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries> validating DTD file reference to an entity

  6. XML Tree Model element element attribute simple content

  7. world.dtd <!ELEMENTcountries(country*)> <!ELEMENTcountry(name,population?,city*)> <!ATTLISTcountrycontinentCDATA#REQUIRED> <!ELEMENTname (#PCDATA)> <!ELEMENTcity (name)> <!ATTLISTcitycapital(yes|no) "no"> <!ELEMENTpopulation (#PCDATA)> <!ATTLISTpopulationyearCDATA#IMPLIED> <!ENTITYeu"Europe"> <!ENTITYas"Asia"> <!ENTITY af"Africa"> <!ENTITY am"America"> <!ENTITY au"Australia"> parsed Not parsed default value As opposed to required Open world.xml in your browser Check world2.xml for #PCDATA exmaple

  8. Namespaces sales.xml <?xml version="1.0"?> <forsale date="12/2/03" xmlns:xhtml="http://www.w3.org/1999/xhtml"> <book> <title> <xhtml:em>DBI:</xhtml:em> <![CDATA[Where I Learned <xhtml>.]]> </title> <comment xmlns="http://www.cs.huji.ac.il/~dbi/comments"> <par>My <xhtml:b> favorite </xhtml:b> book!</par> </comment> </book> </forsale> “xhtml” namespace declaration (non-parsed) character data namespace overriding default namespace declaration

  9. sales.xml <?xml version="1.0"?> <forsale date="12/2/03" xmlns:xhtml="http://www.w3.org/1999/xhtml"> <book> <title> <xhtml:h1> DBI </xhtml:h1> <![CDATA[Where I Learned <xhtml>.]]> </title> <comment xmlns="http://www.cs.huji.ac.il/~dbi/comments"> <par>My <xhtml:b> favorite </xhtml:b> book!</par> </comment> </book> </forsale> Namespace:“http://www.w3.org/1999/xhtml” Local name: “h1” Qualified name:“xhtml:h1”

  10. sales.xml <?xml version="1.0"?> <forsale date="12/2/03" xmlns:xhtml="http://www.w3.org/1999/xhtml"> <book> <title> <xhtml:h1> DBI </xhtml:h1> <![CDATA[Where I Learned <xhtml>.]]> </title> <comment xmlns="http://www.cs.huji.ac.il/~dbi/comments"> <par>My <xhtml:b> favorite </xhtml:b> book!</par> </comment> </book> </forsale> Namespace:“http://www.cs.huji.ac.il/~dbi/comments” Local name:“par” Qualified name:“par”

  11. sales.xml <?xml version="1.0"?> <forsale date="12/2/03" xmlns:xhtml="http://www.w3.org/1999/xhtml"> <book> <title> <xhtml:h1>DBI</xhtml:h1> <![CDATA[Where I Learned <xhtml>.]]> </title> <comment xmlns="http://www.cs.huji.ac.il/~dbi/comments"> <par>My <xhtml:b> favorite </xhtml:b> book!</par> </comment> </book> </forsale> Namespace: “” Local name:“title” Qualified name:“title”

  12. sales.xml <?xml version="1.0"?> <forsale date="12/2/03" xmlns:xhtml="http://www.w3.org/1999/xhtml"> <book> <title> <xhtml:h1>DBI</xhtml:h1> <![CDATA[Where I Learned <xhtml>.]]> </title> <comment xmlns="http://www.cs.huji.ac.il/~dbi/comments"> <par>My <xhtml:b> favorite </xhtml:b> book!</par> </comment> </book> </forsale> Namespace:“http://www.w3.org/1999/xhtml” Local name:“b” Qualified name:“xhtml:b”

  13. DOM – Document Object Model

  14. DOM Parser • DOM = Document Object Model • Parser creates a tree object out of the document • User accesses data by traversing the tree • The tree and its traversal conform to a W3C standard • The API allows for constructing, accessing and manipulating the structure and content of XML documents

  15. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries>

  16. The DOM Tree

  17. Application API XML File DOM Parser DOM Tree Using a DOM Tree in memory

  18. Creating a DOM Tree • A DOM tree is generated by a DocumentBuilder • The builder is generated by a factory, in order to be implementation independent • The factory is chosen according to the system configuration DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); Document doc = builder.parse("world.xml");

  19. Configuring the Factory • The methods of the document-builder factory enable you to configure the properties of the document building • For example • factory.setValidating(true) • factory.setIgnoringComments(false) Read more about DocumentBuilderFactory Class, DocumentBuilder Class

  20. The Node Interface • The nodes of the DOM tree include • a special root (denoted document) • The Document interface retrieved by builder.parse(…) actually extends the Node Interface • element nodes • text nodes and CDATA sections • attributes • comments • and more ... • Every node in the DOM tree implements the Node interface This is very unintuitive (some would even say this is a bloated design)

  21. Figure as appears in : “The XML Companion” - Neil Bradley NodeList NamedNodeMap A light-weight fragment of the document. Can hold several sub-trees Interfaces in a DOM Tree DocumentFragment Document Text CDATASection CharacterData Comment Attr Element Node DocumentType Notation Entity EntityReference Run FragmentVsElement with 1st argument fragment/element ProcessingInstruction DocumentType

  22. Document Type Element Attribute Attribute Element Element Text Text Element Entity Reference Text Text Comment Text Interfaces in the DOM Tree Document

  23. Node Navigation • Every node has a specific location in tree • Node interface specifies methods for tree navigation • Node getFirstChild(); • Node getLastChild(); • Node getNextSibling(); • Node getPreviousSibling(); • Node getParentNode(); • NodeList getChildNodes(); • NamedNodeMap getAttributes()

  24. Node Navigation (cont) getPreviousSibling() getFirstChild() getChildNodes() getParentNode() getLastChild() getNextSibling()

  25. Not a very OO approach… reminds one of simulating OO using unions in C…. Node Properties Only Element Nodes have attributes… some would say this should’ve been a property of the Element derived class and not of Node. • Every node has (a dubious design and…) • a type • a name • a value • attributes • The roles of these properties differ according to the node types • Nodes of different types implement different interfaces (that extend Node) Very few nodes have both a significant name and a significant value

  26. Names, Values and Attributes

  27. Node Types - getNodeType() ELEMENT_NODE = 1 ATTRIBUTE_NODE = 2 TEXT_NODE = 3 CDATA_SECTION_NODE = 4 ENTITY_REFERENCE_NODE = 5 ENTITY_NODE = 6 PROCESSING_INSTRUCTION_NODE = 7 COMMENT_NODE = 8 DOCUMENT_NODE = 9 DOCUMENT_TYPE_NODE = 10 DOCUMENT_FRAGMENT_NODE = 11 NOTATION_NODE = 12 if (myNode.getNodeType() == Node.ELEMENT_NODE) { //process node … } Read more about Node Interface

  28. import org.w3c.dom.*; import javax.xml.parsers.*; publicclass EchoWithDom { publicstaticvoid main(String[] args) throwsException { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); factory.setIgnoringElementContentWhitespace(true); DocumentBuilder builder = factory.newDocumentBuilder(); Document doc = builder.parse(“world.xml"); new EchoWithDom().echo(doc); } e.g white spaces used for indentation in non mixed data elements

  29. privatevoid echo(Node n) { print(n); if (n.getNodeType() == Node.ELEMENT_NODE) { NamedNodeMap atts = n.getAttributes(); ++depth; for (int i = 0; i < atts.getLength(); i++) echo(atts.item(i)); --depth; } depth++; for (Node child = n.getFirstChild(); child != null; child = child.getNextSibling()) echo(child); depth--; } Attribute nodes are not included…

  30. privateint depth = 0; privateString[] NODE_TYPES = { "", "ELEMENT", "ATTRIBUTE", "TEXT", "CDATA", "ENTITY_REF", "ENTITY", "PROCESSING_INST", "COMMENT", "DOCUMENT", "DOCUMENT_TYPE", "DOCUMENT_FRAG", "NOTATION" }; privatevoid print(Node n) { for (int i = 0; i < depth; i++) System.out.print(" "); System.out.print(NODE_TYPES[n.getNodeType()] + ":"); System.out.print("Name: "+ n.getNodeName()); System.out.print(" Value: "+ n.getNodeValue()+"\n"); }} run EchoWithDom, pay attention to the default values

  31. Another Example publicclass WorldParser { publicstaticvoid main(String[] args) throwsException { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); factory.setIgnoringElementContentWhitespace(true); DocumentBuilder builder = factory.newDocumentBuilder(); Document doc = builder.parse("world.xml"); printCities(doc); }

  32. Another Example (cont) publicstaticvoid printCities(Document doc) { NodeList cities = doc.getElementsByTagName("city"); for(int i=0; i<cities.getLength(); ++i) { printCity((Element)cities.item(i)); } } publicstaticvoid printCity(Element city) { Node nameNode = city.getElementsByTagName("name").item(0); String cName = nameNode.getFirstChild().getNodeValue(); System.out.println("Found City: " + cName); } Searches within descendents run WorldParser

  33. Normalizing the DOM Tree • Normalizing a DOM Tree has two effects: • Combine adjacent textual nodes • Eliminate empty textual nodes • To normalize, apply the normalize() method to the document element Created by node manipulation…

  34. Node Manipulation • Children of a node in a DOM tree can be manipulated - added, edited, deleted, moved, copied, etc. • To constructs new nodes, use the methods of Document • createElement,createAttribute, createTextNode, createCDATASection etc. • To manipulate a node, use the methods of Node • appendChild, insertBefore, removeChild,replaceChild, setNodeValue, cloneNode(boolean deep)etc.

  35. Figure as appears in “The XML Companion” - Neil Bradley Old New New Ref insertBefore replaceChild deep = 'false' cloneNode deep = 'true' Node Manipulation (cont)

  36. SAX – Simple APIfor XML

  37. SAX Parser • SAX = Simple API for XML • XML is read sequentially • When a parsing event happens, the parser invokes the corresponding method of the corresponding handler. • This is called event-driven programming. Most GUI programs are written using this paradigm. • The handlers are programmer’s implementation of standard Java API (i.e., interfaces and classes)

  38. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <!--israel--> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries>

  39. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <!--israel--> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries> Start Document

  40. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <!--israel--> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries> Start Element

  41. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <!--israel--> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries> Start Element

  42. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <!--israel--> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries> Comment

  43. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <!--israel--> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries> Start Element

  44. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <!--israel--> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries> Characters

  45. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <!--israel--> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries> End Element

  46. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <!--israel--> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries> End Element

  47. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <!--israel--> <name>Israel</name> <population year="2001">6,199,008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60,424,213</population> </country> </countries> End Document

  48. <?xml version="1.0"?> . . . SAX Parsers When you see the start of the document do … SAX Parser When you see the start of an element do … When you see the end of an element do …

  49. Used to create a SAX Parser Handles document events: start tag, end tag, etc. Handles Parser Errors Handles DTD Handles Entities

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