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Programming with XML. Written by: Adam Carmi Zvika Gutterman. Agenda. About XML Review of XML syntax Document Object Model (DOM) JAXP W3C XML Schema Validating Parsers. About XML. XML – E X tensible M arkup L anguage Designed to describe data - PowerPoint PPT Presentation
Citation preview
Programming with XML
Written by:
Adam Carmi
Zvika Gutterman
XML 2
Agenda
• About XML
• Review of XML syntax
• Document Object Model (DOM)
• JAXP
• W3C XML Schema
• Validating Parsers
XML 3
About XML
• XML – EXtensible Markup Language• Designed to describe data
– Provides semantic and structural information
– Extensible
• Human readable and computer-manipulable• Software and Hardware independent• Open and Standardized by W3C1
• Ideal for data exchange1) World Wide Web Consortium (founded in 1994 by Tim Berners-Lee)
XML 4
Comment
<offenders>
<!-- Lists all traffic offenders -->
<offender id=“024378449 ”>
<firstName> David </firstName>
<middleName>Reuven</middleName>
<lastName>Harel</lastName>
<violation id=’12’>
<code num=“232” category=“traffic”/>
<issueDate>2001-11-02</issueDate>
<issueTime>10:32:00</issueTime>
Ran a red light at Arik & Bentz st.
</violation>
</offender>
</offenders>
offenders.xmlInformation is marked up with structural and semantic information. The characters &, <, >, ‘, “ are reserved and can’t be used in character data. Use &, <, >, ' and " instead.
Tag
CharacterData
CharacterData
XML 5
<offenders>
<!-- Lists all traffic offenders -->
<offender id="024378449 ">
<firstName> David </firstName>
<middleName>Reuven</middleName>
<lastName>Harel</lastName>
<violation id=’12’>
<code num=“232” category=“traffic”/>
<issueDate>2001-11-02</issueDate>
<issueTime>10:32:00</issueTime>
Ran a red light at Arik & Bentz st.
</violation>
</offender>
</offenders>
offenders.xml: Tags
Start Tag
End Tag
Root Tag
Shorthand for:<code num=...></code>
XML tags are not pre-defined and are case sensitive.
An XML document may have only one root tag.
XML 6
<offenders>
<!-- Lists all traffic offenders -->
<offender id="024378449 ">
<firstName> David </firstName>
<middleName>Reuven</middleName>
<lastName>Harel</lastName>
<violation id=’12’>
<code num=“232” category=“traffic”/>
<issueDate>2001-11-02</issueDate>
<issueTime>10:32:00</issueTime>
Ran a red light at Arik & Bentz st.
</violation>
</offender>
</offenders>
offenders.xml: ElementsR
oot
Ele
men
t
Elements mark-up information.
Element x begins with a start-tag <x> and ends with an end-tag </x>
XML Elements must be properly nested:<x>...<y>...</y>...</x>
XML documents must contain exactly one root element.
XML 7
offenders.xml: Content
<offenders> ���<!-- �Lists �all �traffic �offenders �--> ���<offender id="024378449 �"> �����<firstName> ��David �</firstName> �����<middleName>Reuven</middleName> �����<lastName>Harel</lastName> �����<violation id=’12’> �������<code num=“232” category=“traffic”/> �������<issueDate>2001-11-02</issueDate> �������<issueTime>10:32:00</issueTime> �������Ran �a �red �light �at ��Arik �& �Benz st. �����</violation> ���</offender> �</offenders>
The content of an element is all the text that lies between its start and end tags.
An XML parser is required to pass all characters in a document, including whitespace characters.
� whitespace
XML 8
offenders.xml: Attributes
<offenders>
<!-- Lists all traffic offenders -->
<offender id="024378449 ">
<firstName> David </firstName>
<middleName>Reuven</middleName>
<lastName>Harel</lastName>
<violation id=’12’>
<code num=“232” category=“traffic”/>
<issueDate>2001-11-02</issueDate>
<issueTime>10:32:00</issueTime>
Ran a red light at Arik & Benz st.
</violation>
</offender>
</offenders>
Attributes are used to provide additional information about elements.
Attributes values must always be enclosed in quotes (“/‘)
XML 9
DOMTM
• DOMTM – Document Object Model• A Standard hierarchy of objects, recommended by
the W3C, that corresponds to XML documents.• Each element, attribute, comment, etc., in an XML
document is represented by a Node in the DOM tree.
• The DOM API1 allows data in an XML document to be accessed and modified by manipulating the nodes in a DOM tree.
1) Application Programming Interface
XML 10
DOM Class Hierarchy1
1) A partial class hierarchy is presented in this slide.
<<interface>>
Node
<<interface>>
Text
<<interface>>
Element<<interface>>
Document
<<interface>>
Comment
<<interface>>
CharacterData
<<interface>>
NodeList<<interface>>
NamedNodeMap
<<interface>>
Attr
XML 11
offenders.xml: DOM tree:Document
:Elementoffenders
:CommentListsalltrafficoffenders
:Elementoffender
:ElementfirstName :Text
David
:Attributeid
:Text
:Text
:Text
:Text
:Text024378449
XML 12
Example: offenders DOM
:Elementviolation
:Attributeid
:Text
:Elementcode
:Attributenum
:Attributecategory
:Text
:ElementissueDate :Text
2001-11-02
offend
eroffend
ers :Text
12
:Text232
:Texttraffic
:ElementlastName :Text
Harel:Text
The element “middleName”
was skipped
XML 13
Example: offenders DOM
:ElementissueTime :Text
10:32:00
:Text
:TextRanaredlightatArik&Benzst.
offend
er violation
:Text
offend
ers
:Text
XML 14
JAXP
• JAXP – JavaTM API for XML Processing• JAXP enables applications to parse and transform
XML documents using an API that is independent of a particular XML processor implementation.
• JAXP provides two parser types:– SAX1 parser: event driven– DOM document builder: constructs DOM trees
by parsing XML documents.
1) Simple API for XML
XML 15
The Simple API for XML (SAX) APIs
XML 16
The Document Object Model (DOM) APIs
XML 17
Creating a DOM Builder
1. Create a DocumentBuilderFactory object:
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
2. Configure the factory object:
dbf.setIgnoringComments(true);
3. Create a builder instance using the factory:
DocumentBuilder docBuilder =dbf.newDocumentBuilder();
A ParserConfigurationException is thrown if a DocumentBuilder, which satisfies the configuration requested cannot be created.
XML 18
Building a DOM Document
• A DOM document can be built manually from within the application:
Document doc = docBuilder.newDocument();Element offenders = doc.createElement("offenders");doc.appendChild(offenders);Element offender = doc.createElement("offender");offender.setAttribute("id", "024378449 ");offenders.appendChild(offender);Element firstName = doc.createElement(“firstName”);Text text = doc.createTextNode(“ David “);firstName.appendChild(text);...
A DOMException is raised if an illegal character appears in a name, an illegal child is appended to a node etc.
XML 19
Building a DOM Document
• A DOM Tree representation of an XML document can be built automatically by parsing the XML document:
Document doc = docBuilder.parse(new File(xmlFile));
A SAXParseException or SAXException is raised to report parse errors.
XML 20
DumpDom.java (1 of 5)
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.ParserConfigurationException;
import java.io.File;
import java.io.IOException;
Creating and traversing a DOM document
XML 21
DumpDom.java (2 of 5)public class DumpDom { private int indent = 0; // text indentation level public DumpDom(String xmlFile) { try {
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder docBuilder = dbf.newDocumentBuilder(); Document doc = docBuilder.parse(new File(xmlFile)); recursiveDump(doc);
} catch (ParserConfigurationException pce) { System.err.println("Failed to create document builder"); } catch (SAXParseException spe) { System.err.println("Error: Line=" + spe.getLineNumber() + ": " +
spe.getMessage()); } catch (SAXException se) { System.err.println("Parse error found: " + se); } catch (IOException e) { e.printStackTrace(); }
}
XML 22
DumpDom.java (3 of 5) private void recursiveDump(Node node) { switch (node.getNodeType()) { case Node.DOCUMENT_NODE: dumpNode("document", node); break; case Node.COMMENT_NODE: dumpNode("comment", node); break; case Node.ATTRIBUTE_NODE: dumpNode("attribute", node); break; case Node.TEXT_NODE: dumpNode("text", node); break;
XML 23
DumpDom.java (4 of 5) case Node.ELEMENT_NODE: dumpNode("element", node); indent += 2;
NamedNodeMap atts = node.getAttributes(); for (int i = 0 ; i < atts.getLength() ; ++i) recursiveDump(atts.item(i)); indent -= 2; break; default: System.err.println("Unknown node: " + node); System.exit(1); } // end of switch // print children of the input node (if there are any) indent+=2; for (Node child = node.getFirstChild() ; child != null ; child = child.getNextSibling()) { recursiveDump(child); } indent-=2; }// end of recursiveDump
XML 24
DumpDom.java (5 of 5) private void dumpNode(String type, Node node) { for (int i = 0 ; i < indent ; ++i)
System.out.print(" "); System.out.print("[" + type + "]: "); System.out.print(node.getNodeName()); if (node.getNodeValue() != null) System.out.print("=\"" + node.getNodeValue() + "\""); System.out.print("\n");
} public final static void main(String[] args) { DumpDom dumper = new DumpDom(args[0]); }
}
XML 25
DTD - Document Type Definition
• A specification for ensuring the validity of XML documents
• The original mechanism, defined as part of the XML specification
• Various Schema proposals - newer mechanisms for describing validation criteria
XML 26
XML Schema
• The purpose of an XML Schema is to define a class of XML documents.
• An XML document that is syntactically correct is considered well formed. If it also conforms to an XML schema is considered valid.
• An XML document is not required to have a corresponding Schema.
XML 27
XML Schema (cont.)
• XML Schema documents are themselves XML documents.– Can be manipulated as such
– XML Schema is a language with an XML syntax.
• An XML document may explicitly reference the schema document that validates it.
• Several schema models exist. In this course we will use the W3C XML Schema1.
1) W3C recommendation since 2001
XML 28
W3C XML Schema
<xsd:schema xmlns:xsd=“http://www.w3.org/2001/XMLSchema”> ...</schema>
• A W3C XML Schema consists of a schema element and a variety of sub-elements which determine the appearance of elements and their content in instance documents
• Each of the elements (and predefined simple types) in the schema has (by convention) a prefix xsd:which is associated with the W3C XML schema namespace.
XML 29
Elements & Attribute Declarations
• Elements are declared using the element element:<xsd:element name=“firstName” type=“xsd:string”/><xsd:element name=“offenders” type=“Offenders”/>
• Attributes are declared using the attribute element: <xsd:attribute name=“id” type=“xsd:positiveInteger”/>
A pre-defined (simple) type
XML 30
Element & Attribute Types
• Elements that contain sub-elements or carry attributes are said to have complex types.
• Elements that contain only text (e.g. numbers, strings, dates etc.) but do not contain any sub-elements are said to have simple types.
• Attributes always have simple types.• Many simple types (e.g. string, date, integer etc.)
are pre-defined.
XML 31
A Few Built in Simple TypesSimple Type Examples
string any textual value (white space preserved)
NMTOKEN1 student, 342, $$
ID1 s1, :myId, _4
integer -126789, -1, 0, 1, 126789, 03485
float -INF, -1E4, -0, 0,12.78, 12.78E-2, NaN
time 13:24:12, 02:15:34.879
date 2002-11-23
boolean true, false, 0, 1
1) Should only be used as attribute types
XML 32
Derived Simple Types
• New simple types may be defined by deriving them from existing simple types (build-in and derived)
• New simple types are derived by restricting the range of permitted values for an existing simple type.
• A new simple type is defined using the simpleType element.
XML 33
Derived Simple Types (cont.)
• Example: Numeric Restriction <xsd:simpleType name="ViolationID"> <xsd:restriction base="xsd:integer"> <xsd:minInclusive value="100"/> </xsd:restriction></xsd:simpleType>
• Example: Enumeration <xsd:simpleType name="ViolationCategory"> <xsd:restriction base="xsd:string"> <xsd:enumeration value="traffic"/> <xsd:enumeration value="criminal"/> <xsd:enumeration value="civil"/> </xsd:restriction></xsd:simpleType>
XML 34
Complex Types
• Complex types are defined using the complexType element.
• Elements with complex types may carry attributes.• The content of elements with complex types is
categorized as follows:– Empty: no content is allowed.
– Simple: content must be of simple type.
– Element: content must include only child elements.
– Mixed: both element and character content is allowed.
XML 35
Complex Types: Attributes
• Attributes may be declared, using the use attribute, as required or optional (default).
• Default values for attributes are declared using the default attribute– Allowed only for optional attributes
• The fixed attribute is used to ensure that an attribute is set to a particular value.– Appearance of the attribute is optional.– fixed and use are mutually exclusive.
XML 36
Complex Types: Attributes (cont.)
• Example: use, fixed
<xsd:complexType name="Code"> <xsd:attribute name="num" type="ViolationID“ use="required"/> <xsd:attribute name="category" type="ViolationCategory“ fixed="traffic"/></xsd:complexType>
• Example: use, default
<xsd:complexType name="IssueTime"> ...
<xsd:attribute name="accuracy" type="Accuracy" use="optional" default="accurate"/>
...</xsd:complexType>
XML 37
Complex Types: Empty Content
• Example: schema <xsd:complexType name="Code">
<xsd:attribute name="num" type="ViolationID" use="required"/>
<xsd:attribute name="category" type="ViolationCategory“
fixed="traffic"/>
</xsd:complexType>
• Example: instance document<code num="232" category="traffic"/>
<code num="232" category="traffic"></code>
<code num="232"/>
XML 38
Complex Types: Simple Content
• Example: element with no attributes
<xsd:element name="firstName" type="xsd:string"/>
• Example: element with attributes
<xsd:complexType name="IssueTime">
<xsd:simpleContent>
<xsd:extension base="xsd:time">
<xsd:attribute name="accuracy" type="Accuracy" use="optional"
default="accurate"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
Simple type
XML 39
Complex Types: Element Content
• Element Occurrence Constraints– The minimum number of times an element may appear
is specified by the value of the optional attribute minOccurs.
– The maximum number of times an element may appear is specified by the value of the optional attribute maxOccurs.
• The value unbounded indicates that there maximum number of occurrences is unbounded.
– The default value of minOccurs and maxOccurs is 1.
XML 40
Complex Types: Element Content (cont.)
• The element sequence is used to specify a sequence of sub-elements.– Elements must appear in the same order that they are declared.
<xsd:complexType> <xsd:sequence>
<xsd:element name="firstName" type="xsd:string"/> <xsd:element name="middleName" type="xsd:string“
minOccurs="0"/> <xsd:element name="lastName" type="xsd:string"/> <xsd:element name="violation" type="Violation“
minOccurs="0" maxOccurs="unbounded"/> ... </xsd:sequence> ... </xsd:complexType>
XML 41
Complex Types: Mixed Content
• The optional Boolean attribute mixed is used to specify mixed content:
<xsd:complexType name="Violation" mixed="true">
<xsd:sequence>
<xsd:element name="code" type="Code"/>
<xsd:element name="issueDate" type="xsd:date"/>
<xsd:element name="issueTime" type="IssueTime"/>
</xsd:sequence>
...
</xsd:complexType>
XML 42
Global Elements/Attributes• Global elements and global attributes are created
by declarations that appear as the children of the schema element.
• A global element is allowed to appear as the root element of an instance document.
• The attribute ref of element/attribute elements may be used (instead of the name attribute) to reference a global element/attribute.
• Cardinality constraints cannot be placed on global declarations, although they can be placed on local declarations that reference global declarations.
XML 43
Global Elements/Attributes (cont.)
• Example: global declarations
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:element name="offenders" type="Offenders"/>
<xsd:element name="comment" type="xsd:string"/>
<xsd:attribute name="id" type="xsd:positiveInteger"/>
...
• Example: ref attribute
<xsd:element ref="comment" minOccurs="0"/>
<xsd:attribute ref="id" use="required"/>
XML 44
Anonymous Type Definitions
• When a type is referenced only once, or contains very few constraints, it can be more succinctly defined as an anonymous type.
• Saves the overhead of naming the type and explicitly referencing it.
XML 45
Anonymous Type Definitions (cont.)
<xsd:element name="offender" maxOccurs="unbounded"> <xsd:complexType> <xsd:sequence>
<xsd:element name="firstName" type="xsd:string"/> <xsd:element name="middleName" type="xsd:string“
minOccurs="0"/> <xsd:element name="lastName" type="xsd:string"/> <xsd:element name="violation" type="Violation“
minOccurs="0" maxOccurs="unbounded"/> <xsd:element ref="comment" minOccurs="0"/> </xsd:sequence> <xsd:attribute ref="id" use="required"/>
</xsd:complexType></xsd:element>
Is this a global declaration?Anonymous
XML 46
offenders.xsd (1 of 4)<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:element name="offenders" type="Offenders"/> <xsd:element name="comment" type="xsd:string"/> <xsd:attribute name="id" type="xsd:positiveInteger"/>
<xsd:complexType name="IssueTime"> <xsd:simpleContent> <xsd:extension base="xsd:time"> <xsd:attribute name="accuracy" type="Accuracy" use="optional"
default="accurate"/> </xsd:extension> </xsd:simpleContent> </xsd:complexType>
<xsd:complexType name="Code"> <xsd:attribute name="num" type="ViolationID" use="required"/> <xsd:attribute name="category" type="ViolationCategory" fixed="traffic"/> </xsd:complexType>
Schema for offenders
XML documents
XML 47
offenders.xsd (2 of 4) <xsd:complexType name="Offenders"> <xsd:sequence> <xsd:element name="offender" maxOccurs="unbounded"> <xsd:complexType> <xsd:sequence> <xsd:element name="firstName" type="xsd:string"/> <xsd:element name="middleName" type="xsd:string“ minOccurs="0"/> <xsd:element name="lastName" type="xsd:string"/> <xsd:element name="violation" type="Violation" minOccurs="0" maxOccurs="unbounded"/> <xsd:element ref="comment" minOccurs="0"/> </xsd:sequence> <xsd:attribute ref="id" use="required"/> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType>
XML 48
offenders.xsd (3 of 4) <xsd:complexType name="Violation" mixed="true"> <xsd:sequence> <xsd:element name="code" type="Code"/> <xsd:element name="issueDate" type="xsd:date"/> <xsd:element name="issueTime" type="IssueTime"/> </xsd:sequence> <xsd:attribute ref="id" use="required"/> </xsd:complexType>
<xsd:simpleType name="ViolationID"> <xsd:restriction base="xsd:integer"> <xsd:minInclusive value="100"/> </xsd:restriction> </xsd:simpleType>
XML 49
offenders.xsd (4 of 4) <xsd:simpleType name="ViolationCategory"> <xsd:restriction base="xsd:string"> <xsd:enumeration value="traffic"/> <xsd:enumeration value="criminal"/> <xsd:enumeration value="civil"/> </xsd:restriction> </xsd:simpleType> <xsd:simpleType name="Accuracy"> <xsd:restriction base="xsd:string"> <xsd:enumeration value="accurate"/> <xsd:enumeration value="approx"/> </xsd:restriction> </xsd:simpleType>
</xsd:schema>
XML 50
Validating Parsers
• A validating parser is capable of reading a Schema specification or DTD and determine whether or not XML documents conform to it.
• A non validating parser is capable of reading a Schema / DTD but cannot check XML documents for conformity.– Limited to syntax checking
XML 51
Creating a Validating DOM Parser
1. Create a DocumentBuilderFactory object:
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
2. Configure the factory object to produce a validating parser:
dbf.setAttribute("http://java.sun.com/xml/jaxp/properties" + "/schemaLanguage", "http://www.w3.org/2001/XMLSchema");dbf.setAttribute("http://java.sun.com/xml/jaxp/properties" + "/schemaSource", new File(xmlSchema));dbf.setValidating(true);
3. Create a builder instance and set its error-handler:
DocumentBuilder docBuilder = dbf.newDocumentBuilder();docBuilder.setErrorHandler(new MyErrorHandler());
XML 52
Handling Parsing Errors
• By default, JAXP parsers do not throw exceptions when documents are found to be invalid.
• JAXP provides the interface ErrorHandler so that users will be able to implement their own error-handling semantics.
XML 53
BoundedErrorPrinter.java (1 of 3)
import org.xml.sax.ErrorHandler;import org.xml.sax.SAXException;import org.xml.sax.SAXParseException;
/** * An error handler that prints to the standard error stream a specified * number of errors. Once the specified number of errors is detected, * parsing is aborted. */public class BoundedErrorPrinter implements ErrorHandler { private int errorCount = 0; private int errorsToPrint; public BoundedErrorPrinter(int errorsToPrint) {
this.errorsToPrint = errorsToPrint; }
XML 54
public void warning(SAXParseException spe) throws SAXException
{
System.err.println("Warning: " + getParseExceptionInfo(spe));
}
public void error(SAXParseException spe) throws SAXException
{
if (errorCount < errorsToPrint) {
System.err.println("Error: " + getParseExceptionInfo(spe));
++errorCount;
}
if (errorCount >= errorsToPrint)
throw spe; // abort parsing
}
BoundedErrorPrinter.java (2 of 3)
XML 55
public void fatalError(SAXParseException spe) throws SAXException { if (errorCount < errorsToPrint)
System.err.println("Fatal: " + getParseExceptionInfo(spe)); throw spe; }
public boolean errorsFound() {
return errorCount > 0; }
private String getParseExceptionInfo(SAXParseException spe) { return "Line = " + spe.getLineNumber() + ": " + spe.getMessage(); }}
BoundedErrorPrinter.java (3 of 3)