Content of this lecture. Some Tools for Handling XML Documents XML. Schema and XML

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1 Content of this lecture Some Tools for Handling XML Documents Birgit Grohe A convenient Java-tool: (Java Architecture for XML Binding) A more advanced Java tool: A simple tool for small projects: Regular expressions (Java or Perl) 1 2 XML XML: extensible Markup Language Used to store and transfer data in applications when it is important that the data has a particular structure. Many programming languages/applications provide tools to validate the structure of an XMLfile against a schema. Schema and XML Schema is a language for describing structures. XML is a language for describing instances with these structures. po.xsd Validitation Tools po.xml The Schema Primer 3 Describes how e.g. a purchase order document is structured. Uses the elements defined in the schema to describe a particular purchase order. 4 1

2 : Java Architecture for XML Binding allows Java developers to access and process xml data without having to know XML or xml processing. xml schema binding compiler Application Schemaderived classes & interfaces Miracle tool? xml document API Content objects marshal unmarshal 5 6 : Example Packages: javax.xml.bind: classes and interfaces for unmarshalling, marshalling, and validation etc. javax.xml.bind.util, javax.xml.bind.helper Requirements: An XML document and a schema. The schema must be written in the W3C XML Schema Language. Given an xml-file books.xml and a schemabooks.xsd that contains the main element BookList and several subelements and element types, e.g. BookType. The example wants to give you small glimts of what is possible with. All details can be found on the oracle webpage, see slide 5! 7 8 2

3 : Example Binding a schema (= generates a set of interfaces and classes that implement the interfaces) gives: BookListType.java interface for the unnamed complex type <BookList> BookList.java inteface for the element <BookList> BookType.java: for the complex type <BookType>. ObjectFactory.java: Contains methods for generating instances of the interfaces. impl/booktype.java: class that implements the interface... Now we can complile these classes! 9 : Example Unmarshal: Extract information from an xml file: import javax.xml.bind.context; import javax.xml.bind.unmarshaller; Object context path Context jc = Context.newInstance(.."); Unmarshaller unmarshaller = jc.createunmarshaller(); BookList blist= (BookList) unmarshaller.unmarshal(new File( "books.xml")); BookListType.BookType booktype = blist.getbooks(); List booklist = booktype.getbook(); Access elements and their content! Marshal and validate work similarly. 10 SAX Parser If there is no schema? With some extra effort, it is possible to create your own parser in Java using the SAX Parser and associated classes and interfaces. SAX tutorial: parser1.sql&id= SAXParser: An Example import java.io.*; import org.xml.sax.*; import javax.xml.parsers.saxparserfactory; import javax.xml.parsers.saxparser; import... public class BooksLibrary extends HandlerBase {...} public static void main (String argv []) { SAXParserFactory factory = SAXParserFactory.newInstance(); try { out = new OutputStreamWriter (System.out, "UTF8"); SAXParser saxparser = factory.newsaxparser(); saxparser.parse( new File(XML_FILE_NAME), new BooksLibrary()); } catch (Throwable err) { err.printstacktrace ();} } Create a new instance of SAXParserFactory Get a new SAXParser 12 3

4 SAXParser: An Example Among others, following methods from the interface DocumentHandlerBase have to be implemented: public void startdocument () throws SAXException {...} public void enddocument () throws SAXException {...} public void startelement (String name, AttributeList attrs) throws SAXException {...} public void endelement (String name) throws SAXException {...}... Only recommended if you have prior experience in Java. 13 More Java Parsers Java offers a number of different parsers for handling xml-documents: DOM (Document Object Model) Parser XSLT (XML Style Sheet) Parsers XML Parser tutorial parsers.sql&id= XML and Regular Expressions XML and Regular Expressions Regular expressions can be used to easily extract information from xml-files. If the structure of the xml-file is known, the startand end-tags can be used to filter the desired content. Suitable for small and simple projects. Example: Given an xml-file with a booklist that has elements <book> which in turn have elements <Title> and <Author>: 15 <book> <Title>Introduction to Algorithms</Title> <Author>Cormen</Author> </book> while (<FILE>){ my $found = 0; if ( /Title/){$found = 1;} = split /(<Title>) (<\/Title>)/, $_; if( $found $fields[3];} } The fields-index may depend on the details of the xml-file. 16 4

5 Summary XML-Tools For small och simpler tasks, and if you are not familiar with using more advanced Java classes and interfaces: Use regular expressions! If there is a schema, and the task involves a large part of the content of the xml-file, it is worth learning the -tool. If there is no schema, and you are famliar with Java, you can try the Java xml-parser tools such as the SAXParser. If there is no schema, but some data type definition (DTD) files instead, you may find tools to produce a schema. 17 5