1. ©1996-2000 jGuru.com XML and Java Alex Chaffee, alex@jguru.com http://www.purpletech.com

2. Overview Why Java and XML? Parsers: DOM, JDOM, SAX Using XML from JSP Java/XML Object Mapping Resources

3. Why Java/XML? XML maps well to Java –late binding –hierarchical (OO) data model Unicode support in Java XML Structures map well to Java Objects Portability Network friendly

4. XML Parsers Validating/Non-Validating Tree-based Event-based SAX-compliance Not technically parsers –XSL –XPath

5. Some Java XML Parsers DOM –Sun JAXP –IBM XML4J –Apache Xerces –Resin (Caucho) –DXP (DataChannel) SAX –Sun JAXP –SAXON JDOM

6. Dom API Tree-based Node classes Part of W3C spec Sorting/Modifying of Elements Sharing document with other applications

7. XML is a Tree Scrambled Eggs Hash Browns Orange Juice Chips menu meal name "breakfast" food "Scrambled Eggs" food "Hash Browns" drink "Orange Juice" meal

8. DOM API (cont’d) Based on Interfaces –Good design style - separate interface from implementation –Document, Text, Processing Instruction, Element - ALL are interfaces –All extend interface Node –Including interface Attr (parentNode is null, etc)

9. public void print(Node node) { //recursive method call using DOM API... int type = node.getNodeType(); case Node.ELEMENT_NODE: // print element with attributes out.print('<'); out.print(node.getNodeName()); Attr attrs[] = node.getAttributes(); for (int i = 0; i < attrs.length; i++) { Attr attr = attrs[i]; out.print(' '); out.print(attr.getNodeName());out.print("=\""); out.print(normalize(attr.getNodeValue())); out.print('"'); } out.print('>'); NodeList children = node.getChildNodes(); if (children != null) { int len = children.getLength(); for (int i = 0; i < len; i++) { print(children.item(i)); } break; case Node.ENTITY_REFERENCE_NODE: // handle entity reference nodes //... DOM Example

10. DOM API Highlights Node –getNodeType() –getNodeName() –getNodeValue() returns null for Elements –getAttributes() returns null for non-Elements –getChildNodes() –getParentNode() Element –getTagName() same as getNodeName() –getElementsByTagName(String tag) get all children of this name, recursively –normalize() smooshes text nodes together Attr –attributes are not technically child nodes –getParent() et al. return null –getName(), getValue() Document –has one child node - the root element call getDocumentElement() –contains factory methods for creating attributes, comments, etc.

11. DOM Level 2 Adds namespace support, extra methods Not supported by Java XML processors yet

12. The Trouble With DOM Written by C programmers Cumbersome API –Node does double-duty as collection –Multiple ways to traverse, with different interfaces Tedious to walk around tree to do simple tasks Doesn't support Java standards (java.util collections)

13. JDOM: Better than DOM Java from the ground up Open source Clean, simple API Uses Java Collections

14. JDOM vs. DOM Classes / Interfaces Java / Many languages Java Collections / Idiosyncratic collections getChildText() and other useful methods / getNextSibling() and other useless methods

15. JDOM: The Best of Both Worlds Clean, easy to use API –document.getRootElement().getChild("book"). getChildText("title") Random-access tree model (like DOM) Can use SAX for backing parser Open Source, not Standards Committee –Allowed benevolent dictatorship -> clean design

16. XMLOutputter out = new XMLOutputter(); out.output( element, System.out ); Or… public void print(Element node) { //recursive method call using JDOM API... out.print('<'); out.print(node.getName()); List attrs = node.getAttributes(); for (int i = 0; i < attrs.size(); i++) { Attribute attr = (Attribute)attrs.get(i); out.print(' '); out.print(attr.getName());out.print("=\""); out.print(attr.getValue() ); out.print('"'); } out.print('>'); List children = node.getChildren(); if (children != null) { for (int i = 0; i < children.size(); i++) { print(children.item(i)); } JDOM Example

17. public Element toElement(User dobj) throws IOException { User obj = (User)dobj; Element element = new Element("user"); element.addAttribute("userid", ""+user.getUserid()); String val; val = obj.getUsername(); if (val != null) { element.addChild(new Element("username").setText(val)); } val = obj.getPasswordEncrypted(); if (val != null) { element.addChild(new Element("passwordEncrypted").setText(val)); } return element; }

18. JDOM Example public User fromElement(Element element) throws DataObjectException { List list; User obj = new User(); String value = null; Attribute userid = element.getAttribute("userid"); if (userid != null) { obj.setUserid( userid.getIntValue() ); } value = element.getChildText("username"); if (value != null) { obj.setUsername( value ); } value = element.getChildText("passwordEncrypted"); if (value != null) { obj.setPasswordEncrypted( value ); } return obj; }

19. DOMUtils DOM is clunky DOMUtils.java - set of utilities on top of DOM http://www.purpletech.com/code Or just use JDOM

20. Event-Based Parsers Scans document top to bottom Invokes callback methods Treats XML not like a tree, but like a list (of tags and content) Pro: –Not necessary to cache entire document –Faster, smaller, simpler Con: –must maintain state on your own –can't easily backtrack or skip around

21. SAX API Grew out of xmldev mailing list (grassroots) Event-based startElement(), endElement() Application intercepts events Not necessary to cache entire document

22. Sax API (cont’d) public void startElement(String name, AttributeList atts) { // perform implementation out.print(“Element name is “ + name); out.print(“, first attribute is “ + atts.getName(0) + “, value is “ + atts.getValue(0)); }

23. XPath The stuff inside the quotes in XSL Directory-path metaphor for navigating XML document –"/curriculum/class[4]/student[first()]" Implementations –Resin (Caucho) built on DOM –JDOM has one in the "contrib" package Very efficient API for extracting specific info from an XML tree –Don't have to walk the DOM or wait for the SAX –Con: yet another syntax / language, without full access to Java libraries

24. XSL eXtensible Stylesheet Language transforms one XML document into another XSL file is a list of rules Java XSL processors exist –Apache Xalan (not to be confused with Apache Xerces) –IBM LotusXSL –Resin –SAXON –XT

25. Trouble with XSL It's a programming language masquerading as a markup language Difficult to debug Turns traditional programming mindset on its head –Declarative vs. procedural –Recursive, like Prolog Doesn't really separate presentation from code

26. JSP JavaServer Pages Outputting XML <% User = loadUser(request.getParameter("username")); response.setContentType("text/xml"); %> Can also output HTML based on XML parser, naturally (see my "JSP and XML" talk, or http://www.purpletech.com)

27. XMLC A radical solution to the problem of how to separate presentation template from logic… …to actually separate the presentation template from the logic!

28. XMLC Architecture HTML (with ID tags) Java Class (e.g. Servlet) HTML Object (automatically generated) XMLC HTML (dynamically-generated) Setting values Data Reading data

29. XMLC Details Open-source (xmlc.enhydra.org) Uses W3C DOM APIs Generates "set" methods per tag –Source: Hello –Code: obj.setElementTitle("Goodbye") –Output: Goodbye Allows graphic designers and database programmers to develop in parallel Works with XML source too

30. XML and Java in 2001 Many apps' config files are in XML –Ant –Tomcat –Servlets Several XML-based Sun APIs –JAXP –JAXM –ebXML –SOAP (half-heartedly supported )

31. Java XML Documentation Jdox –Javadoc -> single XML file –http://www.componentregistry.com/ –Ready for transformation (e.g. XSL) Java Doclet –http://www.sun.com/xml/developers/doclet –Javadoc -> multiple XML files (one per class) Cocoon –Has alpha XML doclet

32. Soapbox: DTDs are irrelevant DTDs describe structure of an unknown document But in most applications, you already know the structure – it's implicit in the code If the document does not conform, there will be a runtime error, and/or corrupt/null data This is as it should be! GIGO. You could have a separate "sanity check" phase, but parsing with validation "on" just slows down your app Useful for large-scale document-processing applications, but not for custom apps or transformations

33. ©1996-2000 jGuru.com XML and Server-Side Java

34. Server-Side Java-XML Architecture Many possible architectures –XML Data Source disk or database or other data feed –Java API DOM or SAX or XPath or XSL –XSL optional transformation into final HTML, or HTML snippets, or intermediate XML –Java Business Logic JavaBeans and/or EJB –Java Presentation Code Servlets and/or JSP and/or XMLC

35. Server-Side Java-XML Architecture Java UIJava Business Logic XML Processors XML Data Sources HTML JSPJavaBeans ServletEJB DOM, SAX XPath XSL Filesystem XML-savvy RDBMS XML Data Feed

36. Server-Side Architecture Notes Note that you can skip any layer, and/or call within layers –e.g. XML->XSL->DOM->JSP, or –JSP->Servlet->DOM->XML

37. Cache as Cache Can Caching is essential Whatever its advantages, XML is slow Cache results on disk and/or in memory

38. ©1996-2000 jGuru.com XML Java Object Mapping

39. XML and Object Mapping Java -> XML –Start with Java class definitions –Serialize them - write them to an XML stream –Deserialize them - read values in from previously serialized file XML -> Java –Start with XML document type –Generate Java classes that correspond to elements –Classes can read in data, and write in compatible format (shareable)

40. Java -> XML Implementations Java -> XML –BeanML –Coins / BML –Sun's XMLOutputStream/XMLInputStream –XwingML (Bluestone) –JDOM BeanMapper –Quick? –JSP (must roll your own)

41. BeanML Code (Extract) Center …

42. Coins Part of MDSAX Connect XML Elements and JavaBeans Uses Sax Parser, Docuverse DOM to convert XML into JavaBean Uses BML - (Bindings Markup Language) to define mapping of XML elements to Java Classes

43. JDOM BeanMapper Written by Alex Chaffee Default implementation outputs element- only XML, one element per property, named after property Also goes other direction (XML->Java) –Doesn't (yet) automatically build bean classes Can set mapping to other custom element names / attributes

44. XMLOutputStream/XMLInputStream From some Sun engineers –http://java.sun.com/products/jfc/tsc/articles/persistence/ May possibly become core, but unclear Serializes Java classes to and from XML Works with existing Java Serialization Not tied to a specific XML representation –You can build your own plug-in parser Theoretically, can be used for XML->Java as well

45. XMLOutputStream/XMLInputStream

47. XML -> Java Implementations XML -> Java –Java-XML Data Binding (JSR 31 / Adelard) –IBM XML Master (Xmas) –Purple Technology XDB –Breeze XML Studio (v2)

48. Adelard (Java-XML Data Binding) Java Standards Request 31 Still vapor! (?)

49. Castor Implementation of JSR 31 –http://castor.exolab.orghttp://castor.exolab.org Open-source

50. IBM XML Master ("XMas") Not vaporware - it works!!! Same idea as Java-XML Data Binding From IBM Alphaworks Two parts –builder application –visual XML editor beans

51. Brett McLaughlin's Data Binding Package See JavaWorld articles

52. Purple Technology XDB In progress (still vapor) –Currently rewriting to use JDOM –JDOMBean helps Three parts –XML utility classes –XML->Java data binding system –Caching filesystem-based XML database (with searching)

53. Conclusion Java and XML are two great tastes that taste great together

54. Resources XML Developments: –Elliot Rusty Harold: Café Con Leche - metalab.unc.edu/xml Author, XML Bible –Simon St. Laurent www.simonstl.com Author, Building XML Applications General –www.xmlinfo.com –www.oasis-open.org/cover/xml.html –www.xml.com –www.jdm.com –www.purpletech.com/xml

55. Resources: Java-XML Object Mapping JSR 31 –http://java.sun.com/aboutJava/communityprocess/j sr/jsr_031_xmld.html –http://java.sun.com/xml/docs/binding/DataBinding. html XMas –http://alphaworks.ibm.com/tech/xmas

56. Resources XSL: –James Tauber: xsl tutorial: www.xmlsoftware.com/articles/xsl-by- example.html –Michael Kay Saxon home.iclweb.com/icl2/mhkay/Saxon.html –James Clark XP Parser, XT editor, XSL Transformations W3C Spec

57. Resources: JDOM –www.jdom.org

58. Thanks To John McGann Daniel Zen David Orchard My Mom