Scala, XML and GAE
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scala, xml and gae [email protected]
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Presentation at first Melbourne Scala User Group 27th April, 2009
Transcript of Scala, XML and GAE
xml literals
val document =<root> <child> <grandchild an_attribute="value1" /> <grandchild an_attribute="value2" /> </child></root>
val document =scala.xml.Elem(null, "root", scala.xml.Null, scala.xml.TopScope, scala.xml.Elem(null, "child", scala.xml.Null, scala.xml.TopScope, scala.xml.Elem(null, "grandchild", new scala.xml.UnprefixedAttribute("an_attribute","value1", scala.xml.Null), scala.xml.TopScope, scala.xml.Text("content1") ), scala.xml.Elem(null, "grandchild", new scala.xml.UnprefixedAttribute("an_attribute","value2", scala.xml.Null), scala.xml.TopScope, scala.xml.Text("content2") ) ))
extraction operators
// immediate descendant of document called 'child'document \ "child"
// any descendant of document called 'another_grandchild'document \\ "another_grandchild"
// any descendant attribute called 'an_attribute'document \\ "@an_attribute"
pattern matching
• match single node with {variable}
• match node sequence with {variable @ _*}
• cannot match attribute directly
val a = document match { case Elem(_, "root", _, _, _*) => true case _ => null}
val a = document match { case <root>{ _* }</root> => true case _ => false}
def process(node: scala.xml.Node): Unit = { println(node) node match { case <root>{contents @ _* }</root> => for (a <- contents) process(a) case <child>{contents @ _*}</child> => for (a <- contents) process(a) case <grandchild>{contents @ _*}</grandchild> => for (a <- contents) process(a) case _ => println("leaf") }}
def add(p: Node, newEntry: Node ): Node = p match { case <div>{ ch @ _* }</div> => <div>{ ch }{ newEntry }</div> }
Concatenation
document match { case n @ <grandchild>{ _* }</grandchild> => println(n.attribute("an_attribute"))}
Extracting attributes
persisting and restoring
scala.xml.XML.saveFull("filename.xml", document, "UTF-8", true, null)
val document2 = scala.xml.XML.loadFile("filename.xml")
stream parsing
val src = scala.io.Source.fromString("<root><child></child></root>")val er = new scala.xml.pull.XMLEventReader().initialize(src)er.next...
building xml
var variable1 = "value1"
val variable2 = <another_grandchild an_attribute="value2" />
var document = <root> <child> <grandchild an_attribute={variable1} /> {variable2} </child> </root>
google app engine
• ‘cloud’ web hosting environment on google’s infrastructure
• uses non relational ‘bigtable’ for data persistance
• user authentication uses google accounts or openid
• also has email (sending), memcache and image manipulation services
• working example:
• code: http://bitbucket.org/markryall/scalagae
• live: http://pairs.appspot.com
• use latest datanucleus enhancer from http://www.datanucleus.org/downloads/maven2-nightly/org/datanucleus/datanucleus-enhancer/1.1.2/
basics
class Servlet extends HttpServlet { override def doGet(request: HttpServletRequest, response: HttpServletResponse): Unit = { val out = response.getWriter()... out.println(<html>{head}<body>{body}</body></html>) }}
authentication
var userService = UserServiceFactory.getUserService();var user = userService.getCurrentUser();
if (user == null) { response.sendRedirect(userService.createLoginURL(request.getRequestURI())) return}
persistence
@PersistenceCapable {val identityType = IdentityType.APPLICATION}class Person(@Persistent var firstName: String,@Persistent var lastName: String) { @PrimaryKey @Persistent {val valueStrategy = IdGeneratorStrategy.IDENTITY} var id: java.lang.Long = null }
