Scala, XML and GAE

scala, xml and gae
mark@ryall.name

val document =
<root>
<child>
<grandchild an_attribute=quot;value1quot; />
<grandchild an_attribute=quot;value2quot; />
</child>
</root>

val document =
scala.xml.Elem(null, quot;rootquot;, scala.xml.Null, scala.xml.TopScope,
scala.xml.Elem(null, quot;childquot;, scala.xml.Null, scala.xml.TopScope,
scala.xml.Elem(null, quot;grandchildquot;,
new scala.xml.UnprefixedAttribute(quot;an_attributequot;,quot;value1quot;, scala.xml.Null),
scala.xml.TopScope,
scala.xml.Text(quot;content1quot;)
),
scala.xml.Elem(null, quot;grandchildquot;,
new scala.xml.UnprefixedAttribute(quot;an_attributequot;,quot;value2quot;, scala.xml.Null),
scala.xml.TopScope,
scala.xml.Text(quot;content2quot;)
)
)
)

// immediate descendant of document called 'child'
document quot;childquot;

// any descendant of document called 'another_grandchild'
document quot;another_grandchildquot;

// any descendant attribute called 'an_attribute'
document quot;@an_attributequot;

• match single node with {variable}
• match node sequence with {variable @ _*}
• cannot match attribute directly

val a = document match {
case Elem(_, quot;rootquot;, _, _, _*) => 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> =>
case <grandchild>{contents @ _*}</grandchild> =>
case _ => println(quot;leafquot;)
}
}

Concatenation

def add(p: Node, newEntry: Node ): Node =
p match {
case <div>{ ch @ _* }</div> =>
<div>{ ch }{ newEntry }</div>
}

Extracting attributes

document match {
case n @ <grandchild>{ _* }</grandchild> =>
println(n.attribute(quot;an_attributequot;))
}

scala.xml.XML.saveFull(quot;filename.xmlquot;, document,
quot;UTF-8quot;, true, null)

val document2 = scala.xml.XML.loadFile(quot;filename.xmlquot;)

val src =
scala.io.Source.fromString(quot;<root><child></child></root>quot;)
val er = new scala.xml.pull.XMLEventReader().initialize(src)
er.next
...

var variable1 = quot;value1quot;

val variable2 = <another_grandchild an_attribute=quot;value2quot; />

var document =
<root>
<child>
<grandchild an_attribute={variable1} />
{variable2}
</child>
</root>

• ‘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/

class Servlet extends HttpServlet {
override def doGet(request: HttpServletRequest, response: HttpServletResponse):
Unit = {
val out = response.getWriter()
...
out.println(<html>{head}<body>{body}</body></html>)
}
}

var userService = UserServiceFactory.getUserService();
var user = userService.getCurrentUser();

if (user == null) {
response.sendRedirect(userService.createLoginURL(request.getRequestURI()))
return
}

@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
}

Scala, XML and GAE

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