How to parse xml into "messages" and print them in scala using flow analysis?

Question

How to parse xml into "messages" and print them in scala using flow analysis?

Now that I know how to parse xml in scala as a stream, I need help understanding a non-trivial example.

I would like to parse the following xml as a stream and send a message (print to the console for this example) whenever I parse the full message.

I understand that scala thread-based parsing uses case classes to handle different elements, but I'm just getting started, and I don't quite understand how to do this.

This works for me in java using the stax parser, and I'm trying to translate it into scala.

Any help would be greatly appreciated.

<?xml version="1.0" ?>
<messages>
<message>
   <to>john.doe@gmail.com</to>
   <from>jane.doe@gmail.com</from>
   <subject>Hi Nice</subject>
   <body>Hello this is a truly nice message!</body>
</message>
<message>
   <to>joe@gmail.com</to>
   <from>jane.doe@gmail.com</from>
   <subject>Hi Nice</subject>
   <body>Hello this is a truly nice message!</body>
</message>
</messages>

+3

xml scala

Scarcher2 May 28 '10 at 13:56

1

huynhjl · Accepted Answer · 2010-05-28T15:07:21+0000

2.8.

. (, , ):

import scala.xml.pull._
import scala.io.Source
import scala.collection.mutable.Stack

val src = Source.fromString(xml)
val er = new XMLEventReader(src)
val stack = Stack[XMLEvent]()
def iprintln(s:String) = println((" " * stack.size) + s.trim)
while (er.hasNext) {
  er.next match {
    case x @ EvElemStart(_, label, _, _) =>
      stack push x
      iprintln("got <" + label + " ...>")
    case EvElemEnd(_, label) => 
      iprintln("got </" + label + ">")
      stack pop;
    case EvText(text) => 
      iprintln(text) 
    case EvEntityRef(entity) => 
      iprintln(entity) 
    case _ => // ignore everything else
  }
}

- , , , .

, EvElemStart(pre, label, attrs, scope) , if .

, 2.7.x, , http://lampsvn.epfl.ch/trac/scala/ticket/2583, .

, ( Scala):

class Message() {
  var to:String = _
  var from:String = _
  override def toString(): String = 
    "from %s to %s".format(from, to)
}

var message:Message = _
var sb:StringBuilder = _

while (er.hasNext) {
  er.next match {
    case x @ EvElemStart(_, "message", _, _) =>
      message = new Message
    case x @ EvElemStart(_, label, _, _) if
        List("to", "from") contains label =>
      sb = new StringBuilder 
    case EvElemEnd(_, "to") => 
      message.to = sb.toString
    case EvElemEnd(_, "from") => 
      message.from = sb.toString
      sb = new StringBuilder 
    case EvElemEnd(_, "message") => 
      println(message)
    case EvText(text) if sb != null => 
      sb ++= text
    case EvEntityRef(entity) => 
      sb ++= unquote(entity) // todo
    case _ => // ignore everything else
  }
}

How to parse xml into "messages" and print them in scala using flow analysis?

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