Scala example: loading network from a set of oobn files

[mbedward]

Hi all,

I really like code snippets and usage examples when I'm trying to learn a new API. So in case it is useful to others, here is the code for a minimal Scala app to load an object oriented network from a set of oobn files in a given working directory.

Warning: first attempt so beware of bugs.

Michael

Code: [Select]

package fdr.bn

import COM.hugin.HAPI.ClassCollection
import COM.hugin.HAPI.ClassParseListener
import COM.hugin.HAPI.Domain
import COM.hugin.HAPI.ExceptionHugin
import COM.hugin.HAPI.Node


/** Minimal test app to load an OO network. */
object TestApp extends App {

  val workingDir = "c:/michael/hugin/api-testing"
  val topClass = "model"

  OOBNLoader.load(workingDir, topClass) match {
    case Some(domain) =>
      println("loader returned a domain")
      
      // All we do in this test app is retrieve the network nodes and
      // print their names
      import scala.collection.JavaConverters._
      val nodes = domain.getNodes().asScala map (_.asInstanceOf[Node])
      nodes foreach (node => println(node.getName()))
      
      domain.delete()
      
    case None =>
      println("loader returned nothing")
  }
  
}


/**
 * Used to load a set of oobn files for an object oriented network
 * from a given working directory and create a Domain object.
 */
class OOBNLoader(dir: String) {

  val workingDir =
    if (dir.endsWith("/")) dir
    else dir + "/"

  def nameToPath(className: String) =
    workingDir + className + ".oobn"

  /**
   * Loads a network, given the name of the top class,
   * and returns an Option[Domain].
   */
  @throws(classOf[ExceptionHugin])
  def load(topClassName: String): Option[Domain] = {
    val cc = new ClassCollection
    try {
      val parseListener = new ParseListener(workingDir)

      val topFile = nameToPath(topClassName)
      cc.parseClasses(topFile, parseListener)
      val top = cc.getClassByName(topClassName)

      if (top == null) {
        println("Class not found: " + topClassName)
        None
      } else {
        Some(top.createDomain())
      }

    } finally {
      cc.delete()
    }
  }

  /**
   * In the Hugin Java API, a ClassParseListener is responsible for
   * loading a given network class. This implementation takes an
   * argument for the working directory which is assumed to contain
   * all of the class files (.oobn) associated with a network.
   */
  class ParseListener(dir: String) extends ClassParseListener {

    def parseError(line: Int, msg: String) {
      println("Parse error in line " + line + ": " + msg);
    }

    def insertClass(className: String, cc: ClassCollection) {
      try {
        cc.parseClasses(nameToPath(className), this);
      } catch {
        case e: Exception =>
          println("Parsing failed: " + e.getMessage());
      }
    }
  }
}

/**
 * Companion object with convenience methods.
 */
object OOBNLoader {
  /** Creates a loader for a given working directory. */
  def apply(dir: String) = new OOBNLoader(dir)
  
  /** Loads a network given a working directory and top class name. */
  def load(dir: String, topClass: String): Option[Domain] =
    OOBNLoader(dir).load(topClass)
}