AsyncWikiErrorHandling.scala

import java.net.URL
import java.util.Scanner

import rx.lang.scala.Observable

object AsyncWikiErrorHandling extends App {
  /*
   * Fetch a list of Wikipedia articles asynchronously, with error handling.
   */
  def fetchWikipediaArticleAsynchronously(wikipediaArticleNames: String*): Observable[String] = {
    Observable(subscriber => {
      new Thread(new Runnable() {
        def run(): Unit = {
          try {
            for (articleName <- wikipediaArticleNames) {
              if (subscriber.isUnsubscribed) {
                return
              }
              val url = "http://en.wikipedia.org/wiki/" + articleName
              val art = new Scanner(new URL(url).openStream()).useDelimiter("\\A").next()
              subscriber.onNext(art)
            }
            if (!subscriber.isUnsubscribed) {
              subscriber.onCompleted()
            }
          } catch {
            case t: Throwable => subscriber.onError(t)
          }
        }
      }).start()
    })
  }

  fetchWikipediaArticleAsynchronously("Tiger", "Elephant")
    .subscribe(
      art => println("--- Article ---\n" + art.substring(0, 125)),
      e => println("--- Error ---\n" + e.getMessage) )
}