Question

Im writing a program that should read data from an online XML file. The computation is done by classes written in Scala, should any exception be caught, it must be thrown to a Java class that will handle the exceptions. For some reason, i get an error with the exception type. What is the right exception that should be thrown when trying to access a bad URL or any similar issue (no internet connection?). Thanks!

The main class (Scala)

object test 
{
  def main(args:Array[String])
  {
    val  x:A =  new A()
  }

}

The class that parses the XML file and tries to access the URL

import java.net.{URL, URLConnection}
import xml.{XML, Elem}
import java.lang.NullPointerException
import java.io.IOException


class XMLparser {
  @throws(classOf[Exception])
  private val connectionXMLURL = "http://www.boi.org.il/currency.xml1"
  private var urlConnection:URLConnection = null
  private var url:URL = null
  private var doc:Elem = null
  private val currencies = new java.util.LinkedHashMap[String,java.lang.Double]()

  try
  {
    url = new URL(connectionXMLURL)
    urlConnection = url.openConnection
    doc = XML.load(urlConnection.getInputStream)
  }
  catch
    {
      case ex: org.xml.sax.SAXParseException => //is caught!!! and thrown!
      {
        throw  ex
      }
      case e: IOException =>
      {
        throw e
        //add error log!!
      }

      case e: NullPointerException =>
      {
        throw e
        //add error log!!
      }
      case e: Exception =>
      {
        throw e
      }      
    }

}

The class that should catch the exception (Java)

public class A 
{
    private XMLparser x;
    public A()
    {
        try
        {
            x  = new XMLparser();
        }
        catch(org.xml.sax.SAXParseException e) //Cannot catch it!!??
        {

        }
     /*   catch (Exception e)
        {
             e.printStackTrace();
        } */
    }


}

EDIT: this is the error message i get when trying to catch the exception:

scala: warning: [options] bootstrap class path not set in conjunction with -source 1.6
scala: C:\Users\home\Dropbox\Exchange Currency\src\il\hit\currencyExchange\CurrencyExchangeGUI.java:138: error: exception SAXParseException is never thrown in body of corresponding try statement
scala:       catch (org.xml.sax.SAXParseException ex)

Answer 1

The problem is that you need to declare that your constructor method (the default one) throws a checked java exception. I saw that you already added the @throws(classOf[Exception]) annotation to your code, but it is slightly misplaced for your purposes. Check this link
https://issues.scala-lang.org/browse/SI-1420

It should look like

class XMLparser @throws(classOf[Exception]) {

      private val connectionXMLURL = "http://www.boi.org.il/currency.xml1"
      ...