why does XmlSlurper throw NumberFormatException? - grails

Question

I launch my Grails 2.1.5 app from an IDE with an exception breakpoint set for NumberFormatException (meaning that the application will break whenever this exception is thrown).
If I then execute the following code from the Grails console:
import groovy.util.*
import groovyx.net.http.*
def uri = 'http://ws.audioscrobbler.com/2.0/?artist=Yelle&mbid=f43d43c8-eedf-4628-99b0-04120e7124c8&method=artist.gettopalbums&api_key=6e331f856413a5e3dfc91ec41cea5415&limit=6'
XmlSlurper().parse(uri)
The exception breakpoint is triggered because of the following code in Long.parseLong
public static long parseLong(String s, int radix)
throws NumberFormatException
{
if (s == null) {
throw new NumberFormatException("null");
}
// rest of method omitted
}
However it seems that XmlSlurper().parse(uri) returns the expected value, so I guess this exception is handled somewhere, but I can't figure out where. I'm puzzled about why Long.parseLong is called with a null value for the first param. Is this a bug in XmlSlurper or just some strange implementation detail?
Update
As requested, here's the call stack. I'm using JDK 7 and Groovy 1.8.8. I tried debugging it myself, but as you can see, I'm missing a lot of the relevant source files.
at java.lang.Long.parseLong(Long.java:404)
at java.lang.Long.parseLong(Long.java:483)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1571)
at org.apache.xerces.impl.XMLEntityManager.setupCurrentEntity(Unknown Source:-1)
at org.apache.xerces.impl.XMLVersionDetector.determineDocVersion(Unknown Source:-1)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source:-1)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source:-1)
at org.apache.xerces.parsers.XMLParser.parse(Unknown Source:-1)
at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source:-1)
at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source:-1)
at groovy.util.XmlSlurper.parse(XmlSlurper.java:146)
at groovy.util.XmlSlurper.parse(XmlSlurper.java:212)

Answer 1

As far as I can tell, this file from the OpenJDK mercurial repository is the version of sun.net.www.protocol.http.HttpURLConnection that is in Java 7 update 25, and the relevant extract is
1570 try {
1571 cl = Long.parseLong(responses.findValue("content-length"));
1572 } catch (Exception exc) { };
so the NumberFormatException will be thrown (and immediately ignored) whenever an HTTP response doesn't have a Content-Length header.