Exceptions and XMPP Errors

There is one abstract XmppException for most kind of exceptions, which are related to XMPP.

Mainly, there are three subclasses of it:

  • StreamErrorException for Stream Errors.
  • StanzaException for Stanza Errors.
  • NoResponseException for IQ queries, which didn't receive a response.

Dealing with Stream Errors

XMPP Stream Errors are unrecoverable, which means the session will get disconnected after they have occurred.

Here's an example how to react to stream errors.

xmppClient.addSessionStatusListener(e -> {
    if (e.getThrowable() instanceof StreamErrorException) {
        StreamErrorException streamException = (StreamErrorException) e.getThrowable();
        if (streamException.getCondition() == Condition.SYSTEM_SHUTDOWN) {
            // Server was shut down.

Dealing with Stanza Errors and Lack of Responses

Most stanza errors are returned in response to an IQ-get or IQ-set query.

For querying another XMPP entity, there's a query method on the XmppClient class, which queries another entity for information and which is used by most methods.

Now two things can happen:

  • The entity does not respond at all.
  • The entity returned a stanza error.

In the first case a NoResponseException is thrown, in the latter case a StanzaException is thrown.

If you want to determine, which kind of exception it is, simply ask for their type.

Here's an example:

try {
    EntityTime entityTime = entityTimeManager.getEntityTime(Jid.of("juliet@example.net/balcony")).getResult();
} catch (NoResponseException e) {
    // The entity did not respond
} catch (StanzaException e) {
    if (e.getCondition() == Condition.SERVICE_UNAVAILABLE) {
        // The entity returned a <service-unavailable/> stanza error.
} catch (XmppException e) {
    // everything else

As you can see asking for the type and then for the specific condition gets you where you want.

Btw: If you wonder, why the error conditions aren't represented as enum, it is because some error conditions like <gone/> have additional data.