https://bz.apache.org/bugzilla/show_bug.cgi?id=65458
Bug ID: 65458
Summary: NPE when using a lambda in Session.addMessageHandler
Product: Tomcat 8
Version: 8.5.50
Hardware: PC
OS: Mac OS X 10.1
Status: NEW
Severity: critical
Priority: P2
Component: WebSocket
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ----
This is close to 57788.
When we write that:
session.addMessageHandler( ( MessageHandler.Whole<String> ) msg -> {
...}) ;
we get a NPE:
java.lang.NullPointerException
at org.apache.tomcat.websocket.Util.getGenericType(Util.java:216)
at org.apache.tomcat.websocket.Util.getMessageType(Util.java:170)
at org.apache.tomcat.websocket.WsSession.addMessageHandler(WsSession.java:206)
OTOH, doing that :
session.addMessageHandler( new MessageHandler.Whole<String>()
{
...
});
works just fine.
I think it's because MessageHandler.Whole is an Interface, and not a class,
when in the second piece of code we have a class that get created. Of course,
there might be some Java side effect I don't know about, but at this point,
this is what I infer from the Tomcat code (org.apache.tomcat.websocket.Util):
185 private static <T> TypeResult getGenericType(Class<T> type,
Class<? extends T> clazz) {
// Look to see if this class implements the interface of interest
190 // Get all the interfaces
Type[] interfaces = clazz.getGenericInterfaces();
for (Type iface : interfaces) {
... (ignored because it's not a Parameterized type)
}
206 // Interface not found on this class. Look at the superclass.
@SuppressWarnings("unchecked")
Class<? extends T> superClazz =
(Class<? extends T>) clazz.getSuperclass();
if (superClazz == null) {
// Finished looking up the class hierarchy without finding anything
return null;
}
Here, Whole extends MessageHandler so we keep going :
215 TypeResult superClassTypeResult = getGenericType(type, superClazz);
and the recursive call do the same thing with the MessageHandler interface,
which has no parent, thus returns null :
210 if (superClazz == null) {
// Finished looking up the class hierarchy without finding anything
return null;
}
and back to the caller (the same method) on line :
216 int dimension = superClassTypeResult.getDimension();
and SNAP because superClassTypeResult is null.
Note: the pb should also occurs on 8.5.69 (same code) and I guess in TC 9 and
TC 10.
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