Using WebSockets with EJB 3 - EJB 3 in Action - page 588

Table 14.1. @OnMessage parameter types

Type Parameter type Partial message Notes

Text String No

Text int, long, float, double, etc. No

If boolean true, message fin-
ished.

Text String, boolean Yes

Decoder.Text must be re-
gistered.

Text Custom object No

Binary byte[] No

If boolean true, message fin-
ished.

Binary byte[], boolean Yes

Binary ByteBuffer No

If boolean true, message fin-
ished.

Binary ByteBuffer, boolean Yes

Binary InputStream Yes

Decover.Binary must be re-
gistered.

Binary Custom object No

Pong PongMessage No

With the custom object types in table 14.1 , custom decoders must be registered on the
@ServerEndpoint . In addition to the parameters listed in the table, a message annot-
ated with @OnMessage can accept the following parameters:

• Session— Session object associated with the client
• @PathParam— Maps URI variables to parameters

The parameters may appear in any order—the container will dynamically invoke the meth-
od using reflection.

Unlike the MessageHandler interface you saw earlier, methods decorated with
@OnMessage can return data. If the return type is something other than a String or a
Java primitive, an encoder must be registered on @ServerEndpoint for the type; other-
wise an error will be generated.

Now that you have a theoretical handle on this annotation, let's look at an example of it
from ActionBazaar in the next listing.