I need to develop a JCA adapter and am looking for some references. I searched on Amazon, and found only 2 JCA books and one of them has pretty bad comments. So I guess that
You can also consider Adam Bien's connectorZ.
If you want something more specific to Jboss you may consider Red Hat's Iron Jacamar, which is Jboss JCA implementation. There are releases compatible with JCA 1.0, 1.5, 1,6 and 1.7 with each one being backwards compatible. The download includes also a sample directory with 4 simple examples. Also at Iron Jacamar you can find a very interesting code generator and a plugin for eclipse, both of which are able to generate complete JCA adapter skeletons.