The Java EE 6 Tutorial, Volume I

Types Supported by JAX-WS

JAX-WS delegates the mapping of Java programming language types to and from XML definitions to JAXB. Application developers don’t need to know the details of these mappings, but they should be aware that not every class in the Java language can be used as a method parameter or return type in JAX-WS. For information on which types are supported by JAXB, see JAXB default data type bindings.