Web Services:

Веб сервисы = Веб службы. Я постараюсь называть их везде Веб сервисами. Так проще.
Веб сервисы - приложения просто обмениваются между собой XML данными по сети. Как следствие, зависимотей к определенному языку или пратформе не существует.

Выделяют чаще всего:

• SOAP Web Services with JAX-WS
• RESTful Web Services with JAX-RS

Simple Object Access Protocol (SOAP)
Representational State Transfer protocol (REST)

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When using the SOAP protocol, web service operations are defined in an XML document called a Web Services Definition Language (WSDL) file. After creating the WSDL, implementation of web services is done in a proper programming language such as Java.
Representational State Transfer (REST) is an architectural style in which web services are viewed as resources and can be identified by Uniform Resource Identifiers (URIs).

Restful

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Restful:

• Glassfish - Jersey (Sun, Oracle)
• JBoss - RESTEasy (RedHat)

Restful примеры:

• Overview of JAX-RS 1.0 Features (Jersey)
• Integrating JBoss RESTEasy and Spring MVC

Книги:

• Restful Java Web Services (frameworks Jersey's JAX-RS, Restlet's Lightweight REST, JBoss's JAX-RS RESTEasy, and Struts 2 with the REST plugin.)