Java Web Services

Specifications/APIs

JAX-RPC - Specification/API for Java developers to develop SOAP based interoperable web services. This API is now obsolete

JAX-WS - Successor to JAX-RPC. It requires Java 5.0, and is not backwards-compatible to JAX-RPC

JAX-RS - Java API for RESTful web services

SAAJ - API for using SOAP envelopes with or without attachments. It operates on a lower level than JAX-RPC or JAX-WS, both of which will use SOAP envelopes based on SAAJ if needed

Implementations 
compare:http://srbtechlog.blogspot.com/2011/11/axis-vs-axis2-vs-cxf-vs-spring.html

Apache Axis/Axis2

Apache CXF

Apache SOAP

JWSDP - Sun Java Webservices Developer Pack, is an implementation of JAX-RPC, SAAJ and various other XML Java technologies. It is now deprecated in favor of the Metro stack.

Metro - Web services stack used in GlassFish?. It supports SAAJ, JAX-WS, WS-Security and other standards.

Jersey - Jersey is the reference implementation of the JAX-RS API, as defined in the JSR-311

GlassFish - Open source reference implementation of J2EE 5 with JAX-WS

Spring Web Services