Metro is an opensource web service stack that is a part of the GlassFish project, though it can also be used in a stand-alone configuration. Components of metro include JAXB RI, JAX-WS RI, SAAJ RI, StAX (SJSXP implementation) and WSIT. It is available under the CDDL and GPLv2 (with classpath exception.)
Originally, the Glassfish project developed two semi-independent projects :
- JAX-WS RI, the Reference implementation of the JAX-WS specification
- WSIT, a Java implementation of some of the WS-* and an enhanced support for interoperability with the .NET Framework. It is based on JAX-WS RI as "Web Service layer".
In June 2007, it has been decided to bundle these two components as a single component named Metro.
Metro is bundled with numerous Application Servers  such as :
- Sun Java System Application Server Platform Edition 9.x
- Oracle WebLogic Server
- JBoss (version 5.x only)
- TmaxSoft JEUS 6.x
Metro compares well with other web service frameworks in terms of functionality. A comparison is provided by Codehaus at , which compares Apache Axis 1.x, Axis 2.x, Celtix, Glue, JBossWS, Xfire 1.2 and JAX-WS RI + WSIT (the bundle was not yet named Metro at this time).