The J2EE Server Tools providing a comfortable way to integrate the Java EE Servers (e.g. GlassFish) into the Eclipse IDE. For the latest release of Eclipse (4.2 - Juno) the integration is a little bit tricky.
First you need to instal the JST plugin via menu "Help>install new Software" and search for "server". Select the "JST Server Adapters" and install it.
Next you need to add a extra update site to install the latest GlassFish adapters. Add the followin Update Site URL:
Read also the following blog from Vince Kreamer for deails: