There are several plugins and projects that are relevant for developers that use Oracle Application Server or Oracle Database server and Eclipse as there favorite IDE.

Oracle Database

• The Oracle database plugin for Eclipse extends the Eclipse data tool platform. It's now possible to browse Oracle database's objects within Eclipse.
  

Oracle Application Server

• Eclipse Web tools project has support for deployment to OC4J. See for a (slightly old) article: Eclipse website
• Eclipse Dali project supports mapping Java objects to relational tables using any JPA compliant runtime (TopLink/Eclipse Link, KODO or Hibernate for example).