Java 2 Platform, Enterprise Edition (J2EE), now known as Java EE or Jakarta EE, is a set of specifications for developing and deploying enterprise applications. The J2EE stack comprises a range of technologies and APIs that enable developers to create scalable, robust, and secure web-based applications.

Here’s a brief overview of the primary components and technologies in the J2EE stack:

1. Java Servlets: Server-side Java components that handle HTTP requests and produce dynamic web content.

2. JavaServer Pages (JSP): A technology that allows embedding Java directly into web pages for dynamic content generation.

3. Enterprise JavaBeans (EJB): Components that encapsulate the business logic of an application. They can be session beans, entity beans, or message-driven beans.

4. Java Message Service (JMS): API for sending and receiving messages in an enterprise.

5. Java Naming and Directory Interface (JNDI): Provides naming and directory functionality, allowing applications to locate and look up data and objects via a name.

6. Java Database Connectivity (JDBC): An API for connecting Java applications to databases.

7. Java Transaction API (JTA): Allows distributed transactions across multiple resource managers.

8. JavaMail: API for sending and receiving emails.

9. Java API for XML Parsing (JAXP): Used for parsing XML documents using DOM, SAX, or XSLT.

10. Java API for XML Web Services (JAX-WS): For creating SOAP-based web services.

11. Java API for RESTful Web Services (JAX-RS): For creating RESTful web services.

12. JavaServer Faces (JSF): A UI framework for building web applications.

13. Connectors: For connecting J2EE applications to enterprise information systems.

14. Application Server: Software that provides the runtime environment for J2EE applications, like WildFly, GlassFish, WebLogic, and WebSphere.

15. Java Authentication and Authorization Service (JAAS): Provides a way for a J2EE application to authenticate and authorize specific functionality to users.