J2EE is a Java platform for developing enterprise web applications. It uses a 3-tier architecture with the client tier for presentation, business tier for application logic, and database tier for data persistence. Key J2EE technologies include servlets for generating dynamic web responses, JSPs for separating presentation from logic, and EJBs for encapsulating business logic. Servlets handle HTTP requests and responses, have a lifecycle of being loaded, initialized, used to service requests, and destroyed. JSPs generate dynamic content using declaration, scriptlet, expression, directive, and action tags.