Servlet is a Java application programming interface (API) running on the server machine which can intercept the requests made by the client and can generate/send a response accordingly

Specifications

• Jakarta EE 9: Jakarta Servlet 5.0 Specification
• Jakarta EE 8: Jakarta Servlet 4.0 Specification
• Java EE 8: Java Servlet 4.0 Specification (JSR 369)
• Java EE 7: Java Servlet 3.1 Specification (JSR 340)
• Java EE 6: Java Servlet 3.0 Specification (JSR 315)
• Java EE 5: Java Servlet 2.5 Specification (JSR 154)

Specifications - Differences

• StackOverflow - 2.5 vs 3.0

Servlet Containers

see: Specification - Servlet Containers - Application Servers

Servlet API

• Java - Servlet (HttpServlet - DispatcherServlet)
• Java - Servlet Filters

Resources

• https://docs.oracle.com/javaee/6/tutorial/doc/bnafd.html
• https://stackoverflow.com/tags/servlets/info