Servlet

• is a Java API running on the server machine which can intercept the requests made by the client and can generate/send a response accordingly

• In order to run Servlets, you need a servlet container

Servlet API/Specification

see: Java - Servlet API/Specification (2.5 - 3.0 - 3.1 - 4.0 - 5.0)

Servlet Containers

There are several servlet containers:

• Apache Tomcat
• Eclipse Jetty
• JBoss Undertow
• WebLogic
• GlassFish
• WebSphere

Which Java Application Server Should I Use?

Application Servers

There are also Java EE application servers which in turn also contain a servlet container besides other Java EE APIs such as JSF, JPA, EJB, etc. See also What exactly is Java EE?

• JBoss WildFly
• Apache TomEE
• IBM WebSphere Liberty
• Payara
• Eclipse GlassFish

Resources

• https://stackoverflow.com/tags/servlets/info