What is Java Servlet API?

The Java Servlet API lets you define HTTP-specific classes. A servlet class extends the capabilities of servers that host applications that are accessed by way of a request-response programming model. Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by web servers. For instance, you might use a servlet to get the text input from an online form and print it back to the screen in an HTML page and format, or you might use a different servlet to write the data to a file or database instead. A servlet runs on the server side — without an application GUI or HTML user interface (UI) of its own. Java Servlet extensions make many web applications possible.