Can you explain what a servlet API in Java is and how it is used?

The Servlet API in Java is a set of classes and interfaces provided by the javax.servlet and javax.servlet.http packages that allow creating web applications on the server side.

Servlets handle HTTP requests and generate HTTP responses. The main class is HttpServlet, from which user-defined servlets inherit. In it, methods like doGet(), doPost(), and others are overridden to handle respective HTTP methods.

Example of a simple servlet:

public class HelloServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<h1>Hello, Servlet!</h1>");
    }
}

The Servlet API is used in Java EE and Jakarta EE to create dynamic web pages, handle forms, manage sessions, etc.