What is Servlets in Java ?

Servlets are a fundamental technology for building web applications in Java. They are Java classes that run on a web server and handle HTTP requests and responses, making it possible to build dynamic, interactive websites.

A servlet is a small Java program that runs within a web server, responding to HTTP requests from clients. When a client sends a request to a web server, the servlet is responsible for processing the request, generating the appropriate response, and sending it back to the client.

To write a servlet in Java, you need to extend the javax.servlet.http.HttpServlet class and override the doGet or doPost methods. These methods are called by the web server whenever an HTTP GET or POST request is received.

Here's an example of a simple servlet that generates a response with a message:

In this example, the servlet extends the HttpServlet class and overrides the doGet method. The doGet method generates an HTML response with a message, "Hello, World!", and sets the content type of the response to "text/html".

To run a servlet, you need to deploy it on a web server. There are many web servers available that support servlets, including Apache Tomcat, Jetty, and GlassFish. To deploy a servlet on a web server, you need to create a web.xml file that defines the servlet and maps it to a URL.

Here's an example of a web.xml file for the HelloWorldServlet:

In this example, the web.xml file defines a servlet named "HelloWorldServlet" and maps it to the URL "/hello".

Servlets are a powerful and flexible technology for building web applications in Java. They are widely used for building dynamic, interactive websites and for building RESTful APIs. Whether you are building a simple website or a complex web application, servlets are an excellent choice for building the back-end logic of your web application.