Servlet API

Servlets are the Java programs that run on the Java-enabled web server or application server. They are used to handle the request obtained from the webserver, process the request, produce the response, then send a response back to the webserver. In Java, to create web applications we use Servlets. To create Java Servlets, we need to use Servlet API which contains all the necessary interfaces and classes. Servlet API has 2 packages namely,

• javax.servlet
• javax.servlet.http

javax.servlet

• This package provides the number of interfaces and classes to support Generic servlet which is protocol independent.
• These interfaces and classes describe and define the contracts between a servlet class and the runtime environment provided by a servlet container.

Classes available in javax.servlet package: 

Interfaces available in javax.servlet package: 

Exceptions in javax.servlet package: 

javax.servlet.http

• This package provides the number of interfaces and classes to support HTTP servlet which is HTTP protocol dependent.
• These interfaces and classes describe and define the contracts between a servlet class running under HTTP protocol and the runtime environment provided by a servlet container.

Classes available in javax.servlet.http package: 

Interfaces available in javax.servlet.http package: 

GenericServlet Class

Servlet API provide GenericServlet class in javax.servlet package.

public abstract class GenericServlet
extends java.lang.Object
implements Servlet, ServletConfig, java.io.Serializable

• An abstract class that implements most of the servlet basic methods.
• Implements the Servlet, ServletConfig, and Serializable interfaces.
• Protocol-independent servlet.

• Makes writing servlets easier by providing simple versions of the lifecycle methods init() and destroy().
• To write a generic servlet, you need to extend javax.servlet.GenericServlet class and need to override the abstract service() method.

HttpServlet Class

Servlet API provides HttpServlet class in javax.servlet.http package.

public abstract class HttpServlet
extends GenericServlet
implements java.io.Serializable

• An abstract class to be subclassed to create an HTTP-specific servlet that is suitable for a Web site/Web application.
• Extends Generic Servlet class and implements Serializable interface.
• HTTP Protocol-dependent servlet.

To write a Http servlet, you need to extend javax.servlet.http.HttpServlet class and must override at least one of the below methods,

• doGet() - to support HTTP GET requests by the servlet.
• doPost() - to support HTTP POST requests by the servlet.
• doPut() - to support HTTP PUT requests by the servlet.
• doDelete() - to support HTTP DELETE requests by the servlet.
• init() and destroy() - to manage resources held in the life of the servlet.
• getServletInfo() - To provide information about the servlet itself like the author of servlet or version of it etc.

Servlet API Package Hierarchy

Below is the package hierarchy of Generic Servlet and HTTP Servlet.

Servlet API provides all the required interfaces, classes, and methods to develop a web application. we need to add the servlet-api.jar file in our web application to use the servlet functionality. We can download this jar file from Maven Repository.