The ServletRequest interface have many methods to handle client requests to access a servlet. It is used for access client requests in servlet. HttpServletRequest extends to ServletRequest.

Below example will help you to batter understand :

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app>
<servlet>
<servlet-name>myservlet</servlet-name>
<servlet-class>ServletDemo</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>myservlet</servlet-name>
<url-pattern>/servlet</url-pattern>
</servlet-mapping>

</web-app>

index.html

<form action="servlet" method="get">  
<input type="text" name="name"><br>  
<input type="submit" value="login">  
</form>  

ServletDemo.java

import javax.servlet.http.*;  
import javax.servlet.*;  
import java.io.*;  
public class ServletDemo extends HttpServlet{  
public void doGet(HttpServletRequest req,HttpServletResponse res)  
throws ServletException,IOException  
{  
res.setContentType("text/html");  
PrintWriter out=res.getWriter();  

String name=req.getParameter("name");
out.println("Welcome "+name);  

out.close();  
}}