In Filter, we can perform authentication also. Let’s see the following example, here, we are checking password given by the user in filter class, if given password is ABC, it will forward the request to the Welcome servlet otherwise it will display error message.

Example of authentication using filter

Required Files:

1. index.html
2. MyFilter1.java
3. WelcomeServlet.java
4. web.xml

index.html

<form action="WelcomeServlet">
    Name:<input type="text"
    name="name"><br/>

    Password:<input type="password" 
    name="pwd"><br/>

    <input type="submit" value="login">

</form>

MyFilter1.java

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.*;
public class MyFilter1 implements Filter{

    public void init(FilterConfig arg0) throws ServletException {}

        public void doFilter(ServletRequest request, ServletResponse response, 
        FilterChain chain) throws IOException, ServletException {

            PrintWriter out=response.getWriter();
            String  s = request.getParameter("pwd");
            if(s.equals("ABC")){

                chain.doFilter(request, response);//sends request to next resource 
            }
            else{
                out.print("Invalid  username or password");
                RequestDispatcher rd=request.getRequestDispatcher("index.html");
                rd.include(request, response); 
            }

        }
    public void destroy() {}
}

WelcomeServlet.java

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.*;

publi class WelcomeServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.print("welcome JavaRace");
        out.close();
    } 

}

web.xml

<web-app>
    <servlet>
        servlet-name>WelcomeServlet</servlet-name>
        <servlet-class>WelcomeServlet</servlet-class>
    </servlet>

    <servlet-mapping> 
        <servlet-name>WelcomeServlet</servlet-name>
        <url-pattern>/WelcomeServlet</url-pattern>
    </servlet-mapping>

    <filter>
        <filter-name>f1</filter-name>
        <filter-class>MyFilter1</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>f1</filter-name>
        <url-pattern>/WelcomeServlet</url-pattern>
    </filter-mapping>

</web-app>