Servlet – Authentication Filter

Last Updated : 16 Feb, 2022

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.

Authentication Filter In Servlets

Authentication may be done in the filter. Here, we’ll verify the user’s password in the ServletFilter class; if the password is “geeksforgeeks”, the request will be sent to the Gfg servlet; otherwise, an error message will be displayed.

Implementation: Let’s look at a simple example of utilizing a filter to authenticate a user. We’ve produced four files here:

index.html
Gfg.java
ServletFilter.java
web.xml

File: index.html

HTML

<form action = "servlet1"> 
  
               Name: < input type = "text" name = "name" / > < br / > < br / > 
  
                                    Password: < input type = "password" name = "password" / > < br / > < br / > 
  
                                            <input type = "submit" value = "login"> 
  
                                                    < / form >

Example 1-A:

Java

// Java Program to Illustrate ServletFilter Class 
  
// Importing required classes 
import java.io.IOException; 
import java.io.PrintWriter; 
import javax.servlet.*; 
  
// Class 
// Implementing Filter class 
public class ServletFilter implements Filter { 
  
    public void init(FilterConfig arg0) 
        throws ServletException 
    { 
    } 
  
    public void doFilter(ServletRequest req, 
                         ServletResponse resp, 
                         FilterChain chain) 
        throws IOException, ServletException 
    { 
  
        PrintWriter out = resp.getWriter(); 
  
        String password = req.getParameter("password"); 
  
        if (password.equals("geeksforgeeks")) { 
  
            // Sending request to next 
            chain.doFilter(req, resp); 
        } 
  
        // Password incorrect 
        else { 
            out.print("username or password is wrong"); 
            RequestDispatcher rd 
                = req.getRequestDispatcher("index.html"); 
            rd.include(req, resp); 
        } 
    } 
    public void destroy() {} 
}

Example 1-B:

Java

// Java Program to Illustrate GFG Class 
  
// Importing required classes 
import java.io.IOException; 
import java.io.PrintWriter; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
  
// Class 
// Derived from HttpServlet class 
public class GFG extends HttpServlet { 
  
    // Getting request response 
    public void doGet(HttpServletRequest request, 
                      HttpServletResponse response) 
        throws ServletException, IOException 
    { 
  
        response.setContentType("text/html"); 
        PrintWriter out = response.getWriter(); 
  
        out.print("welcome to GEEKSFORGEEKS"); 
  
        // Closing connections to 
        // avoid any memory leakage 
        out.close(); 
    } 
}

File: web.xml

XML

<web-app>   
 <servlet>   
    <servlet-name>Gfg</servlet-name>   
    <servlet-class>Gfg</servlet-class>   
  </servlet>   
    
  <servlet-mapping>   
    <servlet-name>Gfg</servlet-name>   
    <url-pattern>/servlet1</url-pattern>   
  </servlet-mapping>   
      
 <filter>   
  <filter-name>f1</filter-name>   
  <filter-class>ServletFilter</filter-class>   
  </filter>   
  <filter-mapping>   
  <filter-name>f1</filter-name>   
  <url-pattern>/servlet1</url-pattern>   
  </filter-mapping>   
      
</web-app>