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
<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 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 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
<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>
Output:
Click on the login button, if the password is correct then the above message will be shown to the user.
