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 “neveropen”, 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 classesimport java.io.IOException;import java.io.PrintWriter;import javax.servlet.*; // Class// Implementing Filter classpublic 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("neveropen")) { // 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 classesimport 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 classpublic 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> |
Output:
Click on the login button, if the password is correct then the above message will be shown to the user.
