Servlet - FilterConfig

Last Updated : 30 Jan, 2022

An object of FilterConfig is created by the web container for each filter. It can be used to read filter init parameters. Placed in web.xml file. If the configuration information is modified from the web.xml file, we don't need to change the filter. So it is easier to manage the web application if any specific content is modified from time to time.

Methods of FilterConfig Interface

There are four methods in the FilterConfig interface.

1. String getFilterName(): Return the filter-name of this filter as defined in the deployment descriptor.

Syntax: public String getFilterName()

2. String getInitParameter(String name): Return a String containing the value of the named initialization parameter, or null if the parameter does not exist.

Syntax: public String getInitParameter(String name)

3. Enumeration getInitParameterNames(): Return the names of the filter's initialization parameter as an Enumeration of String object's or an empty Enumeration if the filter has no initialization parameters.

Syntax: public Enumeration getInitParameterNames()

4. ServletContext getServletContext(): Return a reference to the ServletContext in which caller is executing

Syntax: public ServletContext getServletContext()

Example

index.html

HTML

<html>
   <head>
       <title>TODO supply a title</title>
       <meta charset="UTF-8">
       <meta name="viewport" content="width=device-width, initial-scale=1.0">
   </head>
  
   <body>
       <h2>FilterConfig Demo</h2>
   <form action="abc" method="post">
       User name <input type="text" name="un"><br>
       Password <input type="password" name="up"><br>
       <input type="submit" value="Login"><input type="reset" value="Clear">
   </form>
   </body>
</html>

abc.java

Java

import static java.lang.System.out;

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;

public class abc extends HttpServlet {

    protected void
    processRequest(HttpServletRequest request,
                   HttpServletResponse response)
        throws ServletException, IOException
    {

        response.setContentType("text/html;charset=UTF-8");
        PrintWriter p = response.getWriter();
        p.println(
            "<font color='red'><h2>Welcome User</h2></font>");
    }

    // <editor-fold defaultstate="collapsed"
    // desc="HttpServlet methods. Click on the + sign on the
    // left to edit the code.">
    @Override
    protected void doGet(HttpServletRequest request,
                         HttpServletResponse response)
        throws ServletException, IOException
    {
        processRequest(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request,
                          HttpServletResponse response)
        throws ServletException, IOException
    {
        processRequest(request, response);
    }

    @Override
    public String getServletInfo()
    {
        return "Short description";
    }
}

filter_config_demo.java

Java

package demo;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class filter_config_demo implements Filter {

    FilterConfig fc;

    @Override
    public void init(FilterConfig filterConfig)
        throws ServletException
    {
        this.fc = filterConfig;
    }

    @Override
    public void doFilter(ServletRequest request,
                         ServletResponse response,
                         FilterChain chain)
        throws IOException, ServletException
    {
        String un, up;
        un = request.getParameter("un");
        up = request.getParameter("up");
        PrintWriter p = response.getWriter();
        System.out.println("My filter Name is "
                          + fc.getFilterName());
        if (un.equals(fc.getInitParameter("username"))
            && up.equals(
                fc.getInitParameter("userpassword")))

        {
            chain.doFilter(request, response);
        }

        else
        {
            RequestDispatcher rd
                = request.getRequestDispatcher(
                    "/index.html");
            rd.include(request, response);
            p.println("incorrect user name and password");
        }
    }

    @Override
    public void destroy()
    {
        this.fc = null;
    }
}

web.xml

XML

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.1" xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
                             http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd">

   <filter>
       <filter-name>filter1</filter-name>
       <filter-class>demo.filter_config_demo</filter-class>
       <init-param>
           <param-name>username</param-name>
           <param-value>sumit</param-value>
       </init-param>

       <init-param>
           <param-name>userpassword</param-name>
           <param-value>sumit@123</param-value>
       </init-param>
   </filter>

   <filter-mapping>
       <filter-name>filter1</filter-name>
       <servlet-name>abc</servlet-name>
   </filter-mapping>

   <servlet>
       <servlet-name>abc</servlet-name>
       <servlet-class>abc</servlet-class>
   </servlet>

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

   <session-config>
       <session-timeout>30</session-timeout>
   </session-config>

</web-app>