Java FilterConfig interface

FilterConfig object is created and used by the web container to pass init parameters to a filter during initialization.

Methods of FilterConfig interface:

1. getFilterName(): Returns the name of the filter defined in web.xml.

Syntax:

public String getFilterName()

2. getInitParameter(String name): Returns the value of the specified parameter.

Syntax:

 public String getInitParameter(String name)

3. getInitParameterNames(): Returns the names of all parameters as Enumeration.

Syntax:

public Enumeration getInitParameterNames()

4. getServletContext(): Returns the object of ServletContext.

Syntax:

 public ServletContext getServletContext()

Example:

MyFilter.java

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

/**
* This class is used as a filter.
* @author W3schools360
*/
public class MyFilter implements Filter {
	private static final long serialVersionUID = 1L;
	private FilterConfig filterConfig;
	
	public void init(FilterConfig filterConfig) 
	                         throws ServletException {
		this.filterConfig = filterConfig;
	}  
    
	public void doFilter(ServletRequest request, 
			ServletResponse response,FilterChain chain) 
	                   throws IOException, ServletException {
		
	          
	response.setContentType("text/html"); 
    	PrintWriter out = response.getWriter();
    	
    	//get parameters from filterConfig object.
    	String appUser = filterConfig.getInitParameter("appUser");  
    	if(appUser.equals("jai")){
    		chain.doFilter(request, response);
    	}
    	else {
    		out.print("Invalid application user.");
    	}	          
    }  
	
    public void destroy() {
    	
    }  
}

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;

/**
 * This class is used to print login 
 * message if user logged in successfully.
 */
public class WelcomeServlet extends HttpServlet {
   private static final long serialVersionUID = 1L;
       
   //no-argument constructor
    public WelcomeServlet() {
       
    }

    protected void doGet(HttpServletRequest request, 
            HttpServletResponse response)
                   throws ServletException, IOException {
        response.setContentType("text/html");  
        PrintWriter out = response.getWriter();  
          
        out.print("<h1>Valid application user.</h1>");  
        out.close();  
    }
}

web.xml

<!--?xml version="1.0" encoding="UTF-8"?-->
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemalocation="http://java.sun.com/xml/ns/javaee 
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  
  <servlet>
    <servlet-name>WelcomeServlet</servlet-name>
    <servlet-class>
        com.w3schools.business.WelcomeServlet
    </servlet-class>
  </servlet>
  
  <servlet-mapping>
    <servlet-name>WelcomeServlet</servlet-name>
    <url-pattern>/WelcomeServlet</url-pattern>
  </servlet-mapping>
  
  <filter>  
      <filter-name>MyFilter</filter-name>  
      <filter-class>
          com.w3schools.business.MyFilter
      </filter-class> 
      <init-param>
        <param-name>appUser</param-name>
        <param-value>jai</param-value>
      </init-param> 
  </filter>  
  
  <filter-mapping>  
      <filter-name>MyFilter</filter-name>  
      <url-pattern>/WelcomeServlet</url-pattern>  
  </filter-mapping>  
  
</web-app>