Simple Example of Filter

1. index.html
2. MyFilter.java
3.  HelloServlet.java
4. web.xml

index.html

<a href="servlet1">click here</a>

MyFilter.java

import java.io.IOException; 
import java.io.PrintWriter; 
 
import javax.servlet.*; 
 
public class MyFilter 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(); 
    out.print("filter is invoked before"); 
         
    chain.doFilter(req, resp);//sends request to next resource 
         
    out.print("filter is invoked after"); 
    } 
    public void destroy() {} 
} 

HelloServlet.java

import java.io.IOException; 
import java.io.PrintWriter; 
 
import javax.servlet.ServletException; 
import javax.servlet.http.*; 
 
public class HelloServlet extends HttpServlet { 
    public void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException { 
 
        response.setContentType("text/html"); 
        PrintWriter out = response.getWriter(); 
     
        out.print("<br>welcome to servlet<br>"); 
         
    } 
 
} 

web.xml

<web-app> 
 
<servlet> 
<servlet-name>s1</servlet-name> 
<servlet-class>HelloServlet</servlet-class> 
</servlet> 
 
<servlet-mapping> 
<servlet-name>s1</servlet-name> 
<url-pattern>/servlet1</url-pattern> 
</servlet-mapping> 
 
<filter> 
<filter-name>f1</filter-name> 
<filter-class>MyFilter</filter-class> 
</filter> 
  
<filter-mapping> 
<filter-name>f1</filter-name> 
<url-pattern>/servlet1</url-pattern> 
</filter-mapping> 
 
 
</web-app>