click here

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.*;

public class MyFilter implements Filter{
FilterConfig config;

public void init(FilterConfig config) throws ServletException {
    this.config=config;
}

public void doFilter(ServletRequest req, ServletResponse resp,
    FilterChain chain) throws IOException, ServletException {
    
    PrintWriter out=resp.getWriter();
        
    String s=config.getInitParameter("construction");
        
    if(s.equals("yes")){
         out.print("This page is under construction");
    }
    else{
         chain.doFilter(req, resp);//sends request to next resource
    }
        
}
public void destroy() {}
}

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("
welcome to servlet
");
        
    }

}

 
    HelloServlet
    HelloServlet
  

  
    HelloServlet
    /servlet1
  
  
  
  f1
  MyFilter
  
  construction
  no
  
  
  
  f1
  /servlet1