Servlet:Filter

index.html
==========

<form action="servlet1">
Name:<input type="text" name="name"/><br/>
Password:<input type="password" name="password"/><br/>
 
<input type="submit" value="Submit">
 
</form>

AdminServlet.java
=================

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 AdminServlet extends HttpServlet {
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        try (PrintWriter out = response.getWriter()) {response.setContentType("text/html");
       
        out.print("welcome ADMIN");
        out.close();
        }
    }

    @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);
    }
 
}

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();
         
    String password=req.getParameter("password");
    if(password.equals("admin")){
    chain.doFilter(req, resp);//sends request to next resource
    }
    else{
    out.print("username or password error!");
    RequestDispatcher rd=req.getRequestDispatcher("index.html");
    rd.include(req, resp);
    }
         
}
    public void destroy() {}
 
}



web.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">
    <servlet>
    <servlet-name>AdminServlet</servlet-name>
    <servlet-class>AdminServlet</servlet-class>
  </servlet>
 
  <servlet-mapping>
    <servlet-name>AdminServlet</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>