Servlet Filters

package com.example.filters;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.*;
import java.io.*;

// Apply to all URLs
@WebFilter("/*")
public class LoggingFilter implements Filter {

    private FilterConfig filterConfig;

    // Called once when filter is initialized
    @Override
    public void init(FilterConfig config) throws ServletException {
        this.filterConfig = config;
        System.out.println("LoggingFilter initialized");
    }

    // Called for every request matching the URL pattern
    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
                         FilterChain chain) throws IOException, ServletException {

        HttpServletRequest  req  = (HttpServletRequest)  request;
        HttpServletResponse resp = (HttpServletResponse) response;

        long startTime = System.currentTimeMillis();
        String uri     = req.getRequestURI();
        String method  = req.getMethod();
        String ip      = req.getRemoteAddr();

        System.out.println("[REQUEST] " + method + " " + uri + " from " + ip);

        // Pass request to next filter or servlet
        chain.doFilter(request, response);

        // Post-processing (after servlet response)
        long duration = System.currentTimeMillis() - startTime;
        int status = resp.getStatus();
        System.out.println("[RESPONSE] " + method + " " + uri
                + " -> " + status + " (" + duration + "ms)");
    }

    // Called once when filter is destroyed
    @Override
    public void destroy() {
        System.out.println("LoggingFilter destroyed");
    }
}

// Protect /admin/* URLs
@WebFilter("/admin/*")
public class AuthFilter implements Filter {

    private static final String[] PUBLIC_PATHS = {"/login", "/register", "/public"};

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
                         FilterChain chain) throws IOException, ServletException {

        HttpServletRequest  req  = (HttpServletRequest)  request;
        HttpServletResponse resp = (HttpServletResponse) response;

        String path = req.getRequestURI().substring(req.getContextPath().length());

        // Check if path is public
        for (String publicPath : PUBLIC_PATHS) {
            if (path.startsWith(publicPath)) {
                chain.doFilter(request, response); // Allow through
                return;
            }
        }

        // Check if user is logged in
        HttpSession session = req.getSession(false);
        boolean loggedIn = (session != null && session.getAttribute("username") != null);

        if (loggedIn) {
            chain.doFilter(request, response); // Allow through
        } else {
            // Redirect to login
            resp.sendRedirect(req.getContextPath() + "/login?redirect=" + path);
        }
    }

    @Override public void init(FilterConfig config) {}
    @Override public void destroy() {}
}