Servlet Filter

WhiteList.java

package com.toowards.sbr;

import com.google.common.base.Charsets;
import com.google.common.io.Files;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.List;

/**
 * White list class
 * User: Jason@toowards
 * Date: 06/09/2013
 */
public class WhiteList {
    private static String WHITE_LIST_FILENAME;

    private List<String> whiteList;   // white list data
    private static WhiteList instance;
    private static Object lock = new Object();

    public static WhiteList getInstance() {
    	try
    	{
    		// finds resource relative to the class location
		URL url = new WhiteList().getClass().getResource("whitelist.txt");
    		WHITE_LIST_FILENAME= url.getPath();
    	}catch(Exception ioe)
    	{
    		ioe.printStackTrace();
    	}
        if (instance == null) {
            synchronized (lock) {
                if (instance == null) {
                    instance = new WhiteList();
                    File file = new File(WHITE_LIST_FILENAME);
                    try {
                        instance.whiteList = Files.readLines(file, Charsets.UTF_8);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
        return instance;
    }

    public List<String> getWhiteList() {
        return whiteList;
    }
}

WhiteListFilter

package com.toowards.sbr;

import com.google.common.io.Files;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.util.List;

/**
 * White list class
 * User: Jason@toowards
 * Date: 09/09/2013
 */
public class WhiteListFilter implements Filter {
    private static String IP = "ip";

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    /**
     * whitelist filter
     *
     * @param servletRequest
     * @param servletResponse
     * @param filterChain
     * @throws IOException
     * @throws ServletException
     */
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) servletRequest;
        HttpServletResponse resp = (HttpServletResponse) servletResponse;
        String ip = req.getRemoteAddr();
        WhiteList whiteList = WhiteList.getInstance();
        if (!whiteList.getWhiteList().contains(ip)) {  // Surely we can do preg match to validate ip based on pattern here
            resp.setCharacterEncoding("UTF-8");
            resp.getWriter().println("IP restricted");
        } else {
            resp.setCharacterEncoding("UTF-8");
            filterChain.doFilter(req, resp);
        }
    }

    @Override
    public void destroy() {
    }
}

whitelist.txt

192.168.1.45
192.168.1.47

web.xml

    <!-- WhiteList filter config -->
    <filter>
        <filter-name>WhiteListFilter</filter-name>
        <filter-class>com.toowards.sbr.WhiteListFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>WhiteListFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <!-- Put this before any servlet to restrict ip first -->