CacheWhileOnSessionFilter.java

package jp.co.aflac.util;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Cache resources on clinet while a user session is valid.
 * 
 * @author sndyuk
 */
public class CacheWhileOnSessionFilter implements Filter {

    private static final String SESSION_EXPIRATION_TIME = "session_expiration_time";

    /**
     * {@inheritDoc}
     */
    @Override
    public void init(final FilterConfig filterConfig) throws ServletException {
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain) throws IOException, ServletException {
        chain.doFilter(request, response);

        HttpServletRequest httpReq = (HttpServletRequest) request;
        HttpServletResponse httpRes = (HttpServletResponse) response;
        HttpSession session = httpReq.getSession(false);
        if (session == null) {
            httpRes.setHeader("Cache-Control", "no-cache");
            httpRes.setHeader("Pragma", "no-cache, no-store");
            httpRes.setDateHeader("Expires", System.currentTimeMillis());
            return;
        }
        long sessionExpirationTime;
        if (session.isNew()) {
            sessionExpirationTime = session.getLastAccessedTime() + (session.getMaxInactiveInterval() * 1000);
            session.setAttribute(SESSION_EXPIRATION_TIME, sessionExpirationTime);
        } else {
            sessionExpirationTime = (long) session.getAttribute(SESSION_EXPIRATION_TIME);
        }
        httpRes.setHeader("Cache-Control", "max-age=" + (sessionExpirationTime - System.currentTimeMillis()));
        httpRes.setDateHeader("Expires", sessionExpirationTime);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void destroy() {
    }
}