Cache recursos estaticos

import java.io.IOException;

import java.text.SimpleDateFormat;

import java.util.Calendar;

import java.util.Date;

import java.util.TimeZone;

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.HttpServletResponse;

private FilterConfig filterConfig;
    private String expires;
    private long nextDeploymentTime;

    public ExpiresFilter() {
            expires = nextDeploymentTime();
    }

    private String nextDeploymentTime() {
            // assume next deployment is M-F at 09:45
            Calendar c = Calendar.getInstance();

            int dayOffset = 1;
            
            if (c.get(Calendar.DAY_OF_WEEK) == Calendar.FRIDAY) {
                    dayOffset+=2;
            }
            
            if (c.get(Calendar.DAY_OF_WEEK) == Calendar.SATURDAY) {
                    dayOffset++;
            }
            
            c.add(Calendar.DAY_OF_MONTH, dayOffset);
            c.set(c.get(Calendar.YEAR)+2, c.get(Calendar.MONTH), 
                  c.get(Calendar.DAY_OF_MONTH), 9, 45);
            
            nextDeploymentTime = c.getTimeInMillis();
            
            String pattern = "EEE, dd MMM yyyy HH:mm:ss z";
            SimpleDateFormat sdf = new SimpleDateFormat(pattern);
            sdf.setTimeZone(TimeZone.getTimeZone("GMT"));
            return sdf.format(c.getTime());
    }
    
    private void addCacheHeaders(ServletRequest request, ServletResponse response)
            throws IOException, ServletException {
            
            HttpServletResponse sr = (HttpServletResponse) response;
            sr.setHeader("Expires", expires);
            long now = (new Date()).getTime();
            
            long expireTime = nextDeploymentTime - now;
            expireTime /= 1000;
            sr.setHeader("Cache-Control", "max-age="+
                    Long.toString(expireTime)+";public;must-revalidate;");
    }

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

            addCacheHeaders(request, response);
            chain.doFilter(request, response);
    }

 
    private FilterConfig getFilterConfig() {
            return filterConfig;
    }

  
    private void setFilterConfig(FilterConfig filterConfig) {
            this.filterConfig = filterConfig;
    }

  
    public void destroy() {
    }


    public void init(FilterConfig filterConfig) {
            setFilterConfig(filterConfig);
    }


    @Override
    public String toString() {
            if (getFilterConfig() == null) {
                    return ("ExpiresFilter()");
            }
            StringBuffer sb = new StringBuffer("ExpiresFilter(");
            sb.append(getFilterConfig());
            sb.append(")");
            return (sb.toString());

    }