CachingHttpHeadersFilter.java

package com.dangdang.mypp.web.filter;

import org.springframework.core.env.Environment;

import javax.servlet.*;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.concurrent.TimeUnit;

/**
 * This filter is used in production, to put HTTP cache headers with a long (1 month) expiration time.
 * </p>
 */
public class CachingHttpHeadersFilter implements Filter {

    // We consider the last modified date is the start up time of the server
    private final static long LAST_MODIFIED = System.currentTimeMillis();

    private long CACHE_TIME_TO_LIVE = TimeUnit.DAYS.toMillis(31L);

    private Environment env;

    public CachingHttpHeadersFilter(Environment env) {
           this.env = env;
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        CACHE_TIME_TO_LIVE = TimeUnit.DAYS.toMillis(env.getProperty("http.cache.timeToLiveInDays", Long.class, 31L));
    }

    @Override
    public void destroy() {
        // Nothing to destroy
    }

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

        httpResponse.setHeader("Cache-Control", "max-age=" + CACHE_TIME_TO_LIVE + ", public");
        httpResponse.setHeader("Pragma", "cache");

        // Setting Expires header, for proxy caching
        httpResponse.setDateHeader("Expires", CACHE_TIME_TO_LIVE + System.currentTimeMillis());

        // Setting the Last-Modified header, for browser caching
        httpResponse.setDateHeader("Last-Modified", LAST_MODIFIED);

        chain.doFilter(request, response);
    }
}