gistfile1.java

package fm.ask.infrastructure.caching;

import com.google.common.base.Supplier;
import com.google.common.base.Ticker;
import com.google.common.cache.CacheBuilder;
import com.rubylight.conf.IConfListener;
import com.rubylight.conf.IConfProperty;
import org.springframework.cache.Cache;
import org.springframework.cache.CacheManager;
import org.springframework.cache.guava.GuavaCacheManager;

import java.util.Collection;
import java.util.concurrent.TimeUnit;

import static com.google.common.base.Suppliers.memoize;

public class GuavaCacheManagerFactory extends CacheManagerFactory {

    private final String[] cacheName;
    private final IConfProperty<? extends CacheConfiguration> cacheConfiguration;
    private final Ticker ticker;


    public GuavaCacheManagerFactory(IConfProperty<? extends CacheConfiguration> configuration,
            Ticker ticker, String... cacheName) {
        this.cacheName = cacheName;
        this.cacheConfiguration = configuration;
        this.ticker = ticker;
    }

    @Override
    protected CacheManager createInstance() {
        // CacheManager initializes too early. At this stage we cannot access configuration, hence lazy loading.
        return new MemoizingCacheManager();

    }

    private class MemoizingCacheManager implements CacheManager {

        private final Supplier<CacheManager> cacheMemoizer = memoize(new CacheManagerSupplier());

        private class CacheManagerSupplier implements Supplier<CacheManager> {

            @Override
            public CacheManager get() {

                final GuavaCacheManager cacheManager = new GuavaCacheManager(cacheName);
                refreshConfiguration(cacheManager);

                cacheConfiguration.addPropertyListener(new IConfListener() {
                    @Override
                    public void changeProperty(String propertyKey) {
                        refreshConfiguration(cacheManager);
                    }
                });
                return cacheManager;
            }

            private void refreshConfiguration(GuavaCacheManager cacheManager) {
                long ttl = cacheConfiguration.getPropertyValue().getTtl();
                long size = cacheConfiguration.getPropertyValue().getSize();

                cacheManager.setCacheBuilder(CacheBuilder.newBuilder()
                        .ticker(ticker)
                        .maximumSize(size)
                        .expireAfterWrite(ttl, TimeUnit.SECONDS));
            }
        }

        @Override
        public Cache getCache(String name) {
            return cacheMemoizer.get().getCache(name);
        }

        @Override
        public Collection<String> getCacheNames() {
            return cacheMemoizer.get().getCacheNames();
        }

    }

}