Document H2CacheFactory class

Change-Id: Id5da602aede48ef1d8de58d812195bd059b71d50

java/com/google/gerrit/server/cache/h2/H2CacheFactory.java

diff --git a/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java b/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java
index 2b068aa..8f7e360 100644
--- a/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java
+++ b/java/com/google/gerrit/server/cache/h2/H2CacheFactory.java
@@ -47,6 +47,10 @@
 import java.util.concurrent.TimeUnit;
 import org.eclipse.jgit.lib.Config;
 
+/**
+ * Creates persistent caches depending on gerrit.config parameters. If the cache.directory property
+ * is unset, it will fall back to in-memory caches.
+ */
 @Singleton
 class H2CacheFactory implements PersistentCacheFactory, LifecycleListener {
   private static final FluentLogger logger = FluentLogger.forEnclosingClass();