Convert nulls to instances of a special NullValue class when we store them, and back again when retrieved. EHCache's replication mechanism flips out if you cache actual nulls (I have no idea why, nulls are obviously serializable). Also fix up some comments -- very soon we are going to have to add better (probably runtime) configurability to the Caches, and probably also write some code to display/collate their statistics.

git-svn-id: https://samskivert.googlecode.com/svn/trunk@2257 6335cc39-0255-0410-8fd6-9bcaacd3b74c

src/java/com/samskivert/jdbc/depot/EHCacheAdapter.java

@@ -72,7 +72,9 @@ public class EHCacheAdapter
                 return null;
             }
 
-            @SuppressWarnings("unchecked") final T value = (T) hit.getValue();
+            Serializable rawValue = hit.getValue();
+            @SuppressWarnings("unchecked")
+                final T value = (T) (rawValue instanceof NullValue ? null : rawValue);
             return new CachedValue<T>() {
                 public T getValue () {
                     return value;
@@ -86,7 +88,7 @@ public class EHCacheAdapter
         // from CacheBin
         public void store (Serializable key, T value)
         {
-            _cache.put(new Element(key, value));
+            _cache.put(new Element(key, value != null ? value : NULL));
         }
 
         // from CacheBin
@@ -106,12 +108,19 @@ public class EHCacheAdapter
         {
             _cache = _cachemgr.getCache(id);
             if (_cache == null) {
-                _cache = new Cache(id, 5000, false, false, 600, 60);
+                // create the cache programatically with reasonable settings
+                // TODO: we will eventually need this to be configurable in .properties
+
+                _cache = new Cache(id,
+                    5000,       // keep 5000 elements in RAM
+                    true,       // overflow the rest to disk
+                    false,      // don't keep records around eternally
+                    600,        // but do keep them for 10 minutes after they're created
+                    60);        // or 1 minute after last access
 
                 if (_distributed) {
-                    // for reasons unknown we have to add this event listener programmatically
-                    // rather than include it in the defaultCache portion of the ehcache.xml
-                    // configuration file.
+                    // a programatically created cache has to have its replicator event listener
+                    // programatically added.
                     _cache.getCacheEventNotificationService().registerListener(
                         new RMIAsynchronousCacheReplicator(true, true, true, true, 1000));
                 }
@@ -130,4 +139,26 @@ public class EHCacheAdapter
 
     protected boolean _distributed;
     protected CacheManager _cachemgr;
+
+    // this is just for convenience and memory use; we don't rely on pointer equality anywhere
+    protected static Serializable NULL = new NullValue() {};
+
+    /** A class to represent an explicitly Serializable concept of null for EHCache. */
+    protected static class NullValue implements Serializable
+    {
+        public String toString ()
+        {
+            return "<EHCache Null>";
+        }
+
+        public boolean equals (Object other)
+        {
+            return other != null && other.getClass().equals(NullValue.class);
+        }
+
+        public int hashCode ()
+        {
+            return 1;
+        }
+    }
 }