Added support for key tags.

See http://code.google.com/p/redis/wiki/FAQ#I'm_using_some_form_of_key_hashing_for_partitioning,_but_wh

src/main/java/redis/clients/util/Sharded.java

@@ -4,11 +4,19 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.TreeMap;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 public class Sharded<R, S extends ShardInfo<R>> {
     public static final int DEFAULT_WEIGHT = 1;
     private TreeMap<Long, S> nodes;
     private final Hashing algo;
+    
+    /** 
+     * The default pattern used for extracting a key tag. 
+     * The pattern must have a group (between parenthesis), which delimits the tag to be hashed.
+     */
+    private Pattern tagPattern = Pattern.compile("\\{(.+?)\\}"); // the tag is anything between {} 
 
     public Sharded(List<S> shards) {
         this(shards, Hashing.MURMUR_HASH); // MD5 is really not good as we works with 64-bits not 128
@@ -19,6 +27,16 @@ public class Sharded<R, S extends ShardInfo<R>> {
         initialize(shards);
     }
 
+    public Sharded(List<S> shards, Pattern tagPattern) {
+        this(shards, Hashing.MURMUR_HASH, tagPattern); // MD5 is really not good as we works with 64-bits not 128
+    }
+
+    public Sharded(List<S> shards, Hashing algo, Pattern tagPattern) {
+        this.algo = algo;
+        this.tagPattern = tagPattern; 
+        initialize(shards);
+    }
+
     private void initialize(List<S> shards) {
         nodes = new TreeMap<Long, S>();
 
@@ -40,11 +58,26 @@ public class Sharded<R, S extends ShardInfo<R>> {
     }
 
     public R getShard(String key) {
-        return nodes.floorEntry(algo.hash(key)).getValue().getResource();
+        return nodes.floorEntry(algo.hash(getKeyTag(key))).getValue().getResource();
     }
 
     public S getShardInfo(String key) {
-        return nodes.floorEntry(algo.hash(key)).getValue();
+        return nodes.floorEntry(algo.hash(getKeyTag(key))).getValue();
+    }
+    
+    /**
+     * A key tag is a special pattern inside a key that, if preset, is the only part of the key hashed 
+     * in order to select the server for this key.
+     * 
+     * @see http://code.google.com/p/redis/wiki/FAQ#I'm_using_some_form_of_key_hashing_for_partitioning,_but_wh
+     * @param key
+     * @return The tag if it exists, or the original key 
+     */
+    public String getKeyTag(String key){
+    	Matcher m = tagPattern.matcher(key);
+    	if (m.find()) 
+    		return m.group(1); 
+    	return key; 
     }
 
     public Collection<S> getAllShards() {