一致性hash算法(JAVA)

 本文来自http://www.iteye.com/topic/1132274，版权原作者所有

Java代码
public class ConsistentHash<T> { 
 
       private final HashFunction hashFunction; 
       private final int numberOfReplicas; 
       private final SortedMap<Integer, T> circle = new TreeMap<Integer, T>(); 
 
       public ConsistentHash(HashFunction hashFunction, int numberOfReplicas, Collection<T> nodes) { 
             this .hashFunction = hashFunction; 
             this .numberOfReplicas = numberOfReplicas; 
 
             for (T node : nodes) { 
                  add(node); 
            } 
      } 
 
       public void add(T node) { 
             for (int i = 0; i < numberOfReplicas; i++) { 
                   circle .put(hashFunction .hash(node.toString() + i), node); 
            } 
      } 
 
       public void remove(T node) { 
             for (int i = 0; i < numberOfReplicas; i++) { 
                   circle .remove(hashFunction .hash(node.toString() + i)); 
            } 
      } 
 
       public T get(Object key) { 
             if (circle .isEmpty()) { 
                   return null ; 
            } 
             int hash = hashFunction .hash(key); 
             // System.out.println("hash---: " + hash); 
             if (!circle .containsKey(hash)) { 
                  SortedMap<Integer, T> tailMap = circle .tailMap(hash); 
                  hash = tailMap.isEmpty() ? circle .firstKey() : tailMap.firstKey(); 
            } 
             // System.out.println("hash---: " + hash); 
             return circle .get(hash); 
      } 
 
       static class HashFunction { 
             int hash(Object key) {
                   //md5加密后，hashcode
                   return Md5Encrypt.md5(key.toString()).hashCode(); 
            } 
      } 
 
       public static void main(String [] args) { 
            HashSet< String> set = new HashSet< String>(); 
            set.add( "A" ); 
            set.add( "B" ); 
            set.add( "C" ); 
            set.add( "D" ); 
 
            Map< String, Integer> map = new HashMap< String, Integer>(); 
 
            ConsistentHash< String> consistentHash = new ConsistentHash<String>( new HashFunction(), 1000, set); 
 
             int count = 10000; 
 
             for (int i = 0; i < count; i++) { 
                   String key = consistentHash.get(i); 
                   if (map.containsKey(key)) { 
                        map.put(consistentHash.get(i), map.get(key) + 1); 
                  } else { 
                        map.put(consistentHash.get(i), 1); 
                  } 
                   // System.out.println(key); 
            } 
 
             showServer(map); 
            map.clear(); 
            consistentHash.remove( "A" ); 
 
            System. out .println("------- remove A" ); 
 
             for (int i = 0; i < count; i++) { 
                   String key = consistentHash.get(i); 
                   if (map.containsKey(key)) { 
                        map.put(consistentHash.get(i), map.get(key) + 1); 
                  } else { 
                        map.put(consistentHash.get(i), 1); 
                  } 
                   // System.out.println(key); 
            } 
 
             showServer(map); 
            map.clear(); 
            consistentHash.add( "E" ); 
            System. out .println("------- add E" ); 
 
             for (int i = 0; i < count; i++) { 
                   String key = consistentHash.get(i); 
                   if (map.containsKey(key)) { 
                        map.put(consistentHash.get(i), map.get(key) + 1); 
                  } else { 
                        map.put(consistentHash.get(i), 1); 
                  } 
                   // System.out.println(key); 
            } 
 
             showServer(map); 
            map.clear(); 
 
            consistentHash.add( "F" ); 
            System. out .println("------- add F服务器  业务量加倍" ); 
            count = count * 2; 
             for (int i = 0; i < count; i++) { 
                  String key = consistentHash.get(i); 
                   if (map.containsKey(key)) { 
                        map.put(consistentHash.get(i), map.get(key) + 1); 
                  } else { 
                        map.put(consistentHash.get(i), 1); 
                  } 
                   // System.out.println(key); 
            } 
 
             showServer(map); 
 
      } 
 
       public static void showServer(Map<String , Integer> map) { 
             for (Entry<String, Integer> m : map.entrySet()) { 
                  System. out .println("服务器 " + m.getKey() + "----" + m.getValue() + "个" ); 
            } 
      } 
 
}