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一致性hash算法的原理
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" );              }        }  }
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