content: package com.xxl.job.admin.core.route.strategy;
  
  import com.xxl.job.admin.core.route.ExecutorRouter;
  import com.xxl.job.admin.core.trigger.XxlJobTrigger;
  import com.xxl.job.core.biz.model.ReturnT;
  import com.xxl.job.core.biz.model.TriggerParam;
  
  import java.io.UnsupportedEncodingException;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.ArrayList;
  import java.util.SortedMap;
  import java.util.TreeMap;
  
  /**
   * 分组下机器地址相同，不同JOB均匀散列在不同机器上，保证分组下机器分配JOB平均；且每个JOB固定调度其中一台机器；
   *      a、virtual node：解决不均衡问题
   *      b、hash method replace hashCode：String的hashCode可能重复，需要进一步扩大hashCode的取值范围
   * Created by xuxueli on 17/3/10.
   */
  public class ExecutorRouteConsistentHash extends ExecutorRouter {
  
      private static int VIRTUAL_NODE_NUM = 5;
  
      /**
       * get hash code on 2^32 ring (md5散列的方式计算hash值)
       * @param key
       * @return
       */
      private static long hash(String key) {
  
          // md5 byte
          MessageDigest md5;
          try {
              md5 = MessageDigest.getInstance("MD5");
          } catch (NoSuchAlgorithmException e) {
              throw new RuntimeException("MD5 not supported", e);
          }
          md5.reset();
          byte[] keyBytes = null;
          try {
              keyBytes = key.getBytes("UTF-8");
          } catch (UnsupportedEncodingException e) {
              throw new RuntimeException("Unknown string :" + key, e);
          }
  
          md5.update(keyBytes);
          byte[] digest = md5.digest();
  
          // hash code, Truncate to 32-bits
          long hashCode = ((long) (digest[3] & 0xFF) << 24)
                  | ((long) (digest[2] & 0xFF) << 16)
                  | ((long) (digest[1] & 0xFF) << 8)
                  | (digest[0] & 0xFF);
  
          long truncateHashCode = hashCode & 0xffffffffL;
          return truncateHashCode;
      }
  
      public String route(int jobId, ArrayList<String> addressList) {
  
          // ------A1------A2-------A3------
          // -----------J1------------------
          TreeMap<Long, String> addressRing = new TreeMap<Long, String>();
          for (String address: addressList) {
              for (int i = 0; i < VIRTUAL_NODE_NUM; i++) {
                  long addressHash = hash("SHARD-" + address + "-NODE-" + i);
                  addressRing.put(addressHash, address);
              }
          }
  
          long jobHash = hash(String.valueOf(jobId));
          SortedMap<Long, String> lastRing = addressRing.tailMap(jobHash);
          if (!lastRing.isEmpty()) {
              return lastRing.get(lastRing.firstKey());
          }
          return addressRing.firstEntry().getValue();
      }
  
      @Override
      public ReturnT<String> routeRun(TriggerParam triggerParam, ArrayList<String> addressList) {
          // address
          String address = route(triggerParam.getJobId(), addressList);
  
          // run executor
          ReturnT<String> runResult = XxlJobTrigger.runExecutor(triggerParam, address);
          runResult.setContent(address);
          return runResult;
      }
  }
  