content: package com.xxl.job.admin.core.route.strategy;
  
  import com.xxl.job.admin.core.route.ExecutorRouter;
  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.List;
  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 = 100;
  
  	/**
  	 * 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 hashJob(int jobId, List<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> route(TriggerParam triggerParam, List<String> addressList) {
  		String address = hashJob(triggerParam.getJobId(), addressList);
  		return new ReturnT<String>(address);
  	}
  
  }
  