Redis集群批量操作-蒲公英云

Redis集群批量操作

  众所周知，Redis集群是没法执行批量操作命令的，如mget，pipeline等。这是因为redis将集群划分为16383个哈希槽，不同的key会划分到不同的槽中。但是，Jedis客户端提供了计算key的slot方法，已经slot和节点之间的映射关系，通过这两个数据，就可以计算出每个key所在的节点，然后使用pipeline获取数据。具体代码如下：
/**
 * 根据key计算slot，再根据slot计算node，获取pipeline
 * 进行批量操作 
 */
public class BatchUtil {
    public static Map<String,String> mget(JedisCluster jc,String... keys){
        Map<String,String> resMap = new HashMap<>();
        if(keys == null || keys.length == 0){
            return resMap;
        }
        //如果只有一条，直接使用get即可
        if(keys.length == 1){
            resMap.put(keys[0],jc.get(keys[0]));
            return resMap;
        }
        //JedisCluster继承了BinaryJedisCluster
        //BinaryJedisCluster的JedisClusterConnectionHandler属性
        //里面有JedisClusterInfoCache，根据这一条继承链，可以获取到JedisClusterInfoCache
        //从而获取slot和JedisPool直接的映射
        MetaObject metaObject = SystemMetaObject.forObject(jc);
        JedisClusterInfoCache cache = (JedisClusterInfoCache) metaObject.getValue("connectionHandler.cache");
        //保存地址+端口和命令的映射
        Map<JedisPool,List<String>> jedisPoolMap = new HashMap<>();
        List<String> keyList = null;
        JedisPool currentJedisPool = null;
        Pipeline currentPipeline = null;
        for(String key:keys){
            //计算哈希槽
            int crc = JedisClusterCRC16.getSlot(key);
            //通过哈希槽获取节点的连接
            currentJedisPool = cache.getSlotPool(crc);
            //由于JedisPool作为value保存在JedisClusterInfoCache中的一个map对象中，每个节点的
            //JedisPool在map的初始化阶段就是确定的和唯一的，所以获取到的每个节点的JedisPool都是一样
            //的，可以作为map的key
            if(jedisPoolMap.containsKey(currentJedisPool)){
                jedisPoolMap.get(currentJedisPool).add(key);
            }else{
                keyList = new ArrayList<>();
                keyList.add(key);
                jedisPoolMap.put(currentJedisPool, keyList);
            }
        }
        //保存结果
        List<Object> res = new ArrayList<>();
        //执行
        for(Entry<JedisPool,List<String>> entry:jedisPoolMap.entrySet()){
            try {
                currentJedisPool = entry.getKey();
                keyList = entry.getValue();
                //获取pipeline
                currentPipeline = currentJedisPool.getResource().pipelined();
                for(String key:keyList){
                    currentPipeline.get(key);
                }
                //从pipeline中获取结果
                res = currentPipeline.syncAndReturnAll();
                currentPipeline.close();
                for(int i=0;i<keyList.size();i++){
                    resMap.put(keyList.get(i),res.get(i)==null?null:res.get(i).toString());
                }
            } catch (Exception e) {
                e.printStackTrace();
                return new HashMap<>();
            }
        }
        return resMap;
    }
}