我正在学习jedis，我无法确切找出此代码中的问题。任何人都可以帮助我。异常发生在语句tx.exec（）

public class JedisFactory {

 public static void main (String [] args){
     JedisPool pool = new JedisPool(new JedisPoolConfig(), "127.0.0.1", 6379);
     Jedis jedis = pool.getResource();

     Pipeline pipeline = jedis.pipelined();
     for(int i=0; i < 1000 ; i++){
         pipeline.hincrBy("Id", i+"", i);
     }
     pipeline.exec();        
     pool.returnResource(jedis);

     jedis = pool.getResource();
     Transaction tx = jedis.multi();
     Response<Map<String,String>> map = tx.hgetAll("Id");
     tx.hincrBy("Id","2", 1);
     **tx.exec();**
     //Map<String,String> map1 = jedis.hgetAll("Id");

     pool.returnResource(jedis);
     pool.destroy();
 }
}
Exception in thread "main" redis.clients.jedis.exceptions.JedisDataException: ERR EXEC without MULTI
    at redis.clients.jedis.Protocol.processError(Protocol.java:54)
    at redis.clients.jedis.Protocol.process(Protocol.java:61)
    at redis.clients.jedis.Protocol.read(Protocol.java:122)
    at redis.clients.jedis.Connection.getAll(Connection.java:207)
    at redis.clients.jedis.BinaryTransaction.exec(BinaryTransaction.java:23)
    at com.work.JedisFactory.main(JedisFactory.java:30)