public class TraceApplicationContext {
   private volatile static TraceApplicationContext instance = new TraceApplicationContext();
   private TraceApplicationContext() {

   }
   public static TraceApplicationContext getInstance() {
        return instance;
   }
}

public class SpoutA extends BaseRichSpout {
    public void open(Map map, TopologyContext topologyContext, SpoutOutputCollector spoutOutputCollector) {
        TraceApplicationContext.getInstance().init();
    }
}

public class BoltA extends BaseRichBolt {
   private static JedisCluster jedisCluster   = TraceApplicationContext.getInstance().getJedisCluster();
}

public class BoltB extends BaseRichBolt {
   private static JedisCluster jedisCluster   = TraceApplicationContext.getInstance().getJedisCluster();
}

public class MySingleton {
   private static MySingleton instance;
   private MySingleton() { ... }
   public static MySingleton getInstance() {
      if (instance == null) { instance = new MySingleton() }
      return instance;
   }
}

public enum MySingleton {
   INSTANCE;

   private MySingleton() {...}
}

public class MySingleton {
    private static volatile MySingleton instance;
    private MySingleton() { ... }
    public static MySingleton getInstance() {
        if (instance == null) {
            synchronized(MySingleton.class) {
                if (instance == null) {
                    instance = new MySingleton();
                }
            }
        }
        return instance;
    }
}