can high-level consumer api provide the method getting messages with non-block?

[zlai_2001]

hi:
     I use high-level consumer api to get message. But I want to use non-block 
method. Below is the code:
 
       ConsumerConnector consumer =  
kafka.consumer.Consumer.createJavaConsumerConnector(consumerconfig); 
    Map<String, Integer> topicCountMap = new HashMap<String, Integer>();
    topicCountMap.put("topic", new Integer(1));
    Map<String, List<KafkaMessageStream<Message>>> consumerMap = 
consumer.createMessageStreams(topicCountMap);
    KafkaMessageStream<Message> stream =  consumerMap.get("topic").get(0);
    ConsumerIterator<Message> it = stream.iterator();
    while(it.hasNext())
    {
     ByteBuffer buffer = it.next().payload();
     byte [] bytes = new byte[buffer.remaining()];
     buffer.get(bytes);
     System.out.println(new String(bytes));
    }

The problem is that when there are no message,the program is blocked at 
"it.hasNext()";But I want to break out.  Are there some methods?
Thanks!