转自：http://www.changeself.net/archives/rocketmq入门（3）拉取消息.html
RocketMQ不止可以直接推送消息，在消费端注册监听器进行监听，还可以由消费端决定自己去拉取数据
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/**
* PullConsumer，订阅消息
*/
public
class
PullConsumer
{
//Java缓存
private
static
final
Map<MessageQueue,
Long>
offseTable
=
new
HashMap<MessageQueue,
Long>();
public
static
void
main(String[]
args)
throws
MQClientException
{
DefaultMQPullConsumer
consumer
=
new
DefaultMQPullConsumer("PullConsumerGroup");
consumer.setNamesrvAddr("127.0.0.1:9876");
consumer.start();
//拉取订阅主题的队列，默认队列大小是4
Set<MessageQueue>
mqs
=
consumer.fetchSubscribeMessageQueues("TopicTestMapBody");
for
(MessageQueue
mq
:
mqs)
{
System.out.println("Consume
from the queue: "
+
mq);
SINGLE_MQ:while(true){
try
{
PullResult
pullResult
=
consumer.pullBlockIfNotFound(mq,
null,
getMessageQueueOffset(mq),
32);
List<MessageExt>
list=pullResult.getMsgFoundList();
if(list!=null&&list.size()<100){
for(MessageExt
msg:list){
System.out.println(SerializableInterface.deserialize(msg.getBody()));
}
}
System.out.println(pullResult.getNextBeginOffset());
putMessageQueueOffset(mq,
pullResult.getNextBeginOffset());
switch
(pullResult.getPullStatus())
{
case
FOUND:
//
TODO
break;
case
NO_MATCHED_MSG:
break;
case
NO_NEW_MSG:
break
SINGLE_MQ;
case
OFFSET_ILLEGAL:
break;
default:
break;
}
}
catch
(Exception
e)
{
e.printStackTrace();
}
}
}
consumer.shutdown();
}
private
static
void
putMessageQueueOffset(MessageQueue
mq,
long
offset)
{
offseTable.put(mq,
offset);
}
private
static
long
getMessageQueueOffset(MessageQueue
mq)
{
Long
offset
=
offseTable.get(mq);
if
(offset
!=
null){
System.out.println(offset);
return
offset;
}
return
0;
}
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刚开始的没有细看PullResult对象，以为拉取到的结果没有MessageExt对象还跑到群里面问别人，犯2了
特别要注意 静态变量offsetTable的作用，拉取的是按照从offset（理解为下标）位置开始拉取，拉取N条，offsetTable记录下次拉取的offset位置