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
;
}
|
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