1）什么是activemq？
acitvemq是遵循JMS规范的，面向消息的中间件（MOM）。出自apache旗下，无论在高可用，还是性能等方面，都是表现优异的。
The goal of ActiveMQ is to provide standards-based, message-oriented application
integration across as many languages and platforms as possible. ActiveMQ
implements the JMS spec and offers many additional features and value on top of
this spec. These additional features including items such as JMX management of
the broker, master/slave capability, message grouping, total ordering of messages,
consumer priority for location affinity, retroactive consumer feature for receiving
old messages upon subscription activation, handling for slow consumer situations,
virtual destinations to lower the number of required connections to the broker,
sophisticated message persistence, support for cursoring to handle large messages,
support for message transformation, support for the EIP patterns via Apache
Camel, mirrored queues for easier monitoring and much, much more.
2）activemq遵循jms规范，意味着：
synchronous or asynchronous message delivery, once-and-only-once message
delivery, message durability for subscribers and much more
3）activemq支持非常广泛的连接协议：HTTP/S, JGroups, JXTA, multicast, SSL, TCP, UDP,
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XMPP and more.
4）在应用系统交互中，可以提供清耦合的交互。