activeMQ学习三

activeMQ的配置文件在/path/to/activemq/conf目录下面。

我的电脑上就在D:\apache-activemq-5.5.1\conf目录下，文件是activeMQ.xml。打开此文件：

<beans
  xmlns="http://www.springframework.org/schema/beans"
  xmlns:amq="http://activemq.org/config/1.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
  http://activemq.org/config/1.0 http://activemq.apache.org/schema/activemq-core.xsd
  http://activemq.apache.org/camel/schema/spring>
<!-- Allows us to use system properties as variables in this configuration file 
	在此配置文件中允许使用系统属性文件作为参数，即	
credentials.properties这个属性文件里存放一些参数，供此配置文件动态调用。
  -->
    <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations">
            <value>file:${activemq.base}/conf/credentials.properties</value>
        </property>      
    </bean>
   <!-- persistent="true"表示要持久化存储消息，和子元素persistenceAdapter结合使用 -->
   <!-- dataDirectory默认的存储持久化数据的目录 -->    <!-- brokerName 设置broker的name，在注意在网络上必须是唯一的-->
   <!--destroyApplicationContextOnStop="true" 表示当程序失效时是否需要停止-->
   <!-- 更多参考http://activemq.apache.org/xbean-xml-reference-50.html#XBeanXMLReference5.0-brokerelement -->
  <broker xmlns="http://activemq.org/config/1.0" brokerName="192.168.1.148" persistent ="true" 
       dataDirectory="${activemq.base}/data" useShutdownHook="false">
    <!-- Destination specific policies using destination names or wildcards -->
    <!-- wildcards意义见http://activemq.apache.org/wildcards.html -->
    <destinationPolicy>
      <policyMap>
        <policyEntries>
       <!-- 这里使用了wildcards，表示所有以EUCITA开头的topic -->
          <policyEntry topic="EUCITA.>" producerFlowControl="false" memoryLimit="10mb">
            <!-- 分发策略 -->
        <dispatchPolicy>
          <!-- 按顺序分发 -->
              <strictOrderDispatchPolicy/>
            </dispatchPolicy>
        <!--  恢复策略-->
            <subscriptionRecoveryPolicy>
          <!-- 只恢复最后一个message -->
              <lastImageSubscriptionRecoveryPolicy/>
            </subscriptionRecoveryPolicy>
          </policyEntry>
        </policyEntries>
      </policyMap>
    </destinationPolicy>

    <!-- The transport connectors ActiveMQ will listen to -->
    <transportConnectors>
       <transportConnector name="openwire" uri="tcp://192.168.1.148:61616" discoveryUri="multicast://default"/>
    </transportConnectors>
   
    <!-- 消息持久化方式 -->
    <persistenceAdapter>
      <amqPersistenceAdapter directory="${activemq.base}/data"/>
    </persistenceAdapter>
</broker>

  <!-- lets create a command agent to respond to message based admin commands on the ActiveMQ.Agent topic -->
    <commandAgent xmlns="http://activemq.org/config/1.0"/>
  
  <!-- An embedded servlet engine for serving up the Admin console -->
  <jetty xmlns="http://mortbay.com/schemas/jetty/1.0">
    <connectors>
      <nioConnector port="8161" />
    </connectors>

    <handlers>
      <webAppContext contextPath="/admin" resourceBase="${activemq.base}/webapps/admin" logUrlOnStart="true" />     
      <webAppContext contextPath="/demo" resourceBase="${activemq.base}/webapps/demo" logUrlOnStart="true" />       
    </handlers>
  </jetty> 
</beans>

在这里重点讲解几个属性：

DispathPolicy

ActiveMQ支持3中不同的分发策略（避免翻译了以后误解，这里用原文）：

1. <roundRobinDispatchPolicy>：Simple dispatch policy that sends a message to every subscription that matches the message.
2. <simpleDispatchPolicy>：Simple dispatch policy that sends a message to every subscription that matches the message.
3. <strictOrderDispatchPolicy>：Dispatch policy that causes every subscription to see messages in the same order.

SubscriptionRecoveryPolicy

ActiveMQ支持6种恢复策略，可以自行选择使用不同的策略

1. <fixedCountSubscriptionRecoveryPolicy>： keep a fixed count of last messages.
2. <fixedSizedSubscriptionRecoveryPolicy>： keep a fixed amount of memory available in RAM for message history which is evicted in time order.
3. <lastImageSubscriptionRecoveryPolicy>：only keep the last message.
4. <noSubscriptionRecoveryPolicy>：disable recovery of messages.
5. <queryBasedSubscriptionRecoveryPolicy>：perform a user specific query mechanism to load any messages they may have missed.
6. <timedSubscriptionRecoveryPolicy>：keep a timed buffer of messages around in memory and use that to recover new subscriptions.

PersistenceAdapter

http://activemq.apache.org/persistence 讲解了关于persistence的信息。ActiveMQ5.5.1使用AMQ Message Store 持久化消息，这种方式提供了很好的性能（The AMQ Message Store is an embeddable transactional message storage solution that is extremely fast and reliable.） 默认使用该存储方式即可，如果想使用JDBC来存储，可以查找文档配置。

 

这里只是讲解核心配置文件大概，具体细节并没有详解，而activeMQ的配置文件是要根据实际情况来配置的，以下通过一个实例

服务端（Shared File SystemMaster Slave）+ 客户端（failover transport）
来具体分析activeMQ该如何配置。