ActiveMQ持久化消息

ActiveMQ的另一个问题就是只要是软件就有可能挂掉，挂掉不可怕，怕的是挂掉之后把信息给丢了，所以本节分析一下几种持久化方式：

一、持久化为文件

ActiveMQ默认就支持这种方式，只要在发消息时设置消息为持久化就可以了。

打开安装目录下的配置文件：

D:\ActiveMQ\apache-activemq\conf\activemq.xml在越80行会发现默认的配置项：

</persistenceAdapter>

注意这里使用的是kahaDB，是一个基于文件支持事务的消息存储器，是一个可靠，高性能，可扩展的消息存储器。

他的设计初衷就是使用简单并尽可能的快。KahaDB的索引使用一个transaction log，并且所有的destination只使用一个index，有人测试表明：如果用于生产环境，支持1万个active connection，每个connection有一个独立的queue。该表现已经足矣应付大部分的需求。

然后再发送消息的时候改变第二个参数为：

MsgDeliveryMode.Persistent

Message保存方式有2种 PERSISTENT：保存到磁盘，consumer消费之后，message被删除。 NON_PERSISTENT：保存到内存，消费之后message被清除。注意：堆积的消息太多可能导致内存溢出。

然后打开生产者端发送一个消息：

不启动消费者端，同时在管理界面查看：

发现有一个消息正在等待，这时如果没有持久化，ActiveMQ宕机后重启这个消息就是丢失，而我们现在修改为文件持久化，重启ActiveMQ后消费者仍然能够收到这个消息。

二、持久化为数据库

我们从支持Mysql为例，先从http://dev.mysql.com/downloads/connector/j/下载mysql-connector-java-5.1.34-bin.jar包放到：

D:\ActiveMQ\apache-activemq\lib目录下。

打开并修改配置文件：

<beans
  xmlns="http://www.springframework.org/schema/beans"
  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.xsd
  http://activemq.apache.org/schema/core http://activemq.apache.org/schema/core/activemq-core.xsd">

    <!-- Allows us to use system properties as variables in this configuration file -->
    <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations">
            <value>file:${activemq.conf}/credentials.properties</value>
        </property>
    </bean>

   <!-- Allows accessing the server log -->
    <bean id="logQuery" class="org.fusesource.insight.log.log4j.Log4jLogQuery"
          lazy-init="false" scope="singleton"
          init-method="start" destroy-method="stop">
    </bean>

    <!--
        The <broker> element is used to configure the ActiveMQ broker.
    -->
    <broker xmlns="http://activemq.apache.org/schema/core" brokerName="localhost" dataDirectory="${activemq.data}">

        <destinationPolicy>
            <policyMap>
              <policyEntries>
                <policyEntry topic=">" >
                    <!-- The constantPendingMessageLimitStrategy is used to prevent
                         slow topic consumers to block producers and affect other consumers
                         by limiting the number of messages that are retained
                         For more information, see:

                         http://activemq.apache.org/slow-consumer-handling.html

                    -->
                  <pendingMessageLimitStrategy>
                    <constantPendingMessageLimitStrategy limit="1000"/>
                  </pendingMessageLimitStrategy>
                </policyEntry>
              </policyEntries>
            </policyMap>
        </destinationPolicy>


        <!--
            The managementContext is used to configure how ActiveMQ is exposed in
            JMX. By default, ActiveMQ uses the MBean server that is started by
            the JVM. For more information, see:

            http://activemq.apache.org/jmx.html
        -->
        <managementContext>
            <managementContext createConnector="false"/>
        </managementContext>

        <!--
            Configure message persistence for the broker. The default persistence
            mechanism is the KahaDB store (identified by the kahaDB tag).
            For more information, see:

            http://activemq.apache.org/persistence.html
            <kahaDB directory="${activemq.data}/kahadb"/>
        -->
        <persistenceAdapter>
            <jdbcPersistenceAdapter dataDirectory="${activemq.base}/data" dataSource="#derby-ds"/>
        </persistenceAdapter>


          <!--
            The systemUsage controls the maximum amount of space the broker will
            use before disabling caching and/or slowing down producers. For more information, see:
            http://activemq.apache.org/producer-flow-control.html
          -->
          <systemUsage>
            <systemUsage>
                <memoryUsage>
                    <memoryUsage percentOfJvmHeap="70" />
                </memoryUsage>
                <storeUsage>
                    <storeUsage limit="100 gb"/>
                </storeUsage>
                <tempUsage>
                    <tempUsage limit="50 gb"/>
                </tempUsage>
            </systemUsage>
        </systemUsage>

        <!--
            The transport connectors expose ActiveMQ over a given protocol to
            clients and other brokers. For more information, see:

            http://activemq.apache.org/configuring-transports.html
        -->
        <transportConnectors>
            <!-- DOS protection, limit concurrent connections to 1000 and frame size to 100MB -->
            <transportConnector name="openwire" uri="tcp://0.0.0.0:61616?maximumConnections=1000&amp;wireFormat.maxFrameSize=104857600"/>
            <transportConnector name="amqp" uri="amqp://0.0.0.0:5672?maximumConnections=1000&amp;wireFormat.maxFrameSize=104857600"/>
            <transportConnector name="stomp" uri="stomp://0.0.0.0:61613?maximumConnections=1000&amp;wireFormat.maxFrameSize=104857600"/>
            <transportConnector name="mqtt" uri="mqtt://0.0.0.0:1883?maximumConnections=1000&amp;wireFormat.maxFrameSize=104857600"/>
            <transportConnector name="ws" uri="ws://0.0.0.0:61614?maximumConnections=1000&amp;wireFormat.maxFrameSize=104857600"/>
        </transportConnectors>

        <!-- destroy the spring context on shutdown to stop jetty -->
        <shutdownHooks>
            <bean xmlns="http://www.springframework.org/schema/beans" class="org.apache.activemq.hooks.SpringContextHook" />
        </shutdownHooks>

    </