为什么ActiveMQ 5.14.x不能开始嵌入camel-jms组件2.18.3

Question

下面是一个简单的spring引导项目(版本1.5.2)来演示这个问题：

https://github.com/lanwen/camel-jms-activemq-test

它有Apache 版本2.18.3

在分支master上，由于activemq-camel=5.14.4和camel-jms=2.16.3 (从它那里得到过渡)，所有的工作都很好。

Spring引导应用程序通常以日志启动：

2017-04-22 00:53:19.647  INFO 97217 --- [           main] o.a.camel.spring.SpringCamelContext      : Apache Camel 2.18.3 (CamelContext: camel-1) is starting
2017-04-22 00:53:19.662  INFO 97173 --- [           main] o.apache.activemq.broker.BrokerService   : Apache ActiveMQ 5.14.4 (localhost, ID:lanwen-osx3.local-62145-1492811599544-0:1) is starting
2017-04-22 00:53:19.665  INFO 97173 --- [           main] o.apache.activemq.broker.BrokerService   : Apache ActiveMQ 5.14.4 (localhost, ID:lanwen-osx3.local-62145-1492811599544-0:1) started
2017-04-22 00:53:19.665  INFO 97173 --- [           main] o.apache.activemq.broker.BrokerService   : For help or more information please see: http://activemq.apache.org
2017-04-22 00:53:19.682  INFO 97173 --- [           main] o.a.activemq.broker.TransportConnector   : Connector vm://localhost started
2017-04-22 00:53:19.702  INFO 97173 --- [           main] o.a.camel.spring.SpringCamelContext      : Route: route1 started and consuming from: activemq://queue:to-write?asyncConsumer=true
2017-04-22 00:53:19.703  INFO 97173 --- [           main] o.a.camel.spring.SpringCamelContext      : Total 1 routes, of which 1 are started.
2017-04-22 00:53:19.704  INFO 97173 --- [           main] o.a.camel.spring.SpringCamelContext      : Apache Camel 2.18.3 (CamelContext: camel-1) started in 0.466 seconds
2017-04-22 00:53:19.709  INFO 97173 --- [           main] ru.yandex.test.writer.MyTestApplication  : Started MyTestApplication in 2.437 seconds (JVM running for 2.911)

但是当您从camel-jms=2.18.3开始(作为骆驼的主要版本，在分支工作中上)

这个日志出了问题：

2017-04-22 00:56:38.070  INFO 97195 --- [           main] o.a.camel.spring.SpringCamelContext      : Apache Camel 2.18.3 (CamelContext: camel-1) is starting
...
2017-04-22 00:56:43.590  WARN 97195 --- [ActiveMQ Task-1] o.a.a.t.failover.FailoverTransport       : Failed to connect to [tcp://localhost:61616] after: 10 attempt(s) continuing to retry.

但是如果我们用activemq-camel把5.13.4换成camel-jms=2.18.3，它又能正常工作了.

为什么ActiveMQ 5.14.x不适用于camel-jms 2.18.x

Answer 1

如果您查看最新的Camel ActiveMQ 1.15.5 (https://mvnrepository.com/artifact/org.apache.activemq/activemq-camel/5.14.5)的依赖列表，您会发现它已经将camel-jms作为依赖项，但版本是1.16.3。因此，不需要在POM中单独添加camel-jms 1.18.x依赖项，因为它将覆盖ActiveMQ已经使用的1.16.x版本，这是兼容的版本。

因此，从本质上讲，问题在于您试图使用一个更新的、不兼容的camel-jms版本。当您单独添加1.18.x camel-jms依赖项时，ActiveMQ组件将使用此版本，该版本与其1.16.x版本不兼容，因此出现错误。

如果您需要使用ActiveMQ，那么您可能需要查看camel-jms 1.16.x是否适合您。