如何在无法访问MQTT服务器的情况下启动camel

Question

我想让我的Apache Camel应用程序更具弹性，即使无法访问MQTT代理，也可以启动它。我们正在物联网设备上使用Camel，其互联网连接可能不稳定，我希望我们的应用程序即使没有互联网接入也能启动。

示例性路线如下所示：

from("timer:heartbeat?period=5000")
    .routeId("send heartbeat")
    .setBody(simple("Hello World!"))
    .to("paho:myhostnome/heartbeat?brokerUrl={{broker.url}}")

只要MQTT服务器可用，这就可以正常工作。但是，当无法访问服务器时，上下文会在预热PahoEndpoint时失败。

Caused by: org.apache.camel.FailedToCreateRouteException: Failed to create route send heartbeat: Route(send heartbeat)[[From[timer:heartbeat?period={{heartbe... because of Unable to connect to server
at org.apache.camel.impl.RouteService.warmUp(RouteService.java:147) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.doWarmUpRoutes(DefaultCamelContext.java:3758) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.safelyStartRouteServices(DefaultCamelContext.java:3665) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.doStartOrResumeRoutes(DefaultCamelContext.java:3451) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.doStartCamel(DefaultCamelContext.java:3305) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.access$000(DefaultCamelContext.java:202) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext$2.call(DefaultCamelContext.java:3089) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext$2.call(DefaultCamelContext.java:3085) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.doWithDefinedClassLoader(DefaultCamelContext.java:3108) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.doStart(DefaultCamelContext.java:3085) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.support.ServiceSupport.start(ServiceSupport.java:61) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.impl.DefaultCamelContext.start(DefaultCamelContext.java:3022) ~[camel-core-2.19.3.jar:2.19.3]
at org.apache.camel.spring.boot.RoutesCollector.maybeStart(RoutesCollector.java:242) ~[camel-spring-boot-2.19.3.jar:2.19.3]
at org.apache.camel.spring.boot.RoutesCollector.onApplicationEvent(RoutesCollector.java:217) ~[camel-spring-boot-2.19.3.jar:2.19.3]
... 13 common frames omitted
Caused by: org.eclipse.paho.client.mqttv3.MqttException: Unable to connect to server
at org.eclipse.paho.client.mqttv3.internal.TCPNetworkModule.start(TCPNetworkModule.java:79) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:na]
at org.eclipse.paho.client.mqttv3.internal.ClientComms$ConnectBG.run(ClientComms.java:650) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:na]
at java.lang.Thread.run(Thread.java:745) ~[na:1.8.0_121]
Caused by: java.net.ConnectException: Connection refused (Connection refused)
at java.net.PlainSocketImpl.socketConnect(Native Method) ~[na:1.8.0_121]
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350) ~[na:1.8.0_121]
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206) ~[na:1.8.0_121]
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188) ~[na:1.8.0_121]
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:1.8.0_121]
at java.net.Socket.connect(Socket.java:589) ~[na:1.8.0_121]
at org.eclipse.paho.client.mqttv3.internal.TCPNetworkModule.start(TCPNetworkModule.java:70) ~[org.eclipse.paho.client.mqttv3-1.1.0.jar:na]

我的第一个想法是在所有涉及Paho的路线上禁用自动启动，然后手动启动。这不起作用，因为即使路线本身未启动，PahoEndpoint也已启动。

我现在正在寻找另一种方法来处理这个问题。

Answer 1

Camel具有try（）catch（）功能。

为什么不在调用to（）之前添加一个try（），捕获异常，然后记录它呢？比如：

from("timer:heartbeat?period=5000")
    .routeId("send heartbeat")
    .setBody(simple("Hello World!"))
    .doTry()
    .to("paho:myhostnome/heartbeat?brokerUrl={{broker.url}}")
     .doCatch( java.net.ConnectException.class).log("failed")
    .end()

Answer 2

Apache Camel 2.20以后的版本提供了一个新功能，可以让启动过程使用一个superviser控制器来运行，该控制器负责从CamelContext本身启动。这允许设置更高级的配置，让控制器处理错误，并尝试重新启动失败的路由等。

有一个例子，它是通过Spring Boot配置的，但您也可以通过Java API进行配置：https://github.com/apache/camel/tree/master/examples/camel-example-spring-boot-supervising-route-controller

在即将发布的版本中，我们将改进这个新功能。对于旧版本的Camel，通常组件本身可能提供也可能不提供任何类型的重试机制，您需要配置，而不是快速失败。