如何通过 Tomcat 使用 MQTT

Question

我想在 tomcat8 中使用 MQTT，以便通过 MQTT 发布消息。我使用 Paho 库版本 3.1.1。当我尝试使用

实例化客户端时

String clientId = Mqtt.generateClientId(); 
MqttClient client = new MqttClient("tcp://localhost:1883", clientId);

我收到 MqttException(0)。

下面是错误消息和堆栈跟踪的详细信息：

reason 0
msg MqttException
loc MqttException
cause null
excep MqttException (0)
MqttException (0)
    at org.eclipse.paho.client.mqttv3.persist.MqttDefaultFilePersistence.open(MqttDefaultFilePersistence.java:80)
    at org.eclipse.paho.client.mqttv3.MqttAsyncClient.<init>(MqttAsyncClient.java:304)
    at org.eclipse.paho.client.mqttv3.MqttAsyncClient.<init>(MqttAsyncClient.java:185)
    at org.eclipse.paho.client.mqttv3.MqttClient.<init>(MqttClient.java:226)
    at org.eclipse.paho.client.mqttv3.MqttClient.<init>(MqttClient.java:138)
    at de.rz.homeautomation.service.HomeAutomationService.publishSensorData(HomeAutomationService.java:807)
    at de.rz.homeautomation.service.HomeAutomationService.postSensorData(HomeAutomationService.java:857)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory.invoke(ResourceMethodInvocationHandlerFactory.java:81)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.run(AbstractJavaResourceMethodDispatcher.java:151)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:171)
    at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$ResponseOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:152)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:104)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:387)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:331)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:103)
    at org.glassfish.jersey.server.ServerRuntime.run(ServerRuntime.java:271)
    at org.glassfish.jersey.internal.Errors.call(Errors.java:271)
    at org.glassfish.jersey.internal.Errors.call(Errors.java:267)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:297)
    at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:254)
    at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1030)
    at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:373)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:381)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:344)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:221)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:537)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1081)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658)
    at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1580)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1537)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)

相同的代码在命令行程序中运行良好，所以我想我必须对 MQTT and/or tomcat 进行某种配置。我也不知道我是否需要额外的库。我只是将 paho 库复制到 WEB-INF 的 lib 文件夹中。

现在我只是在猜测可能是什么问题。

有人可以向我解释我必须如何配置 tomcat 或我必须将库移动到哪里吗？

非常感谢，

鲁迪

Answer 1

当 MQTT 客户端尝试打开持久性文件时抛出异常，我假设这可能是默认位置和用户的权限错误运行 Tomcat.

您可能需要通过传入 MQTTDefaultFilePersistence object to the MQTTClient() constructor after the client ID or pass in a MemoryPersistence 来设置路径，从而完全不需要存储到磁盘（如果 Tomcat 崩溃，这可能会丢失消息）。

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