Chapter 259. Paho Component Available as of Camel version 2.16 Paho component provides connector for the MQTT messaging protocol using the Eclipse Paho library. Paho is one of the most popular MQTT libraries, so if you would like to integrate it with your Java project - Camel Paho connector is a way to go. Maven users will need to add the following dependency to their pom.xml for this component: <dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-paho</artifactId> <version>x.y.z</version> <!-- use the same version as your Camel core version --> </dependency> Keep in mind that Paho artifacts are not hosted in the Maven Central, so you need to add Eclipse Paho repository to your POM xml file: <repositories> <repository> <id>eclipse-paho</id> <url>https://repo.eclipse.org/content/repositories/paho-releases</url> <snapshots> <enabled>false</enabled> </snapshots> </repository> </repositories> 259.1. URI format Where topic is the name of the topic. 259.2. Options The Paho component supports 4 options, which are listed below. Name Description Default Type brokerUrl (common) The URL of the MQTT broker. String clientId (common) MQTT client identifier. String connectOptions (advanced) Client connection options MqttConnectOptions resolveProperty Placeholders (advanced) Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders. true boolean The Paho endpoint is configured using URI syntax: with the following path and query parameters: 259.2.1. Path Parameters (1 parameters): Name Description Default Type topic Required Name of the topic String 259.2.2. Query Parameters (15 parameters): Name Description Default Type autoReconnect (common) Client will automatically attempt to reconnect to the server if the connection is lost true boolean brokerUrl (common) The URL of the MQTT broker. tcp://localhost:1883 String clientId (common) MQTT client identifier. String connectOptions (common) Client connection options MqttConnectOptions filePersistenceDirectory (common) Base directory used by the file persistence provider. String password (common) Password to be used for authentication against the MQTT broker String persistence (common) Client persistence to be used - memory or file. MEMORY PahoPersistence qos (common) Client quality of service level (0-2). 2 int resolveMqttConnectOptions (common) Define if you don't want to resolve the MQTT Connect Options from registry true boolean retained (common) Retain option false boolean userName (common) Username to be used for authentication against the MQTT broker String bridgeErrorHandler (consumer) Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. false boolean exceptionHandler (consumer) To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored. ExceptionHandler exchangePattern (consumer) Sets the exchange pattern when the consumer creates an exchange. ExchangePattern synchronous (advanced) Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported). false boolean 259.3. Spring Boot Auto-Configuration The component supports 5 options, which are listed below. Name Description Default Type camel.component.paho.broker-url The URL of the MQTT broker. String camel.component.paho.client-id MQTT client identifier. String camel.component.paho.connect-options Client connection options. The option is a org.eclipse.paho.client.mqttv3.MqttConnectOptions type. String camel.component.paho.enabled Enable paho component true Boolean camel.component.paho.resolve-property-placeholders Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders. true Boolean 259.4. Headers The following headers are recognized by the Paho component: Header Java constant Endpoint type Value type Description CamelMqttTopic PahoConstants.MQTT_TOPIC Consumer String The name of the topic CamelPahoOverrideTopic PahoConstants.CAMEL_PAHO_OVERRIDE_TOPIC Producer String Name of topic to override and send to instead of topic specified on endpoint 259.5. Default payload type By default Camel Paho component operates on the binary payloads extracted out of (or put into) the MQTT message: // Receive payload byte[] payload = (byte[]) consumerTemplate.receiveBody("paho:topic"); // Send payload byte[] payload = "message".getBytes(); producerTemplate.sendBody("paho:topic", payload); But of course Camel build-in type conversion API can perform the automatic data type transformations for you. In the example below Camel automatically converts binary payload into String (and conversely): // Receive payload String payload = consumerTemplate.receiveBody("paho:topic", String.class); // Send payload String payload = "message"; producerTemplate.sendBody("paho:topic", payload); 259.6. Samples For example the following snippet reads messages from the MQTT broker installed on the same host as the Camel router: from("paho:some/queue") .to("mock:test"); While the snippet below sends message to the MQTT broker: from("direct:test") .to("paho:some/target/queue"); For example this is how to read messages from the remote MQTT broker: And here we override the default topic and set to a dynamic topic from("direct:test") .setHeader(PahoConstants.CAMEL_PAHO_OVERRIDE_TOPIC, simple("USD{header.customerId}")) .to("paho:some/target/queue");

Commands:
<dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-paho</artifactId> <version>x.y.z</version> <!-- use the same version as your Camel core version --> </dependency>
<repositories> <repository> <id>eclipse-paho</id> <url>https://repo.eclipse.org/content/repositories/paho-releases</url> <snapshots> <enabled>false</enabled> </snapshots> </repository> </repositories>
paho:topic[?options]
paho:topic
// Receive payload byte[] payload = (byte[]) consumerTemplate.receiveBody("paho:topic"); // Send payload byte[] payload = "message".getBytes(); producerTemplate.sendBody("paho:topic", payload);
// Receive payload String payload = consumerTemplate.receiveBody("paho:topic", String.class); // Send payload String payload = "message"; producerTemplate.sendBody("paho:topic", payload);
from("paho:some/queue") .to("mock:test");
from("direct:test") .to("paho:some/target/queue");
from("paho:some/queue?brokerUrl=tcp://iot.eclipse.org:1883") .to("mock:test");
from("direct:test") .setHeader(PahoConstants.CAMEL_PAHO_OVERRIDE_TOPIC, simple("USD{header.customerId}")) .to("paho:some/target/queue");