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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.

URI format

paho:queueName[?options]

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");

You can append query options to the URI in the following format: ?option=value&option=value&... . For example this is how to read messages from the remote MQTT broker: 

from("paho:some/queue?brokerUrl=tcp://iot.eclipse.org:1883").
  to("mock:test");

Adding the component to the project

...

<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>

URI format

paho:queueName[?options]

You can append query options to the URI in the following format: ?option=value&option=value&... .

URI Options

Example

Assumed we have a java bean with the following annotations

public class Car {

    @NotNull
    private String manufacturer;

    @NotNull
    @Size(min = 5, max = 14, groups = OptionalChecks.class)
    private String licensePlate;
    
    // getter and setter
}

and an interface definition for our custom validation group

public interface OptionalChecks {
}

with the following Camel route, only the @NotNull constraints on the attributes manufacturer and licensePlate will be validated (Camel uses the default group javax.validation.groups.Default).

from("direct:start")
.to("bean-validator://x")
.to("mock:end")

If you want to check the constraints from the group OptionalChecks, you have to define the route like this

from("direct:start")
.to("bean-validator://x?group=OptionalChecks")
.to("mock:end")

If you want to check the constraints from both groups, you have to define a new interface first

@GroupSequence({Default.class, OptionalChecks.class})
public interface AllChecks {
}

and then your route definition should looks like this

from("direct:start")
.to("bean-validator://x?group=AllChecks")
.to("mock:end")

And if you have to provide your own message interpolator, traversable resolver and constraint validator factory, you have to write a route like this

<bean id="myMessageInterpolator" class="my.ConstraintValidatorFactory" />
<bean id="myTraversableResolver" class="my.TraversableResolver" />
<bean id="myConstraintValidatorFactory" class="my.ConstraintValidatorFactory" />

from("direct:start")
.to("bean-validator://x?group=AllChecks&messageInterpolator=#myMessageInterpolator
&traversableResolver=#myTraversableResolver&constraintValidatorFactory=#myConstraintValidatorFactory")
.to("mock:end")

It's also possible to describe your constraints as XML and not as Java annotations. In this case, you have to provide the file META-INF/validation.xml which could looks like this

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>

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);

URI Options

For example the convention-over-configuration approach used in Camel is really handy for the most of the situations, but sometimes you would like to have more fine-grained control over the MQTT client connection. To cover such situations just add the bean of type org.eclipse.paho.client.mqttv3.MqttConnectOptions to your Camel registry. For Spring applications that would means adding bean to your application context. The snippet below uses password-based authentication to connect to the MQTT broker:

@Bean
MqttConnectOptions connectOptions() {
  MqttConnectOptions connectOptions = new MqttConnectOptions();
  connectOptions.setUserName("henry");
  connectOptions.setPassword("secret".toCharArray());
  return connectOptions;
}

Headers

The following headers are recognized by the Paho component:

 and the constraints-car.xml file