Chapter 246. 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>

246.1. URI format

paho:topic[?options]

Where topic is the name of the topic.

246.2. Options

The Paho component supports 4 options which are listed below.

NameDescriptionDefaultType

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:

paho:topic

with the following path and query parameters:

246.2.1. Path Parameters (1 parameters):

NameDescriptionDefaultType

topic

Required Name of the topic

 

String

246.2.2. Query Parameters (14 parameters):

NameDescriptionDefaultType

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

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 options 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

246.3. Headers

The following headers are recognized by the Paho component:

HeaderJava constantEndpoint typeValue typeDescription

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

246.4. 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);

246.5. 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: 

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

And here we override the default topic and set to a dynamic topic

from("direct:test")
    .setHeader(PahoConstants.CAMEL_PAHO_OVERRIDE_TOPIC, simple("${header.customerId}"))
    .to("paho:some/target/queue");