JGroups Component

Available as of Camel version 2.13

JGroups is a toolkit for reliable multicast communication. The jgroups: component provides exchange of messages between Camel infrastructure and JGroups clusters.

Maven users will need to add the following dependency to their pom.xml for this component.

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-jgroups</artifactId>
    <!-- use the same version as your Camel core version -->
    <version>x.y.z</version>
</dependency>

URI format

jgroups:clusterName[?options]

Where clusterName represents the name of the JGroups cluster the component should connect to.

Options

The JGroups component supports 4 options, which are listed below.

Name Description Default Type

channel (common)

Channel to use

JChannel

channelProperties (common)

Specifies configuration properties of the JChannel used by the endpoint.

String

enableViewMessages (consumer)

If set to true, the consumer endpoint will receive org.jgroups.View messages as well (not only org.jgroups.Message instances). By default only regular messages are consumed by the endpoint.

false

boolean

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 JGroups endpoint is configured using URI syntax:

jgroups:clusterName

with the following path and query parameters:

Path Parameters (1 parameters):

Name Description Default Type

clusterName

Required The name of the JGroups cluster the component should connect to.

String

Query Parameters (6 parameters):

Name Description Default Type

channelProperties (common)

Specifies configuration properties of the JChannel used by the endpoint.

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

enableViewMessages (consumer)

If set to true, the consumer endpoint will receive org.jgroups.View messages as well (not only org.jgroups.Message instances). By default only regular messages are consumed by the endpoint.

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

Spring Boot Auto-Configuration

When using Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-jgroups-starter</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

The component supports 9 options, which are listed below.

Name Description Default Type

camel.component.jgroups.channel

Channel to use. The option is a org.jgroups.JChannel type.

String

camel.component.jgroups.channel-properties

Specifies configuration properties of the JChannel used by the endpoint.

String

camel.component.jgroups.enable-view-messages

If set to true, the consumer endpoint will receive org.jgroups.View messages as well (not only org.jgroups.Message instances). By default only regular messages are consumed by the endpoint.

false

Boolean

camel.component.jgroups.enabled

Enable jgroups component

true

Boolean

camel.component.jgroups.lock.cluster.service.enabled

Sets if the jgroups lock cluster service should be enabled or not, default is false.

false

Boolean

camel.component.jgroups.lock.cluster.service.id

Cluster Service ID

String

camel.component.jgroups.lock.cluster.service.jgroups-cluster-name

JGroups Cluster name

String

camel.component.jgroups.lock.cluster.service.jgroups-config

JGrups configuration File name

String

camel.component.jgroups.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

Headers

Header Constant Description

JGROUPS_ORIGINAL_MESSAGE

JGroupsEndpoint.HEADER_JGROUPS_ORIGINAL_MESSAGE

The original org.jgroups.Message instance from which the body of the consumed message has been extracted.

JGROUPS_SRC

`JGroupsEndpoint.`HEADER_JGROUPS_SRC

Consumer : The org.jgroups.Address instance extracted by org.jgroups.Message.getSrc() method of the consumed message. Producer: The custom source org.jgroups.Address of the message to be sent.

JGROUPS_DEST

`JGroupsEndpoint.`HEADER_JGROUPS_DEST

Consumer: The org.jgroups.Address instance extracted by org.jgroups.Message.getDest() method of the consumed message. Producer: The custom destination org.jgroups.Address of the message to be sent.

JGROUPS_CHANNEL_ADDRESS

`JGroupsEndpoint.`HEADER_JGROUPS_CHANNEL_ADDRESS

Address (org.jgroups.Address) of the channel associated with the endpoint.

Usage

Using jgroups component on the consumer side of the route will capture messages received by the JChannel associated with the endpoint and forward them to the Camel route. JGroups consumer processes incoming messages asynchronously.

// Capture messages from cluster named
// 'clusterName' and send them to Camel route.
from("jgroups:clusterName").to("seda:queue");

Using jgroups component on the producer side of the route will forward body of the Camel exchanges to the JChannel instance managed by the endpoint.

// Send message to the cluster named 'clusterName'
from("direct:start").to("jgroups:clusterName");

Predefined filters

JGroups component comes with predefined filters factory class named JGroupsFilters.

If you would like to consume only view changes notifications sent to coordinator of the cluster (and ignore these sent to the "slave" nodes), use the JGroupsFilters.dropNonCoordinatorViews() filter. This filter is particularly useful when you want a single Camel node to become the master in the cluster, because messages passing this filter notifies you when given node has become a coordinator of the cluster. The snippet below demonstrates how to collect only messages received by the master node.

import static org.apache.camel.component.jgroups.JGroupsFilters.dropNonCoordinatorViews;
...
from("jgroups:clusterName?enableViewMessages=true").
  filter(dropNonCoordinatorViews()).
  to("seda:masterNodeEventsQueue");

Predefined expressions

JGroups component comes with predefined expressions factory class named JGroupsExpressions.

If you would like to create delayer that would affect the route only if the Camel context has not been started yet, use the JGroupsExpressions.delayIfContextNotStarted(long delay) factory method. The expression created by this factory method will return given delay value only if the Camel context is in the state different than started. This expression is particularly useful if you would like to use JGroups component for keeping singleton (master) route within the cluster. Control Bus start command won’t initialize the singleton route if the Camel Context hasn’t been yet started. So you need to delay a startup of the master route, to be sure that it has been initialized after the Camel Context startup. Because such scenario can happen only during the initialization of the cluster, we don’t want to delay startup of the slave node becoming the new master - that’s why we need a conditional delay expression.

The snippet below demonstrates how to use conditional delaying with the JGroups component to delay the initial startup of master node in the cluster.

import static java.util.concurrent.TimeUnit.SECONDS;
import static org.apache.camel.component.jgroups.JGroupsExpressions.delayIfContextNotStarted;
import static org.apache.camel.component.jgroups.JGroupsFilters.dropNonCoordinatorViews;
...
from("jgroups:clusterName?enableViewMessages=true").
  filter(dropNonCoordinatorViews()).
  threads().delay(delayIfContextNotStarted(SECONDS.toMillis(5))). // run in separated and delayed thread. Delay only if the context hasn't been started already.
  to("controlbus:route?routeId=masterRoute&action=start&async=true");

from("timer://master?repeatCount=1").routeId("masterRoute").autoStartup(false).to(masterMockUri);

Examples

Sending (receiving) messages to (from) the JGroups cluster

In order to send message to the JGroups cluster use producer endpoint, just as demonstrated on the snippet below.

from("direct:start").to("jgroups:myCluster");
...
producerTemplate.sendBody("direct:start", "msg")

To receive the message from the snippet above (on the same or the other physical machine) listen on the messages coming from the given cluster, just as demonstrated on the code fragment below.

mockEndpoint.setExpectedMessageCount(1);
mockEndpoint.message(0).body().isEqualTo("msg");
...
from("jgroups:myCluster").to("mock:messagesFromTheCluster");
...
mockEndpoint.assertIsSatisfied();

Receive cluster view change notifications

The snippet below demonstrates how to create the consumer endpoint listening to the notifications regarding cluster membership changes. By default only regular messages are consumed by the endpoint.

mockEndpoint.setExpectedMessageCount(1);
mockEndpoint.message(0).body().isInstanceOf(org.jgroups.View.class);
...
from("jgroups:clusterName?enableViewMessages=true").to(mockEndpoint);
...
mockEndpoint.assertIsSatisfied();

Keeping singleton route within the cluster

The snippet below demonstrates how to keep the singleton consumer route in the cluster of Camel Contexts. As soon as the master node dies, one of the slaves will be elected as a new master and started. In this particular example we want to keep singleton jetty instance listening for the requests on address` http://localhost:8080/orders`.

JGroupsLockClusterService service = new JGroupsLockClusterService();
service.setId("uniqueNodeId");
...
context.addService(service);

from("master:mycluster:jetty:http://localhost:8080/orders").to("jms:orders");