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JGroups Component

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

Starting from the Camel 2.13.0, JGroups component has been moved from Camel Extra under the umbrella of the Apache Camel. If you are using Camel 2.13.0 or higher, please use the following POM entry instead.

<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

Headers

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

Starting from version 2.13.0 of Camel, 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

Starting from version 2.13.0 of Camel, 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.

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("jetty:http://localhost:8080/orders").routeId("masterRoute").autoStartup(false).to("jms:orders");