Chapter 6. Messaging Channels

Abstract

Messaging channels provide the plumbing for a messaging application. This chapter describes the different kinds of messaging channels available in a messaging system, and the roles that they play.

6.1. Point-to-Point Channel

Overview

A point-to-point channel, shown in Figure 6.1, “Point to Point Channel Pattern” is a message channel that guarantees that only one receiver consumes any given message. This is in contrast with a publish-subscribe channel, which allows multiple receivers to consume the same message. In particular, with a point-to-point channel, it is possible for multiple receivers to subscribe to the same channel. If more than one receiver competes to consume a message, it is up to the message channel to ensure that only one receiver actually consumes the message.

Figure 6.1. Point to Point Channel Pattern

Point to point channel pattern

Components that support point-to-point channel

The following Apache Camel components support the point-to-point channel pattern:

JMS

In JMS, a point-to-point channel is represented by a queue. For example, you can specify the endpoint URI for a JMS queue called Foo.Bar as follows:
jms:queue:Foo.Bar
The qualifier, queue:, is optional, because the JMS component creates a queue endpoint by default. Therefore, you can also specify the following equivalent endpoint URI:
jms:Foo.Bar
See Jms in the Apache Camel Component Reference Guide for more details.

ActiveMQ

In ActiveMQ, a point-to-point channel is represented by a queue. For example, you can specify the endpoint URI for an ActiveMQ queue called Foo.Bar as follows:
activemq:queue:Foo.Bar
See ActiveMQ in the Apache Camel Component Reference Guide for more details.

SEDA

The Apache Camel Staged Event-Driven Architecture (SEDA) component is implemented using a blocking queue. Use the SEDA component if you want to create a lightweight point-to-point channel that is internal to the Apache Camel application. For example, you can specify an endpoint URI for a SEDA queue called SedaQueue as follows:
seda:SedaQueue

JPA

The Java Persistence API (JPA) component is an EJB 3 persistence standard that is used to write entity beans out to a database. See Jpa in the Apache Camel Component Reference Guide for more details.

XMPP

The XMPP (Jabber) component supports the point-to-point channel pattern when it is used in the person-to-person mode of communication. See Xmpp in the Apache Camel Component Reference Guide for more details.