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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
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 chapter "JMS" in "Apache Camel Component Reference" 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 chapter "ActiveMQ" in "Apache Camel Component Reference" 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 chapter "JPA" in "Apache Camel Component Reference" 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 chapter "XMPP" in "Apache Camel Component Reference" for more details.
