Before reading this post, please go through my previous at “JMS Messaging Models” to understand some JMS Basic concepts.
In this post we are going to discuss about JMS Administered Objects and JMS Message in detail.
Post Brief TOC:
- JMS Administered Objects
- JMS Message
- Message Header
- Message Properties
- Message Body
JMS Administered Objects
JMS API provides two kinds of Administered Objects to the JMS Clients.
- Connection Factory
- Destination
JMS System Administrator creates these two Administered objects in JMS Provider (Message Broker) by using Application Server (AS) admin console. These two objects are stored in AS JNDI Directory or JNDI Registry.
Destination
Destination object is used to exchange messages between JMS Clients. JMS API provides two kinds of Destinations:
Connection Factory
Connection Factory object is used to create connection between JMS Provider and JMS Client. When JMS Client (JMS Sender or JMS Receiver) lookups this object from JNDI Registry, then JMS Client receives one Connection object that is nothing but a physical connection between JMS Provider and JMS Client. By using this connection, JMS Client can communicate with Destination object to send or receive messages into Queue or Topic.
While creating these two objects, we need to provide three things
- Name :- Name of the object. We can provide any valid name
- JNDI Name:- This is JNDI name which is used to register this object in JNDI Directory. JMS Clients uses this name to lookup these objects from JNDI Registry and use them in their applications to send or receive messages from JMS Provider.
- Resource Type:- We need to specify the resource type here.
Example:-
To create a Queue Object in Oracle GlassFish Application Server
Here I’ve provided Destination Name = TPQueue , JNDI Name = jms/TPQueue and Resource Type as javax.jms.Queue. JMS Clients can lookup this object by using the following code snippet:
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Queue queue = (Queue) context.lookup("jms/TPQueue"); |
JMS Message
JMS Messages are used by JMS clients to exchange information between systems. This JMS Message is of type javax.jms.Message.
This JMS Message is divided into 3 parts:
- Message Header
- Message Properties
- Message Body
This section is mandatory. It contains predefined name-value pairs used by JMS Clients and JMS Providers to identify and route messages.
Predefined Headers:
- JMSDestination
- JMSDeliveryMode
- JMSMessageID
- JMSTimestamp
- JMSCorrelationID
- JMSReplyTo
- JMSRedelivered
- JMSType
- JMSExpiration
- JMSPriority
Message Properties
This section is optional. These properties are custom name-value pairs set or read by applications. These are useful for supporting filtering messages. We will discuss it in detail in Messaging Filtering Advanced JMS Concepts section.
Message Body
This section is optional. It contains actual message sent from JMS Sender to JMS Receiver.
It supports the following message formats:
- TextMessage
- ObjectMessage
- BytesMessage
- StreamMessage
- MapMessage
These JMS message types are described in the following table:
That’s it all about JMS Administered Objects and JMS Message. We will discuss some more JMS Concepts in my coming posts.
Please drop me a comment if you like my post or have any issues/suggestions.