JMS

[ythy]

API jms

Architecture

A JMS application is composed of the following parts:

• A JMS provider: A messaging system that implements the JMS specification.
• JMS clients: Java applications that send and receive messages.
• Messages: Objects that are used to communicate information between JMS clients.
• Administered objects: Preconfigured JMS objects that are created by an administrator for the use of JMS clients.

Message Delivery Models

JMS supports two different message delivery models:

• Point-to-Point (Queue destination): In this model, a message is delivered from a producer to one consumer. The messages are delivered to the destination, which is a queue, and then delivered to one of the consumers registered for the queue. While any number of producers can send messages to the queue, each message is guaranteed to be delivered, and consumed by one consumer. If no consumers are registered to consume the messages, the queue holds them until a consumer registers to consume them.
• Publish/Subscribe (Topic destination): In this model, a message is delivered from a producer to any number of consumers. Messages are delivered to the topic destination, and then to all active consumers who have subscribed to the topic. In addition, any number of producers can send messages to a topic destination, and each message can be delivered to any number of subscribers. If there are no consumers registered, the topic destination doesn't hold messages unless it has durable subscription for inactive consumers. A durable subscription represents a consumer registered with the topic destination that can be inactive at the time the messages are sent to the topic.

[ythy]

doSendAndReceive

/**
 * Send a request message to the given {@link Destination} and block until
 * a reply has been received on a temporary queue created on-the-fly.
 * <p>Return the response message or {@code null} if no message has
 * @throws JMSException if thrown by JMS API methods
 */

[ythy]

Two beans that you don’t see defined are JmsTemplate and ConnectionFactory. These are created automatically by Spring Boot. In this case, the ActiveMQ broker runs embedded.

2020-06-12 14:43:57.578  INFO 16856 --- [  restartedMain] o.apache.activemq.broker.BrokerService   : Apache ActiveMQ 5.15.6 (localhost, ID:IT-Maoxin-61635-1591944237436-0:1) is starting
2020-06-12 14:43:57.583  INFO 16856 --- [  restartedMain] o.apache.activemq.broker.BrokerService   : Apache ActiveMQ 5.15.6 (localhost, ID:IT-Maoxin-61635-1591944237436-0:1) started
2020-06-12 14:43:57.583  INFO 16856 --- [  restartedMain] o.apache.activemq.broker.BrokerService   : For help or more information please see: http://activemq.apache.org
2020-06-12 14:43:57.617  INFO 16856 --- [  restartedMain] o.a.activemq.broker.TransportConnector   : Connector vm://localhost started

[ythy]

Instances of the JmsTemplate class are thread-safe, once configured. This is important, because it means that you can configure a single instance of a JmsTemplate and then safely inject this shared reference into multiple collaborators.