JMS introduction and ActiveMQ actual code sharing

1、 Asynchronous communication

RMI, Hessian and other technologies previously contacted are synchronous communication mechanisms. When the client calls a remote method, the client must wait until the remote method is completed before continuing execution. During this time, the client will always be blocked (resulting in a poor user experience).

(synchronous communication)

Synchronous communication is not the only way to interact between programs. In asynchronous communication mechanism, the client does not need to wait for the service to process the message, can continue to execute, and can finally receive and process the message.

(asynchronous communication)

Advantages of asynchronous communication

No waiting. The client only needs to send the message to the message agent, can continue to perform other tasks without waiting, and is sure that the message will be delivered to the corresponding destination. Message oriented and decoupling. The client does not need to worry about the interface specification of the remote service. It only needs to put the message into the message queue and get the result.

2、 JMS

1. Introduction

Before the emergence of JMS, each message broker had different implementations, which made it difficult to generalize the message code between different brokers. JMS (Java Message Service) is a standard that defines a general API for using message broker. That is, all implementations that comply with the specification use a general interface, similar to JDBC, which provides a general interface for database operations.

There are several important elements of JMS:

Destination: the channel to go after the message is sent from the sender. Connectionfactory: connection factory, which is used to create connected objects. Connection: connection interface, used to create a session. Session: the session interface, which is used to create the sender and receiver of the message and the message object itself. Messageconsumer: the consumer of the message. Messageproducer: the producer of the message. Xxxmessage: various types of message objects, including bytemessage, mapmessage, objectmessage, streammessage and textmessage.

2. JMS message model

Different message systems have different message models. JMS provides two models: queue (point-to-point) and topic (publish / subscribe).

JMS queue model

In the point-to-point model, the message producer produces messages and sends them to the queue, and then the message consumer takes them out of the queue and consumes them, but they can not be consumed repeatedly.

As shown in the figure:

Sender 1, sender 2 and sender 3 send a message to the server respectively;

Messages 1, 2 and 3 will form a queue in order. The messages in the queue do not know which receiver they will be consumed by;

Recipients 1, 2 and 3 respectively take out a message from the queue for consumption. Each time they take out a message, the queue will delete the message, which ensures that the message will not be consumed repeatedly.

The JMS queue model has also become a P2P (point to point) model.

JMS topic (publish / subscribe) model

The biggest difference between the JMS topic model and the JMS queue model lies in the message receiving part. The official account of official account is similar to WeChat public number. Topic subscribers who subscribe to the official account can receive messages from the public.

As shown in the figure:

Publishers 1, 2 and 3 publish three topics 1, 2 and 3 respectively; In this way, the user group subscribed to topic 1: subscribers 1, 2 and 3 can receive topic 1 messages; Similarly, subscribers 4, 5 and 6 can receive topic 2 messages, and subscribers 7, 8 and 9 can receive topic 3 messages.

The JMS topic model also becomes the pus / sub model.

Comparison of elements under the two modes:

3. Traditional JMS programming model

Producer：

(1) Create a connection factory connectionfactory; (2) use a connection factory to create a connection; (3) start a connection; (4) create a session; (5) create a destination for message sending; (6) create a producer; (7) create a message type and message content; (8) send a message;

Consumer：

(1) Create a connection factory connectionfactory; (2) use a connection factory to create a connection; (3) start a connection; (4) create a session; (5) create a destination for message sending; (6) create a consumer; (7) create a message type; (8) receive a message;

3、 Introduction to ActiveMQ

ActiveMQ is the most popular and powerful open source message bus produced by Apache. ActiveMQ is a fully supported JMS 1 1 and J2EE 1.4 specifications. Although the JMS specification has been issued for a long time, JMS still plays a special role in today's J2EE applications.

Main features of ActiveMQ:

Write clients in multiple languages and protocols. Languages: Java, C, C + +, c#, ruby, Perl, python, PHP. Application protocols: openwire, stomp, rest, WS notification, XMPP, AMQP fully support JMS1 1 and J2EE 1.4 specifications (persistence, XA messages, transactions) support spring. ActiveMQ can be easily embedded into systems using spring, and also supports spring 2 The feature of 0 has passed the test of common J2EE servers (such as Geronimo, JBoss 4, GlassFish and Weblogic). Through the configuration of JCA 1.5 resource adapters, ActiveMQ can be automatically deployed to any J2EE 1.4 compatible commercial server, supporting a variety of transport protocols: in VM, TCP, SSL, NiO, UDP, jgroups, JXTA supports high-speed message persistence through JDBC and journal. It is designed to ensure high-performance clusters, client server, point-to-point support, AJAX support and axis integration. It is easy to call the embedded JMS provider for testing

4、 ActiveMQ practice

Let's see how ActiveMQ implements a simple message queue.

Traditional JMS programming model

1. Code implementation of JMS queue model:

Producer：

Conusmer：

2. JMS topic model code implementation:

Producer：

Consumer：

Using spring's JMS template

Although JMS provides a unified interface for all message brokers, like JDBC, it is very complicated when dealing with connections, statements, result sets and exceptions. However, spring provides us with a jmtemplate to eliminate redundant and duplicate JMS code. Let's take a look at how to use jmtemplate to implement message queuing.

1. Code implementation of JMS queue model:

Configuration file: producer xml:

consumer. xml:

Producer:

(1) Write an interface first:

(2) Implementation of interface:

(3) Test:

consumer:

(1) To create a message listener:

(2) Test:

2. JMS topic model code implementation:

Change the queuedestination in the above code to topicdestination.

summary

The above is all about JMS introduction and ActiveMQ actual code sharing in this article. I hope it will be helpful to you. Interested friends can continue to refer to other related topics on this site. If there are deficiencies, please leave a message to point out. Thank you for your support!