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This article mainly explains "how to use redis publish and subscribe to achieve a simple message system", the content of the article is simple and clear, easy to learn and understand, the following please follow the editor's ideas slowly in depth, together to study and learn "how to use redis publish and subscribe to achieve a simple message system"!

i. Basically use 1. Configuration

We use SpringBoot 2.2.1.RELEASE to build the project environment and add redis dependencies directly to pom.xml

Org.springframework.boot spring-boot-starter-data-redis

If our redis is the default configuration, no additional configuration can be added, or directly in the application.yml configuration, as follows

Spring: redis: host: 127.0.0.1 port: 6379 password:2. Use posture

The publish / subscribe of redis mainly uses two commands, publish/subscribe;, to use publish / subscribe mode in SpringBoot is relatively simple, and it can be easily realized with RedisTemplate.

a. News release @ Servicepublic class PubSubBean {@ Autowired private StringRedisTemplate redisTemplate; public void publish (String key, String value) {redisTemplate.execute (new RedisCallback () {@ Override public Object doInRedis (RedisConnection redisConnection) throws DataAccessException {redisConnection.publish (key.getBytes (), value.getBytes (); return null;}});}} b. Subscribe to messages

Message subscription here, we need to note that we use org.springframework.data.redis.connection.MessageListener to implement the consumption logic.

Public void subscribe (MessageListener messageListener, String key) {redisTemplate.execute (new RedisCallback () {@ Override public Object doInRedis (RedisConnection redisConnection) throws DataAccessException {redisConnection.subscribe (messageListener, key.getBytes (); return null;}});} c. Test case

Write a simple test case to verify the publication subscription above and understand the posture of using this MessageListener by the way; let's create a simple WEB project that provides two rest interfaces

@ RestController@RequestMapping (path = "rest") public class DemoRest {@ Autowired private PubSubBean pubSubBean; / / publish message @ GetMapping (path = "pub") public String pubTest (String key, String value) {pubSubBean.publish (key, value); return "over" } / / New consumers @ GetMapping (path = "sub") public String subscribe (String key, String uuid) {pubSubBean.subscribe (new MessageListener () {@ Override public void onMessage (Message message, byte [] bytes) {System.out.println (uuid + "= > msg:" + message);}, key); return "over" }}

We first create two consumers, and then when we send a message, we receive both; then we add a new consumer, and when we send a message, we receive all three.

3. Usage instructions and application scenarios

Redis publish and subscribe is only suitable for relatively simple scenarios. As can be seen from the instructions above, it is a simple publish and subscribe model, which supports 1 to N, and sends messages that only online consumers can get (as for those that are not online, it can only be said to be regrettable). And for redis, the message is finished after the message is pushed out, and as to whether consumers can consume normally, it will not be care.

Highlight:

Only online consumers can receive messages.

For consumers, you can only get a message once.

The next question is, what kind of scenario can you use redis's publish and subscribe?

Memory-based cache invalidation

Using reids + memory to do secondary cache can be said to be a common way. With the help of memory-based cache, it can effectively increase the load of the system, but the problem is also obvious. The failure of cached data in memory is a problem, especially when an application deploys multiple servers. If I want to invalidate a certain memory cache of all servers at the same time, using redis publish / subscribe is a better choice.

SpringCloud Config configuration refresh

Partners who use SpringCloud Config as the configuration center may often encounter this problem. Dynamic refresh after configuration modification is a problem (of course, it is officially supported to synchronize through mq via bus bus, or you can use spring boot admin to strongly refresh).

With the help of redis publish / subscribe, dynamic refresh of configuration is also a good alternative (a specific implementation demo is given later. If you are interested, please continue to follow a gray Blog)

Redis key invalid subscription

When we use redis for caching, we usually set an expiration time. Redis provides an expired event, which is not enabled by default. We can also subscribe to cache invalidation events through subscribe.

Modify the configuration to enable key failure events

Notify-keyspace-events Ex

After restarting redis, subscribe to invalidation events.

Subscribe _ _ keyevent@0__:expired thank you for your reading, the above is the content of "how to use redis publish and subscribe to achieve a simple message system". After the study of this article, I believe you have a deeper understanding of how to use redis publish and subscribe to achieve a simple message system, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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