What is publish and subscribe

In software architecture, publish and subscribe is a messaging paradigm. The sender of a message does not send the message directly to a specific recipient, but divides the published message into different categories without knowing which Subscribers may exist. Likewise, subscribers can express interest in one or more categories and receive only messages of interest without knowing which publishers exist.

In software architecture, publish and subscribe is a messaging paradigm in which the sender of the message (called the publisher) does not send the message directly to a specific The recipient (called a subscriber). Instead, published messages are grouped into different categories without knowing which subscribers (if any) might exist. Likewise, subscribers can express interest in one or more categories and receive only messages of interest without knowing which publishers (if any) exist.

Publish/Subscribe is the sibling of the message queue paradigm and is usually part of a larger message-oriented middleware system. Most messaging systems support both a message queue model and a publish/subscribe model in their API, such as Java Message Service (JMS).

This mode provides greater network scalability and a more dynamic network topology, while also reducing the flexibility of structural modifications to publishers and published data.

Message filtering

In the publish/subscribe model, subscribers typically receive a subset of all published messages. The process of selecting messages to accept and process is called filtering. There are two common forms of filtering: topic-based and content-based.

In a topic-based system, messages are published to topics or named channels. Subscribers will receive all messages on the topics to which they subscribe, and all subscribers to the same topic will receive the same messages. The publisher is responsible for defining the message categories to which subscribers subscribe.

In a content-based system, subscribers define the conditions for the messages they are interested in. Only when the attributes or content of the message meet the conditions defined by the subscriber, the message will be delivered to the subscriber. Subscribers are responsible for classifying messages.

Some systems support a mixture of the two: publishers publish messages to topics, and subscribers register content-based subscriptions to one or more topics.

The above is the detailed content of What is publish and subscribe. For more information, please follow other related articles on the PHP Chinese website!