Spring Cloud Stream

External

• https://cloud.spring.io/spring-cloud-stream/
• https://cloud.spring.io/spring-cloud-stream-app-starters/
• Reference Spring Cloud Stream Core https://docs.spring.io/spring-cloud-stream/docs/Elmhurst.RELEASE/reference/htmlsingle/#_spring_cloud_stream_core

Internal

• Spring Cloud

Overview

Spring Cloud Stream is a framework for building highly scalable event-driven microservices connected with shared messaging systems. Spring applications use Spring Cloud Stream libraries to bind to messaging middleware, using a middleware-specific-neutral API. The application uses input and output channel channel abstractions injected into it by Spring Cloud Stream runtime. Channels are connected to brokers through middleware-specific binder implementations.

Spring Cloud Stream builds upon Spring Boot to create standalone production-grade applications. Spring Initializr lists Spring Cloud Stream under "Cloud Messaging"

Concepts

Channel

An input channel is an object present in the memory of a Spring application whose implementation is transparently created by Spring Cloud Stream and injected int the application. The application uses input channel to receive messages. Similarly, an output channel is also an object created and injected by Spring Cloud Stream into the application. Application sends messages via output channels. The Spring Cloud Stream API conveniently provides factory interfaces for producing input channels (Sink), output channels (Source) and both (Processor).

Programming Model

The semantics of input, output and combined input/output channels is represented by the specialized interfaces:

public interface Sink {
  String INPUT = "input";

  @Input(Sink.INPUT)
  SubscribableChannel input();
}

public interface Source {
  String OUTPUT = "output";

  @Output(Source.OUTPUT)
  MessageChannel output();
}

public interface Processor extends Source, Sink {
}

Custom interfaces with the same semantics (factories of input and output channel instances.