My current understanding is that both of these projects are under Spring Cloud Dataflow, and serve as components of the pipeline. However, both can be made recurring (a stream is by definition recurring, where a task can run every certain time interval). In addition, both can be configured to communicate with the rest of the pipeline through the message broker. Currently there is this unanswered question, so I've yet to find a clear answer.
Please see my response as below:
My current understanding is that both of these projects are under Spring Cloud Dataflow, and serve as components of the pipeline.
Both Spring Cloud Stream and Spring Cloud Task are not under Spring Cloud Data Flow, instead, they can be used as standalone projects and Spring Cloud Data Flow just uses them.
Spring Cloud Stream lets you bind your event-driven long-running applications into a messaging middleware or a streaming platform. As a developer, you have to choose your binder (the binder implementations for RabbitMQ, Apache Kafka etc.,) to stream your events or data from/to the messaging middleware you bind to.
Spring Cloud Task doesn't bind your application into a messaging middleware. Instead, it provides abstractions and lifecycle management to run your ephemeral or finite duration applications (tasks). It also provides the foundation for developing Spring Batch applications.
However, both can be made recurring (a stream is by definition recurring, where a task can run every certain time interval)
A task application can be triggered/scheduled to make it a recurring one whereas the streaming application is a long-running, not a recurring one.
In addition, both can be configured to communicate with the rest of the pipeline through the message broker.
Though a task application can be configured to communicate to a messaging middleware, the concept of pipeline is different when it comes to stream vs task (batch). For the streaming applications, the pipeline refers to the communication via the messaging middleware while for the task applications, the concept of composed tasks lets you create a conditional workflow of multiple task applications. For more information on composed tasks, you can refer to the documentation.