Processor: Dual Role in Reactive Streams

A processor in a reactive stream is a special component that acts as both a subscriber to one stream and a publisher to another. This dual role allows it to sit in the middle of a data flow, transforming or filtering data as it passes through.

How a Processor Works

1. Receives data from an upstream publisher as a subscriber;
2. Processes, transforms, or filters the incoming data;
3. Publishes the processed data to downstream subscribers.

This makes the processor a bridge between the source of data and the consumers. You can chain multiple processors to build complex data pipelines, each step handling part of the processing.

Flow and Interaction

• When a publisher emits data, the processor receives it using the onNext method as a subscriber.
• The processor can apply logic such as mapping, filtering, or batching to the data.
• After processing, the processor emits the new data to its own subscribers using onNext as a publisher.
• The processor also handles signals like onError and onComplete from upstream and passes them downstream.

This pattern ensures that each stage of the data flow remains reactive, handling backpressure and errors efficiently. The processor’s dual nature allows you to modularize and compose complex data processing tasks in a clear, maintainable way.