Key concepts and components of Java Reactive Programming include:

1. Reactive Streams API: The Reactive Streams API is a standard for asynchronous stream processing in Java. It provides a set of interfaces (e.g., Publisher, Subscriber, Subscription, Processor) that allow developers to create, consume, and manipulate streams of data asynchronously and non-blocking.

2. Publishers: Publishers are sources of data streams. They produce data items and push them to subscribers when the data is available. In Java, publishers are often implemented using libraries like Project Reactor and RxJava.

3. Subscribers: Subscribers are consumers of data streams. They subscribe to publishers to receive data items asynchronously. Subscribers define how to process and react to incoming data.

4. Operators: Operators are functions or methods that allow developers to transform, filter, combine, or otherwise manipulate data streams. Operators are a fundamental part of reactive programming and enable complex data processing pipelines.

5. Backpressure Handling: Reactive programming systems include mechanisms for handling backpressure, which occurs when subscribers cannot keep up with the rate of data emission from publishers. Backpressure strategies include buffering, dropping, or requesting data at a slower rate.

6. Schedulers: Schedulers are used to control the execution context in which reactive code runs. They allow developers to specify whether code should run on the main thread, a separate thread, or a thread pool.

7. Reactive Libraries: Several Java libraries and frameworks support reactive programming, including Project Reactor, RxJava, Akka Streams, and Vert.x. These libraries provide implementations of the Reactive Streams API and additional tools for building reactive systems.

8. Reactive Web Frameworks: Some web frameworks, like Spring WebFlux, are designed with reactive programming principles in mind. They allow developers to build web applications that can handle a large number of concurrent requests using reactive streams.

9. Reactive Database Access: Reactive programming can extend to database access with libraries like R2DBC (Reactive Relational Database Connectivity) for interacting with relational databases in a reactive manner.

10. Reactive Systems: Reactive programming is often used to build reactive systems that are responsive to changes in the environment, resilient in the face of failures, and can scale horizontally as needed. These systems are well-suited for microservices architectures and cloud-native applications.