# Reactive Programming

Reactive programming focuses on non-blocking, asynchronous execution
## The Reactive Manifesto

### Responsive
- The System responds in a timely manner
- Responsiveness is the cornerstone of usability and utility
- Reponsiveness also means problems may be detected quickly
- Responsive systems provide rapid and consistent response times
- Consistent behavior simplifies error handling, builds end user confidence, and encourages further interaction

### Resilient
- System stays responsive in the face of failure
- Resilience is achieved by replication, containment, isolation, and delegation
- Failures are contianed within each component
- Parts of the system can fail, without compromising the system as a whole
- Recovery of each component is delegated to another
- High-availability is ensured by replication where necessary

### Elastic
- The System stays responsive under varying workload
- Reactive Systems can react to changes in the input rate by changing the amount of resources allocated to service inputs
- Reactive Systems achieve elaticity in a cost effective way on commodity hardware and software platforms

### Message Driven
- Reactive Systems rely on asynchronous message passing to establish a boundary between components
	- This ensures loose coupling, isolation, and location transparency
- Message passing enables load management, elasticity and flow control
- Location transparent messaging makes management of failures possible
- Non-blocking communication allows recipients to only consume resources while active leading to less system overhead


## Features of Reactive Programming
- Data Streams
- Asyncronous
- Non-blocking - Process what is availble and ask for a notificaiton when more is available
- Backpressure - The ability of the client to throttle data
- Failures as Messages - Exceptions are processed by a handler function

## Reactive Streams
- Reactive Streams API was started in 2013 by engineers from Netflix and other companies. It was officially released 2015 and is now part of Java 9 JDK
[![![92834787bd1f2632805a67e158738e69.png](:/11a26d2ed13c48bbb4f9072d71dd50ad)](https://bookstack.mitchellhenschel.com/uploads/images/gallery/2022-04/scaled-1680-/image-1650156073797.png)](https://bookstack.mitchellhenschel.com/uploads/images/gallery/2022-04/image-1650156073797.png)
- spring-webflux is a whole new non-blocking API for Spring
[![![4702ef7341bfe8112eff9b0c8e55221e.png](:/57185a32c6344f6aa278efbd187980b4)](https://bookstack.mitchellhenschel.com/uploads/images/gallery/2022-04/scaled-1680-/image-1650156080115.png)](https://bookstack.mitchellhenschel.com/uploads/images/gallery/2022-04/image-1650156080115.png)

### Spring Reactive Types
- Mono - A publisher with 0 or 1 elements in datastream
- Flux - A publisher with 0+ elements in datastream