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
• spring-webflux is a whole new non-blocking API for Spring

Spring Reactive Types

• Mono - A publisher with 0 or 1 elements in datastream
• Flux - A publisher with 0+ elements in datastream