feign

Feign is a Java to HTTP client binder that enables developers to create declarative REST clients. With Feign, a programmer defines a Java interface where methods represent remote HTTP calls, and annotations specify the HTTP method, path, headers, and parameters. Feign generates a concrete implementation at runtime that performs the actual network requests and maps responses to Java types.

Key features include pluggable encoders and decoders for request and response bodies (for example JSON via Jackson or Gson), and pluggable HTTP client implementations such as OkHttp, Apache HttpClient, or the JDK’s HttpURLConnection. Feign also supports request interceptors, retry behavior, and customizable error handling. Its contracts allow flexibility in how annotations are interpreted, and it can be extended with custom error decoders and metrics.

In microservice architectures, Feign is often used with client-side load balancing and service discovery. It can integrate with Ribbon for load balancing and with Eureka or other registries for discovery. Spring Cloud provides integration through Spring Cloud OpenFeign, offering Spring-friendly annotations and auto-configuration. Feign can also be paired with circuit breakers and resilience libraries such as Hystrix or resilience4j to supply fallback logic.

History and status: Feign was developed by Netflix as part of its open source microservices ecosystem and was released for general use. Over time, community-driven forks and integrations—such as OpenFeign and Spring Cloud OpenFeign—have continued to evolve Feign’s API and ecosystem, maintaining its role as a lightweight, declarative HTTP client for Java.