square/okhttp

OkHttp is a library for making HTTP network requests from Java, Kotlin, and Android applications. HTTP is the protocol used to transfer data over the web, whenever your app fetches data from an API, downloads an image, or posts a form, it makes an HTTP request. The standard networking tools built into the Java and Android platforms work but have awkward APIs and lack many modern features. OkHttp provides a cleaner, more capable alternative. It is efficient by default in several important ways. It supports HTTP/2, a newer version of the protocol that allows multiple requests to the same server to share a single connection instead of opening a new one for each request, which significantly reduces latency. It uses connection pooling even for older HTTP/1.1 connections, automatically compresses responses using GZIP to reduce download sizes, and caches responses so repeat requests for the same data skip the network entirely. It handles real-world network reliability: if a server has multiple IP addresses (common for load-balanced services), OkHttp tries them in order on failure. It supports modern TLS security features including TLS 1.3 and certificate pinning. The API uses a builder pattern common in Java/Kotlin where you chain method calls to configure a request before sending it, and it supports both synchronous (blocking) and asynchronous (callback-based) request modes. You would use OkHttp in any Java or Kotlin application, including Android apps, that makes HTTP calls to web APIs, downloads files, or communicates with a backend server. It is the default HTTP client underlying many other popular Android libraries. It also includes a MockWebServer module for writing tests that simulate a real HTTP server without making actual network calls. The library is written in Kotlin and distributed via Maven Central.