Guava — Google Core Libraries for Java

Introduction

Guava is Google's open-source set of core Java libraries that supplement the standard library. It grew out of Google's internal Java codebase and provides battle-tested utilities used across thousands of production services.

What Guava Does

• Provides immutable collections (ImmutableList, ImmutableMap, ImmutableSet) that prevent accidental mutation
• Offers a powerful in-process caching API (LoadingCache, CacheBuilder) with size and time-based eviction
• Includes utilities for concurrency such as ListenableFuture and RateLimiter
• Supplies string utilities (Splitter, Joiner, CaseFormat) and precondition checks
• Adds functional-style helpers, hashing (Murmur3, SHA), I/O helpers, and math utilities

Architecture Overview

Guava is a single JAR of pure Java with zero transitive dependencies. It is organized into packages by domain: com.google.common.collect for collections, com.google.common.cache for caching, com.google.common.util.concurrent for concurrency, and so on. Each package is self-contained and follows Google's strict API compatibility guarantees.

Self-Hosting & Configuration

• Add the Maven or Gradle dependency; no external service required
• Choose the -jre artifact for Java 8+ or -android for Android and older JVMs
• Configure caching via CacheBuilder with maximumSize, expireAfterWrite, or expireAfterAccess
• Use @Beta-annotated APIs with caution as they may change between releases
• Guava follows semantic versioning; deprecated APIs are removed after a deprecation period

Key Features

• Immutable collections that are inherently thread-safe and memory-efficient
• LoadingCache with automatic loading, eviction policies, and statistics
• ListenableFuture and Futures utilities for composable async programming
• RateLimiter for smooth client-side rate limiting
• EventBus for lightweight publish-subscribe within a JVM process

Comparison with Similar Tools

• Apache Commons Lang — focuses on java.lang extensions; Guava covers a broader surface including collections and caching
• Eclipse Collections — richer primitive collections but lacks Guava's caching and concurrency utilities
• Caffeine — superior standalone cache (inspired by Guava Cache) but does not provide collections or I/O helpers
• Vavr — functional collections for Java; heavier API surface and learning curve

FAQ

Q: Is Guava still actively maintained? A: Yes. Google releases multiple updates per year and uses Guava extensively in production.

Q: Should I use Guava Cache or Caffeine? A: For new projects, Caffeine is recommended for pure caching. Guava Cache is adequate for existing codebases already depending on Guava.

Q: Does Guava work with Java 21+? A: Yes. The -jre artifact supports the latest LTS Java versions.

Q: What is the difference between -jre and -android artifacts? A: The -jre artifact targets Java 8+ and includes APIs using newer JDK types. The -android artifact avoids those for compatibility with Android and older runtimes.

Sources

• https://github.com/google/guava
• https://guava.dev/