dOOv - Provides fluent API for typesafe domain model validation and mapping. It uses annotations, code generation and a type safe DSL to make bean validation and mapping fast and easy.
JMapper - Uses byte code manipulation for lightning-fast mapping. Supports annotations and API or XML configuration.
MapStruct - Code generator that simplifies mappings between different bean types, based on a convention-over-configuration approach.
ModelMapper - Intelligent object mapping library that automatically maps objects to each other.
Orika - JavaBean-mapping framework that recursively copies (among other capabilities) data from one object to another.
reMap - Lambda and method handle-based mapping which requires code and not annotations if objects have different names.
Tools that handle the build cycle and dependencies of an application.
Apache Maven - Declarative build and dependency management that favors convention over configuration. It might be preferable to Apache Ant, which uses a rather procedural approach and can be difficult to maintain.
Bazel - Tool from Google that builds code quickly and reliably.
Buck - Encourages the creation of small, reusable modules consisting of code and resources.
Gradle - Incremental builds programmed via Groovy instead of declaring XML. Works well with Maven's dependency management.
Bytecode Manipulation
Libraries to manipulate bytecode programmatically.
ASM - All-purpose, low-level bytecode manipulation and analysis.
Byte Buddy - Further simplifies bytecode generation with a fluent API.
Jexer - Advanced console (and Swing) text user interface (TUI) library, with mouse-draggable windows, built-in terminal window manager, and sixel image support. Looks like Turbo Vision.
JLine - Includes features from modern shells like completion or history.
JOpt Simple - Fluent parser that uses the POSIX#getopt and GNU#getopt_long syntaxes.
picocli - ANSI colors and styles in usage help with annotation-based POSIX/GNU/any syntax, subcommands, strong typing for both options and positional args.
Text-IO - Aids the creation of full console-based applications.
Lanterna - Easy console text-GUI library, similar to curses. (LGPL-3.0-only)
Cluster Management
Frameworks that can dynamically manage applications inside of a cluster.
Apache Aurora - Mesos framework for long-running services and cron jobs.
Singularity - Mesos framework that makes deployment and operations easy. It supports web services, background workers, scheduled jobs, and one-off tasks.
Code Analysis
Tools that provide metrics and quality measurements.
Checkstyle - Static analysis of coding conventions and standards. (LGPL-2.1-or-later)
Error Prone - Catches common programming mistakes as compile-time errors.
Infer - Modern static analysis tool for verifying the correctness of code.
jQAssistant - Static code analysis with Neo4J-based query language. (GPL-3.0-only)
NullAway - Eliminates NullPointerExceptions with low build-time overhead.
PMD - Source code analysis for finding bad coding practices.
SonarJava - Static analyzer for SonarQube & SonarLint. (LGPL-3.0-only)
Spoon - Library for analyzing and transforming Java source code.
Spotbugs - Static analysis of bytecode to find potential bugs. (LGPL-2.1-only)
Code Coverage
Frameworks and tools that enable code coverage metrics collection for test suites.
Clover - Relies on source-code instrumentation instead of bytecode instrumentation.
Cobertura - Relies on offline (or static) bytecode instrumentation and class loading to collect code coverage metrics. (GPL-2.0-only)
JaCoCo - Framework that enables collection of code coverage metrics, using both offline and runtime bytecode instrumentation.
Code Generators
Tools that generate patterns for repetitive code in order to reduce verbosity and error-proneness.
ADT4J - JSR-269 code generator for algebraic data types.
Auto - Generates factory, service, and value classes.
Bootify - Browser-based Spring Boot app generation with JPA model and REST API.
FreeBuilder - Automatically generates the Builder pattern.
Geci - Discovers files that need generated code, updates automatically and writes to the source with a convenient API.
Immutables - Annotation processors to generate simple, safe and consistent value objects.
JHipster - Yeoman source code generator for Spring Boot and AngularJS.
Joda-Beans - Small framework that adds queryable properties to Java, enhancing JavaBeans.
JPA Buddy - Plugin for IntelliJ IDEA. Provides visual tools for generating JPA entities, Spring Data JPA repositories, Liquibase changelogs and SQL scripts. Offers automatic Liquibase/Flyway script generation by comparing model to DB, and reverse engineering JPA entities from DB tables.
Lombok - Code generator that aims to reduce verbosity.
Record-Builder - Companion builder class, withers and templates for Java records.
Telosys - Simple and light code generator available as an Eclipse Plugin and also as a CLI.
Compiler-compiler
Frameworks that help to create parsers, interpreters or compilers.
ANTLR - Complex full-featured framework for top-down parsing.
JavaCC - Parser generator that generates top-down parsers. Allows lexical state switching and permits extended BNF specifications.
Libraries which seek to gain high level information from images and videos.
BoofCV - Library for image processing, camera calibration, tracking, SFM, MVS, 3D vision, QR Code and much more.
ImageJ - Medical image processing application with an API.
JavaCV - Java interface to OpenCV, FFmpeg, and much more.
Configuration
Libraries that provide external configuration.
centraldogma - Highly-available version-controlled service configuration repository based on Git, ZooKeeper and HTTP/2.
cfg4j - Modern configuration library for distributed apps written in Java.
config - Configuration library supporting Java properties, JSON or its human optimized superset HOCON.
Configurate - Configuration library with support for various configuration formats and transformations.
dotenv - Twelve-factor configuration library which uses environment-specific files.
Externalized Properties - Lightweight but powerful configuration library which supports resolution of properties from external sources and an extensible post-processing/conversion mechanism.
ini4j - Provides an API for handling Windows' INI files.
KAConf - Annotation-based configuration system for Java and Kotlin.
microconfig - Configuration system designed for microservices which helps to separate configuration from code. The configuration for different services can have common and specific parts and can be dynamically distributed.
QueryStream - Build JPA Criteria queries using a Stream-like API.
QuestDB - High-performance SQL database for time series. Supports InfluxDB line protocol, PostgreSQL wire protocol, and REST.
Realm - Mobile database to run directly inside phones, tablets or wearables.
Redisson - Allows for distributed and scalable data structures on top of a Redis server.
requery - Modern, lightweight but powerful object mapping and SQL generator. Easily map to or create databases, or perform queries and updates from any Java-using platform.
Speedment - Database access library that utilizes Java 8's Stream API for querying.
DCEVM - JVM modification that allows unlimited redefinition of loaded classes at runtime. (GPL-2.0-only)
Faux Pas - Library that simplifies error handling by circumventing the issue that none of the functional interfaces in the Java Runtime is allowed by default to throw checked exceptions.
HotswapAgent - Unlimited runtime class and resource redefinition. (GPL-2.0-only)
JavaParser - Parse, modify and generate Java code.
ScaleCube Services - Embeddable Cluster-Membership library based on SWIM and gossip protocol.
Zuul - Gateway service that provides dynamic routing, monitoring, resiliency, security, and more.
Distributed Transactions
Distributed transactions provide a mechanism for ensuring consistency of data updates in the presence of concurrent access and partial failures.
Atomikos - Provides transactions for REST, SOA and microservices with support for JTA and XA.
Bitronix - Simple but complete implementation of the JTA 1.1 API.
Narayana - Provides support for traditional ACID and compensation transactions, also complies with JTA, JTS and other standards. (LGPL-2.1-only)
Seata - Delivers high performance and easy to use distributed transaction services under a microservices architecture.
Distribution
Tools that handle the distribution of applications in native formats.
Artipie - Binary artifact management toolkit which hosts them on the file system or S3.
Boxfuse - Deployment of JVM applications to AWS using the principles of immutable infrastructure.
Capsule - Simple and powerful packaging and deployment. A fat JAR on steroids, or a "Docker for Java" that supports JVM-optimized containers.
Central Repository - Largest binary component repository available as a free service to the open-source community. Default used by Apache Maven, and available in all other build tools.
Cloudsmith - Fully managed package management SaaS with support for Maven/Gradle/SBT with a free tier.
Getdown - A system for deploying Java applications to end-user computers and keeping them up to date. Developed as an alternative to Java Web Start.
IzPack - Setup authoring tool for cross-platform deployments.
JavaPackager - Maven and Gradle plugin which provides an easy way to package Java applications in native Windows, Mac OS X or GNU/Linux executables, and generate installers for them.
jDeploy - Deploy desktop apps as native Mac, Windows or Linux bundles.
jlink.online - Builds optimized runtimes over HTTP.
Nexus - Binary management with proxy and caching capabilities.
packr - Packs JARs, assets and the JVM for native distribution on Windows, Linux and macOS.
Formal-methods tools: proof assistants, model checking, symbolic execution, etc.
CATG - Concolic unit testing engine. Automatically generates unit tests using formal methods.
Checker Framework - Pluggable type systems. Includes nullness types, physical units, immutability types and more. (GPL-2.0-only WITH Classpath-exception-2.0)
Daikon - Detects likely program invariants and generates JML specs based on those invariants.
Java Path Finder (JPF) - JVM formal verification tool containing a model checker and more. Created by NASA.
JMLOK 2.0 - Detects inconsistencies between code and JML specification through feedback-directed random tests generation, and suggests a likely cause for each nonconformance detected. (GPL-3.0-only)
KeY - Formal software development tool that aims to integrate design, implementation, formal specification, and formal verification of object-oriented software as seamlessly as possible. Uses JML for specification and symbolic execution for verification. (GPL-2.0-or-later)
OpenJML - Translates JML specifications into SMT-LIB format and passes the proof problems implied by the program to backend solvers. (GPL-2.0-only)
Functional Programming
Libraries that facilitate functional programming.
Cyclops - Monad and stream utilities, comprehensions, pattern matching, functional extensions for all JDK collections, future streams, trampolines and much more.
derive4j - Java 8 annotation processor and framework for deriving algebraic data types constructors, pattern-matching and morphisms. (GPL-3.0-only)