Apache Hadoop - Storage and large-scale processing of data-sets on clusters of commodity hardware.
Apache OpenNLP - Toolkit for common tasks like tokenization.
Apache Velocity - Templates for HTML pages, emails or source code generation in general.
FreeMarker - General templating engine without any heavyweight or opinionated dependencies.
GlassFish - Application server and reference implementation for Java EE sponsored by Oracle.
GWT - Toolbox which includes a Java-to-JavaScript compiler for client-side code, XML parser, API for RPC, JUnit integration, internationalization support and widgets for the GUI.
HornetQ - Clear, concise, modular and made to be embedded.
Hudson - Continuous integration server still in active development.
Java Modeling Language (JML) - Behavioral interface specification language that can be used to specify the behavior of code modules. It combines the design by contract approach of Eiffel and the model-based specification approach of the Larch family of interface specification languages, with some elements of the refinement calculus. Used by several other verification tools.
JavaCC - More specific and slightly easier to learn. Has syntactic lookahead.
JavaServer Faces - Oracle's open-source implementation of the JSF standard, Mojarra.
JavaServer Pages - Common templating for websites with custom tag libraries.
Dozer - Mapper that copies data from one object to another, using annotations, API or XML configuration.
JMapper - Using byte code manipulation for lightning fast mapping. Supporting annotations, API or XML configuration.
MapStruct - Code generator which simplifies mappings between different bean types, based on a convention over configuration approach.
ModelMapper - ModelMapper is an intelligent object mapping library that automatically maps objects to each other.
Orika - Orika is a Java Bean mapping framework that recursively copies (among other capabilities) data from one object to another.
Selma - Stupid Simple Statically Linked Mapper. Selma is an Annotation Processor Based bean mapper.
Build
Tools which handle the build cycle and dependencies of an application.
Apache Maven - Declarative build and dependency management which favors convention over configuration. It might be preferable to Apache Ant which uses a rather procedural approach and can be difficult to maintain.
Bazel - Build tool from Google that builds code quickly and reliably.
Gradle - Incremental builds which are 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.
Byteman - Manipulate bytecode at runtime via DSL (rules) mainly for testing/troubleshooting.
Frameworks which can dynamically manage applications inside of a cluster.
Apache Aurora - Apache Aurora is a Mesos framework for long-running services and cron jobs.
Apache Mesos - Abstracts CPU, memory, storage, and other compute resources away from machines.
Singularity - Singularity is a 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.
Codacy - Continuous static analysis, code coverage, and software metrics to automate code reviews.
Error Prone - Catches common programming mistakes as compile-time errors.
FindBugs - Static analysis of bytecode to find potential bugs.
jQAssistant - Static code analysis with Neo4J-based query language.
PMD - Source code analysis for finding bad coding practices.
SonarQube - Integrates other analysis components via plugins and provides an overview of the metrics over time.
Spoon - Library for analyzing and transforming Java source code.
Code Coverage
Frameworks and tools that enable collection of code coverage metrics for test suites.
Clover - Proprietary code coverage tool by Atlassian that 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; GPLv2 licensed.
JaCoCo - Framework that enables collection of code coverage metrics, using both offline and runtime bytecode instrumentation; prominently used by EclEmma, the Eclipse code-coverage plugin.
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.
FreeBuilder - Automatic generation of the Builder pattern.
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.
Lombok - Code generator which aims to reduce verbosity.
Command-line Argument Parsers
Libraries that make it easy to parse command line options, arguments, etc.
Airline - Annotation-based framework for parsing Git like command line arguments.
args4j - Small library to parse command like arguments similar to javac.
JCommander - Command line arguments parsing framework with custom types and validation via implementing interfaces.
JOpt Simple - Simple parser that uses the POSIX getopt() and GNU getopt_long() syntaxes. Does not use annotations, uses a fluent API instead.
Compiler-compiler
Frameworks that help to create parsers, interpreters or compilers.
ANTLR - Complex full-featured framework for top-down parsing.
DCEVM - Modification of the JVM that allows unlimited redefinition of loaded classes at runtime.
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.
JavaParser - Parse, modify and generate Java code.
Druid - Real-time and historical OLAP data store that excel at aggregation and approximation queries.
Infinispan - Highly concurrent key/value datastore used for caching.
OpenTSDB - Scalable and distributed time series database written on top of Apache HBase.
OrientDB - Embeddable distributed database written on top of Hazelcast.
Distribution
Tools which handle the distribution of applications in native formats.
Bintray - Version control for binaries which handles the publishing. Can also be used with Maven or Gradle and has a free plan for open-source software or several business plans.
Boxfuse - Deployment of JVM application 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.
IzPack - Setup authoring tool for cross-platform deployments.
JitPack - Easy to use package repository for GitHub. Builds Maven/Gradle projects on demand and publishes ready-to-use packages.
Nexus - Binary management with proxy and caching capabilities.
packr - Packs JARs, assets and the JVM for native distribution on Windows, Linux and Mac OS X.
Libraries that assist with processing office document formats.
Apache POI - Supports OOXML (XLSX, DOCX, PPTX) as well as OLE2 (XLS, DOC or PPT).
documents4j - API for document format conversion using third-party converters such as MS Word.
docx4j - Creating and manipulating Microsoft Open XML files.
Formal Verification
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.
Daikon - Daikon detects likely program invariants and can generate JML specs based on those invariats.
Java Path Finder (JPF) - JVM formal verification tool containing a model checker and more. Created by NASA.
JMLOK 2.0 - Detects nonconformances between code and JML specification through the feedback-directed random tests generation, and suggests a likely cause for each nonconformance detected.
KeY - The KeY System is a 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.
OpenJML - Translates JML specifications into SMT-LIB format and passes the proof problems implied by the program to backend solvers.
Functional Programming
Libraries that facilitate functional programming.
cyclops-react - 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, morphisms.
Integrated development environments that try to simplify several aspects of development.
Eclipse - Established, open-souce project with support for lots of plugins and languages.
IntelliJ IDEA - Supports a lot of JVM languages and provides good options for Android development. The commercial edition targets the enterprise sector.
NetBeans - Provides integration for several Java SE and EE features from database access to HTML5.
Imagery
Libraries that assist with the creation, evaluation or manipulation of graphical images.
Imgscalr - Simple and efficient hardware-accelerated image-scaling library implemented in pure Java 2D.
SLF4J - Abstraction layer which is to be used with an implementation.
tinylog - Lightweight logging framework with static logger class.
Tracer - Call tracing and log correlation in distributed systems.
Machine Learning
Tools that provide specific statistical algorithms which allow learning from data.
Apache Flink - Fast and reliable large-scale data processing engine.
Apache Mahout - Scalable algorithms focused on collaborative filtering, clustering and classification.
Apache Spark - Data analytics cluster computing framework.
DatumBox - Provides several algorithms and pre-trained models for natural language processing.
DeepDive - Creates structured information from unstructured data and integrates it into an existing database.
Deeplearning4j - Distributed and multi-threaded deep learning library.
H2O - Analytics engine for statistics over big data.
JSAT - Algorithms for pre-processing, classification, regression, and clustering with support for multi-threaded execution.
Oryx 2 - A framework for building real-time large scale machine learning applications, which also includes end-to-end applications for collaborative filtering, classification, regression, and clustering.
Smile - The Statistical Machine Intelligence and Learning Engine provides a set of machine learning algorithms and a visualization library.
Weka - Collection of algorithms for data mining tasks ranging from pre-processing to visualization.
Messaging
Tools that help to send messages between clients in order to ensure protocol independency.
Aeron - Efficient reliable unicast and multicast message transport.
Apache ActiveMQ - Message broker that implements JMS and converts synchronous to asynchronous communication.
Apache Camel - Glues together different transport APIs via Enterprise Integration Patterns.
JavaMelody - Performance monitoring and profiling.
jmxtrans - Tool to connect to multiple JVMs and to query them for their attributes via JMX. Its query language is based on JSON, which allows non-Java programmers to access the JVMs attributes. Likewise, this tool supports different output writes, including Graphite, Ganglia, StatsD, among others.
Prometheus - Provides a multi-dimensional data model, DSL, autonomous server nodes and much more.
SPM - Performance monitor with distributing transaction tracing for JVM apps.
Stagemonitor - Open source performance monitoring and transaction tracing for JVM apps.
Native
For working with platform-specific native libraries.
JNA - Work with native libraries without writing JNI. Also provides interfaces to common system libraries.
JNR - Work with native libraries without writing JNI. Also provides interfaces to common system libraries. Same goals as JNA, but faster, and serves as the basis for the upcoming Project Panama.
Natural Language Processing
Libraries that specialize on processing text.
CoreNLP - Stanford's CoreNLP provides a set of fundamental tools for tasks like tagging, named entity recognition, sentiment analysis and many more.
DKPro - A collection of re-usable NLP tools for linguistic pre-processing, machine learning, lexical resources, etc.
LingPipe - Toolkit for a variety of tasks ranging from POS tagging to sentiment analysis.
Comsat - Integrates standard Java web-related APIs with Quasar fibers and actors.
Finagle - Extensible RPC system used to construct high-concurrency servers. It implements uniform client and server APIs for several protocols, and is protocol agnostic, which simplifies the implementation of new protocols.
Grizzly - NIO framework. Used as a network layer in Glassfish.
gRPC - RPC framework based on protobuf and HTTP/2.
MINA - Abstract event-driven async I/O API for network operations over TCP/IP and UDP/IP via Java NIO.
Netty - Framework for building high performance network applications.
Nifty - Implementation of Thrift clients and servers on Netty.
Riptide - Client-side response routing for Spring's RestTemplate.
Undertow - Web server providing both blocking and non-blocking API’s based on NIO. Used as a network layer in WildFly.
urnlib - Java library for representing, parsing and encoding URNs as in RFC 2141.
ORM
APIs which handle the persistence of objects.
Apache Cayenne - Provides clean, static API for data access. Also includes GUI Modeler for working with database mappings, DB reverse engineering and generation.
JITWatch - Analyze the JIT compiler optimisations made by the HotSpot JVM.
JMH - JMH is a Java harness for building, running, and analysing nano/micro/milli/macro benchmarks written in Java and other languages targeting the JVM.
Microserver — A convenient extensible Microservices plugin system for Spring & Spring Boot, with over 30 plugins and growing, that supports both micro-monolith and pure microservices styles.
RAML - Modeling language to generate REST APIs with contract first.
Rapidoid - A simple, secure and extremely fast framework consisting of embedded HTTP server, GUI components and dependency injection.
rest.li - Framework for building robust, scalable RESTful architectures using type-safe bindings and asynchronous, non-blocking IO with an end-to-end developer workflow that promotes clean practices, uniform interface design and consistent data modeling.
RESTEasy - Fully certified and portable implementation of the JAX-RS specification.
RestExpress - Thin wrapper on the JBoss Netty HTTP stack to provide scaling and performance.
Restlet Framework - Pioneering framework with powerful routing and filtering capabilities, unified client and server API.
Swagger - Swagger is a specification and complete framework implementation for describing, producing, consuming, and visualizing RESTful web services.
Science
Libraries for scientific computing, analysis and visualization.
DataMelt - Environment for scientific computation, data analysis and data visualization.
GraphStream - Library for modeling and analysis of dynamic graphs.
JGraphT - Graph library that provides mathematical graph-theory objects and algorithms.
JGraphX - Library for visualisation (mainly Swing) and interaction with node-edge graphs.
Search
Engines which index documents for search and analysis.
Apache Lucene - High-performance, full-featured cross-platform text search engine library.
Apache Solr - Enterprise search engine optimized for high volume traffic.
Elasticsearch - Distributed, multitenant-capable full-text search engine with a RESTful web interface and schema-free JSON documents.
Security
Libraries that handle security, authentication, authorization or session management.
Apache Shiro - Performs authentication, authorization, cryptography and session management.
Bouncy Castle - All-purpose cryptographic library. JCA provider, wide range of functions from basic helpers to PGP/SMIME operations.
Cryptomator - Multiplatform transparent client-side encryption of files in the cloud.
Hdiv - Runtime application self-protection against OWASP Top 10 security risks such us Insecure Direct Object References, SQL injection, Cross-Site Scripting (XSS), Cross-Site Request Forgery (CSRF) and much more.
jjwt - Java JWT: JSON Web Token for Java and Android.
Keycloak - Integrated SSO and IDM for browser apps and RESTful web services.
Keyczar - Easy to use, yet safe encryption framework with key versioning.
JSoup - Scrapes, parses, manipulates and cleans HTML.
Web Frameworks
Frameworks that handle the communication between the layers of an web application.
Apache Tapestry - Component-oriented framework for creating dynamic, robust, highly scalable web applications.
Apache Wicket - Component-based web application framework similar to Tapestry with a stateful GUI.
Baratine - Toolkit for building distributed and reactive applications for multiple environments, either standalone or embedded.
Blade - Lightweight, modular framework which aims to be elegant and simple.
Bootique - Minimally opinionated framework for runnable apps.
Grails - Groovy framework with the aim to provide a highly productive environment by favoring convention over configuration, no XML and support for mixins.
Jooby - Scalable, fast and modular micro framework which offers multiple programming models.
Websites that provide a frontend for this list. Please note, there won't be an official website. We don't associate with a particular website and everybody is allowed to create one.
