Open Source Validation Frameworks

Reusable validation methods and configurable (typically XML) validation engine for client and server-side data; common rules for email, dates, URLs; usable with Struts.

Extensible validation framework for any Java object; constraints via annotations, XML, POJOs, or scripting (Groovy, BeanShell, JavaScript); optional AspectJ for design-by-contract.

Validation framework with rules in declarative Java (not XML/annotations); objects validate themselves; callback interfaces for failure handling; extensible DSL.

Library for processing and validating HTML forms; automates input validation by criteria, type conversion, and bean population; no XML required.

Extensible JavaBean validation library; constraints via annotations, XDoclet, or programmatic; i18n; integration with JSF and Wicket.

Java object validation framework for JavaBeans and other objects; validity defined via configuration.

Spring add-ons including validation: commons-validator integration and Valang-based declarative constraints on domain models (XML, Java 5 annotations); built on Spring Validator.