An ActionForm is a JavaBean optionally associated with one or more ActionMappings. Such a bean will have had its properties initialized from the corresponding request parameters before the corresponding Action.execute method is called.

When the properties of this bean have been populated, but before the execute method of the Action is called, this bean's validate method will be called, which gives the bean a chance to verify that the properties submitted by the user are correct and valid. If this method finds problems, it returns an error messages object that encapsulates those problems, and the controller servlet will return control to the corresponding input form. Otherwise, the validate method returns null, indicating that everything is acceptable and the corresponding Action.execute method should be called.

This class must be subclassed in order to be instantiated. Subclasses should provide property getter and setter methods for all of the bean properties they wish to expose, plus override any of the public or protected methods for which they wish to provide modified functionality.

Because ActionForms are JavaBeans, subclasses should also implement Serializable, as required by the JavaBean specification. Some containers require that an object meet all JavaBean requirements in order to use the introspection API upon which ActionForms rely.