A Spring Converter bridges two types during data binding. It implements Converter and its convert() method, turning submitted values such as ingredient IDs into richer domain objects. section 2.2
Converting ingredient IDs
A checkbox submission may contain ["FLTO", "GRBF", "LETC"], while Taco expects a List<Ingredient>. IngredientByIdConverter implements Converter<String, Ingredient>, stores ingredients in a Map, and uses each submitted ID to return the matching Ingredient. Annotating the class with @Component makes it discoverable; Spring Boot automatically registers Converter beans with Spring MVC for request-parameter binding. The example uses hardcoded ingredients and defers database-backed lookup. section 2.2
