Validation, Data Binding, and Type Conversion

There are pros and cons for considering validation as business logic, and Spring offers a design for validation and data binding that does not exclude either one of them. Specifically, validation should not be tied to the web tier and should be easy to localize, and it should be possible to plug in any available validator. Considering these concerns, Spring provides a Validator contract that is both basic and eminently usable in every layer of an application.spring-doc.cn

Data binding is useful for letting user input be dynamically bound to the domain model of an application (or whatever objects you use to process user input). Spring provides the aptly named DataBinder to do exactly that. The Validator and the DataBinder make up the validation package, which is primarily used in but not limited to the web layer.spring-doc.cn

The BeanWrapper is a fundamental concept in the Spring Framework and is used in a lot of places. However, you probably do not need to use the BeanWrapper directly. Because this is reference documentation, however, we feel that some explanation might be in order. We explain the BeanWrapper in this chapter, since, if you are going to use it at all, you are most likely do so when trying to bind data to objects.spring-doc.cn

Spring’s DataBinder and the lower-level BeanWrapper both use PropertyEditorSupport implementations to parse and format property values. The PropertyEditor and PropertyEditorSupport types are part of the JavaBeans specification and are also explained in this chapter. Spring’s core.convert package provides a general type conversion facility, as well as a higher-level format package for formatting UI field values. You can use these packages as simpler alternatives to PropertyEditorSupport implementations. They are also discussed in this chapter.spring-doc.cn

Spring supports Java Bean Validation through setup infrastructure and an adaptor to Spring’s own Validator contract. Applications can enable Bean Validation once globally, as described in Java Bean Validation, and use it exclusively for all validation needs. In the web layer, applications can further register controller-local Spring Validator instances per DataBinder, as described in Configuring a DataBinder, which can be useful for plugging in custom validation logic.spring-doc.cn