Document that @Validated results in the use of a proxy and warn users about the side-effects

[wilkinsona]

Affects: All supported versions

Using @Validated can result in a CGLib proxy being created for a bean. This has the sometimes unexpected side-effect of changing how the bean's fields behave when accessed directly. Please see this Spring Boot issue for an example of a problem that this unexpected behavior can cause.

I think it would be good if the Framework reference documentation noted the use of a proxy and forewarned users about the side-effects.

[rstoyanchev]

We can add something to this section.

Looking through that entire 3.7 Spring Validation it looks like it could use a little bit of polishing, e.g. to avoid dated references to features added in Spring Framework 3. Also the title of that section should really be Bean Validation API as it is focused on JSR-303 support specifically (the section id is already bean-validation).

This in contrast to and in addition to coverage of "Spring Validation" earlier at the top of Section 3 which covers the Spring Validator contract in more detail. Those parts could use a little polishing as well.