Validating User Input - Stripes...and Java Web Development is Fun Again - page 59

Return to source page,
display error messages

Browser

request

validation
errors

Action Bean

parameter
binding

Validation

no validation
errors

Execute event handler

Figure 4.1: The validation sequence

We now have a clearly defined validation for the age property. Submit-
ting the form with the Age field left blank, or filled in with a value less
than eighteen, produces a validation error. As illustrated in Figure 4.1 ,
Stripes does not execute the intended event handler when a validation
error occurs. Instead, the user is sent back to the form that was sub-
mitted. This way, we can safely save data in the event handler method
because we know that Stripes won't call it if the data is invalid. All
we need to do is to add the <s:errors> tag to our JSP to display error
messages, and we're done!

Nested Properties
@Validate works only in an action bean. Annotating properties of a plain
model class won't work, because Stripes doesn't go searching for anno-
tations in model classes. Does this mean you have to copy properties
from a model class to an action bean? Of course not—that wouldn't be
very Stripesy! Just like forms, validations support nested properties. 1

Remember that a nested property is a property of a property, such as 1. getPer-

son().getAge() .