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This is an excellent question. Let's step back a second and think about a typical mid to large size application. If we start from the back end and work toward the view we have:
1) Database: Most modern databases are going to validate for required fields, duplicate records, security constraints, etc.
2) Business Logic: Here you are going to check for valid data relationships and things that make sense for the particular problem you are triing to solve.
... This is where struts comes into the picture, by now the system should be pretty well bulletproof. What we are going to do is make validation friendlier and informative. Rember it is OK to have duplicate validations...
ActionErrors validate(ActionMapping map, HttpServletRequest req)
is where you can do your validation and feed back to the view, information
required to correct any errors.
validate is run after the form
reset and after the
have been set from corresponding view based input. Also remember you can turn
validation off with
validate="false" in the
mapping in the
struts-config.xml. This is done by returning an
collection with messages from your
Here you have access to the request so you can see what kinds of action is
being requested to fine tune your validations. The <html:error> tag
allows you to dump all errors on your page or a particular error associated
with a particular property. The
input attribute of the
action allows you to send validation errors to a particular jsp /
html / tile page.
4) You can have the system perform low level validations and client side
feedback using a
ValidatorForm or its derivatives. This will
entry errors. You code your validations in the
file. A working knowledge of regular expressions is necessary to use this
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