DO NOT REPLY [Bug 17104] New: - Newbie FAQ - When is the best time to validate input?

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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=17104

Newbie FAQ - When is the best time to validate input?

           Summary: Newbie FAQ - When is the best time to validate input?
           Product: Struts
           Version: Unknown
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Enhancement
          Priority: Other
         Component: Documentation
        AssignedTo: struts-dev@jakarta.apache.org
        ReportedBy: edgar@blue-moose.net


<p>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:</p>
<p>1) Database:  Most modern databases are going to validate for required 
fields, duplicate records, security constraints, etc.</p>
<p>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.</p>
<p>... 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...</p>
<p>3) <code>ActionErrors validate(ActionMapping map, HttpServletRequest req)
</code> is where you can do your validation and feed back to the view, 
information required to correct any errors.  <code>validate</code> is run after 
the form has been <code>reset</code> and after the <code>ActionForm</code> 
properties have been set from corresponding view based input. Also remember you 
can turn validation off with <code>validate="false"</code> in the 
<code>action</code> mapping in the <code>struts-config.xml</code>. This is done 
by returning an <code>ActionErrors</code> collection with messages from your 
<code>ApplicationResources.properties</code> file.</p>
<p>Here you have access to the request so you can see what kinds of action is 
being requested to fine tune your validations.  The &lt;html:error&gt; tag 
allows you to dump all errors on your page or a particular error associated 
with a particular property.  The <code>input</code> attribute of the 
<code>struts-config.xml</code> <code>action</code> allows you to send 
validation errors to a particular jsp / html / tile page.</p>
<p>4) You can have the system perform low level validations and client side 
feedback using a <code>ValidatorForm</code> or its derivatives.  This will 
generate javascript and give instant feedback to the user for simple data entry 
errors.  You code your validations in the <code>validator-rules.xml</code> 
file.  A working knowledge of <a 
href="http://etext.lib.virginia.edu/helpsheets/regex.html">regular 
expressions</a> is necessary to use this feature effectively.  For more 
information
<p><a 
href="http://jakarta.apache.org/struts/userGuide/dev_validator.html">http://jaka
rta.apache.org/struts/userGuide/dev_validator.html</a></p>

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