[jira] [Created] (TAP5-2763) @RequestParameter improved blank handling

["Ben Weidig (Jira)" <ji...@apache.org>]

Ben Weidig created TAP5-2763:
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             Summary: @RequestParameter improved blank handling
                 Key: TAP5-2763
                 URL: https://issues.apache.org/jira/browse/TAP5-2763
             Project: Tapestry 5
          Issue Type: Improvement
          Components: tapestry-core
    Affects Versions: 5.8.3
            Reporter: Ben Weidig


As ValueEncoders are used to convert a parameter value to its actual type, only Boolean and Number-based types result directly in {{null}} for a blank value.
All other types use their TypeCoercer-based ValueEncoder, which not necessarily work.
However, I believe that if {{allowBlank = true}} is set, then a blank parameter should be able to lead to a {{null}} value.

Three possible changes come to mind to support blank --> null:
 * Always treat blank as {{null}} before passing it the ValueEncoder
 * Add {{boolean treatBlankAsNull() default false;}} to {{@RequestParameter, or}}
 * {{adding String blankValue() String default ""; to @RequestParameter that is used instead of the parameter value if blank}}

Personally, I'd prefer the first option.
The {{TypeCoercedValueEncoderFactory}} would handle {{{}Boolean{}}}/{{{}Number{}}} just like before, but @RequestParamter wouldn't crash anymore if no valid coercion is possible for an empty String.

My proof-of-concept works and I might provide a feature branch soon.



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