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Apache Struts 2 Documentation
FieldExpressionValidator Annotation
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This validator uses an OGNL expression to perform its validator. The error message will be added to the field if the expression returns false when it is evaluated against the value stack.

## Usage

The annotation must be applied at method level.

## Parameters

Parameter | Required | Default | Notes
--- | --- | --- | ---
message | yes |  | field error message
key | no |  | i18n key from language specific properties file.
messageParams | no |  | Additional params to be used to customize message - will be evaluated against the Value Stack
fieldName | no |  |
shortCircuit | no | false | If this validator should be used as shortCircuit.
expression | yes |  | An OGNL expression that returns a boolean value.

## Examples