Struts 2 validation is configured via XML or annotations. Manual validation in the action is also possible, and may be combined with XML- and annotation-driven validation.
Validation also depends on both the "validation" and "workflow" interceptors (both are included in the default interceptor stack). The "validation" interceptor does the validation itself and creates a list of field-specific errors. The "workflow" interceptor checks for the presence of validation errors: if any are found, it returns the "input" result (by default), taking the user back to the form which contained the validation errors.
If we're using the default settings and our action doesn't have an "input" result defined and there are validation (or, incidentally, type conversion) errors, we'll get an error message back telling us there's no "input" result defined for the action.
CONTENTS
Using Annotations
Annotations can be used as an alternative to XML for validation.
Examples
In all examples given here, the validation message displayed is given in plain English - to internationalize the message, put the string in a properties file and use a property key instead, specified by the 'key' attribute. It will be looked up by the framework (see Localization).
- Basic Validation
- Client-side Validation
- AJAX Validation
- Using Field Validators
- Using Non Field Validators
- Using Visitor Field Validator
- How do we repopulate controls when validation fails (FAQ entry)
Bundled Validators
Note
When using a Field Validator, Field Validator Syntax is ALWAYS preferable than using the Plain Validator Syntax as it facilitates grouping of field-validators according to fields. This is very handy especially if a field needs to have many field-validators which is almost always the case.
- conversion validator
- date validator
- double validator
- email validator
- expression validator
- fieldexpression validator
- int validator
- regex validator
- required validator
- requiredstring validator
- stringlength validator
- url validator
- visitor validator
Registering Validators
The following list shows the default validators included in the framework and is an example of the syntax used to declare our own validators.
Struts 2.0.7 and Prior
The validators.xml containing custom validators needs to contain a copy of the default validators. No DTD was used in validators.xml. See: http://struts.apache.org/2.x/docs/release-notes-208.html#ReleaseNotes2.0.8-MigrationfrompreviousReleases
Turning on Validation
The default interceptor stack, "defaultStack", already has validation turned on. When creating your own interceptor-stack be sure to include both the "validation" and "workflow" interceptors. From struts-default.xml:
<interceptor-stack name="defaultStack">
...
<interceptor-ref name="validation">
<param name="excludeMethods">input,back,cancel,browse</param>
</interceptor-ref>
<interceptor-ref name="workflow">
<param name="excludeMethods">input,back,cancel,browse</param>
</interceptor-ref>
</interceptor-stack>
Beginning with version 2.0.4 Struts provides an extension to XWork's com.opensymphony.xwork2.validator.ValidationInterceptor interceptor.
<interceptor name="validation" class="org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor"/>
This interceptor allows us to turn off validation for a specific method by using the @org.apache.struts2.interceptor.validation.SkipValidation annotation on the action method.
Validator Scopes
Notes
Defining Validation Rules
In this context, "Action Alias" refers to the action name as given in the Struts configuration. Often, the name attribute matches the method name, but they may also differ.