com.opensymphony.xwork2.validator

## Interface Validator<T>

- All Known Subinterfaces:
    FieldValidator
  All Known Implementing Classes:
    ConditionalVisitorFieldValidator, ConversionErrorFieldValidator, CreditCardValidator, DateRangeFieldValidator, DoubleRangeFieldValidator, EmailValidator, ExpressionValidator, FieldExpressionValidator, FieldValidatorSupport, Form.FieldVisitorValidatorWrapper, IntRangeFieldValidator, LongRangeFieldValidator, RangeValidatorSupport, RegexFieldValidator, RepopulateConversionErrorFieldValidatorSupport, RequiredFieldValidator, RequiredStringValidator, ShortRangeFieldValidator, StringLengthFieldValidator, URLValidator, ValidatorSupport, VisitorFieldValidator

      public interface Validator<T>

  The validators supplied by the XWork distribution (and any validators you might write yourself) come in two different flavors:

  1. Plain Validators / Non-Field validators
  2. FieldValidators

  Plain Validators (such as the ExpressionValidator) perform validation checks that are not inherently tied to a single specified field. When you declare a plain Validator in your -validation.xml file you do not associate a fieldname attribute with it. (You should avoid using plain Validators within the <field-validator> syntax described below.)

  FieldValidators (such as the EmailValidator) are designed to perform validation checks on a single field. They require that you specify a fieldname attribute in your -validation.xml file. There are two different (but equivalent) XML syntaxes you can use to declare FieldValidators (see "<validator> vs. <field-Validator> syntax" below).

  There are two places where the differences between the two validator flavors are important to keep in mind:

  1. when choosing the xml syntax used for declaring a validator (either <validator> or <field-validator>)
  2. when using the short-circuit capability

  NOTE:Note that you do not declare what "flavor" of validator you are using in your -validation.xml file, you just declare the name of the validator to use and Struts will know whether it's a "plain Validator" or a "FieldValidator" by looking at the validation class that the validator's programmer chose to implement.

  To define validation rules for an Action, create a file named ActionName-validation.xml in the same package as the Action. You may also create alias-specific validation rules which add to the default validation rules defined in ActionName-validation.xml by creating another file in the same directory named ActionName-aliasName-validation.xml. In both cases, ActionName is the name of the Action class, and aliasName is the name of the Action alias defined in the xwork.xml configuration for the Action.

  The framework will also search up the inheritance tree of the Action to find validation rules for directly implemented interfaces and parent classes of the Action. This is particularly powerful when combined with ModelDriven Actions and the VisitorFieldValidator. Here's an example of how validation rules are discovered. Given the following class structure:

  - interface Animal;
  - interface Quadraped extends Animal;
  - class AnimalImpl implements Animal;
  - class QuadrapedImpl extends AnimalImpl implements Quadraped;
  - class Dog extends QuadrapedImpl;

  The framework method will look for the following config files if Dog is to be validated:

  - Animal
  - Animal-aliasname
  - AnimalImpl
  - AnimalImpl-aliasname
  - Quadraped
  - Quadraped-aliasname
  - QuadrapedImpl
  - QuadrapedImpl-aliasname
  - Dog
  - Dog-aliasname

  While this process is similar to what the XW:Localization framework does when finding messages, there are some subtle differences. The most important difference is that validation rules are discovered from the parent downwards.

  NOTE:Child's *-validation.xml will add on to parent's *-validation.xml according to the class hierarchy defined above. With this feature, one could have more generic validation rule at the parent and more specific validation rule at the child.

  There are two ways you can define validators in your -validation.xml file:

  1. <validator>
  2. <field-validator>

  Keep the following in mind when using either syntax:

  Non-Field-Validator The <validator> element allows you to declare both types of validators (either a plain Validator a field-specific FieldValidator).

          <!-- Declaring a plain Validator using the <validator> syntax: -->

          <validator type="expression>
                <param name="expression">foo gt bar</param>
                <message>foo must be great than bar.</message>
          </validator>

          <!-- Declaring a field validator using the <validator> syntax; -->

          <validator type="required">
               <param name="fieldName">bar</param>
               <message>You must enter a value for bar.</message>
          </validator>

  field-validator The <field-validator> elements are basically the same as the <validator> elements except that they inherit the fieldName attribute from the enclosing <field> element. FieldValidators defined within a <field-validator> element will have their fieldName automatically filled with the value of the parent <field> element's fieldName attribute. The reason for this structure is to conveniently group the validators for a particular field under one element, otherwise the fieldName attribute would have to be repeated, over and over, for each individual <validator>.

  HINT: It is always better to defined field-validator inside a <field> tag instead of using a <validator> tag and supplying fieldName as its param as the xml code itself is clearer (grouping of field is clearer)

  NOTE: Note that you should only use FieldValidators (not plain Validators) within a <field-validator> block. A plain Validator inside a <field> will not be allowed and would generate error when parsing the xml, as it is not allowed in the defined dtd (xwork-validator-1.0.2.dtd)

       Declaring a FieldValidator using the <field-validator> syntax:

       <field name="email_address">
         <field-validator type="required">
             <message>You cannot leave the email address field empty.</message>
         </field-validator>
         <field-validator type="email">
             <message>The email address you entered is not valid.</message>
         </field-validator>
       </field>

  The choice is yours. It's perfectly legal to only use <validator> elements without the <field> elements and set the fieldName attribute for each of them. The following are effectively equal:

       <field name="email_address">
         <field-validator type="required">
             <message>You cannot leave the email address field empty.</message>
         </field-validator>
         <field-validator type="email">
             <message>The email address you entered is not valid.</message>
         </field-validator>
       </field>

       <validator type="required">
         <param name="fieldName">email_address</param>
         <message>You cannot leave the email address field empty.</message>
       </validator>
       <validator type="email">
         <param name="fieldName">email_address</param>
         <message>The email address you entered is not valid.</message>
       </validator>

  It is possible to short-circuit a stack of validators. Here is another sample config file containing validation rules from the Xwork test cases: Notice that some of the <field-validator> and <validator> elements have the short-circuit attribute set to true.

       <!-- START SNIPPET: exShortCircuitingValidators -->
       <!DOCTYPE validators PUBLIC
               "-//Apache Struts//XWork Validator 1.0.3//EN"
                 "http://struts.apache.org/dtds/xwork-validator-1.0.3.dtd">
       <validators>
         <!-- Field Validators for email field -->
         <field name="email">
             <field-validator type="required" short-circuit="true">
                 <message>You must enter a value for email.</message>
             </field-validator>
             <field-validator type="email" short-circuit="true">
                 <message>Not a valid e-mail.</message>
             </field-validator>
         </field>
         <!-- Field Validators for email2 field -->
         <field name="email2">
            <field-validator type="required">
                 <message>You must enter a value for email2.</message>
             </field-validator>
            <field-validator type="email">
                 <message>Not a valid e-mail2.</message>
             </field-validator>
         </field>
         <!-- Plain Validator 1 -->
         <validator type="expression">
             <param name="expression">email.equals(email2)</param>
             <message>Email not the same as email2</message>
         </validator>
         <!-- Plain Validator 2 -->
         <validator type="expression" short-circuit="true">
             <param name="expression">email.startsWith('mark')</param>
             <message>Email does not start with mark</message>
         </validator>
       </validators>
       <!-- END SNIPPET: exShortCircuitingValidators -->

  short-circuiting and Validator flavors

  Plain validator takes precedence over field-validator. They get validated first in the order they are defined and then the field-validator in the order they are defined. Failure of a particular validator marked as short-circuit will prevent the evaluation of subsequent validators and an error (action error or field error depending on the type of validator) will be added to the ValidationContext of the object being validated.

  In the example above, the actual execution of validator would be as follows:

  1. Plain Validator 1
  2. Plain Validator 2
  3. Field Validators for email field
  4. Field Validators for email2 field

  Since Plain Validator 2 is short-circuited, if its validation failed, it will causes Field validators for email field and Field validators for email2 field to not be validated as well.

  Usefull Information: More complicated validation should probably be done in the validate() method on the action itself (assuming the action implements Validatable interface which ActionSupport already does).

  A plain Validator (non FieldValidator) that gets short-circuited will completely break out of the validation stack. No other validators will be evaluated and plain validators takes precedence over field validators meaning that they get evaluated in the order they are defined before field validators get a chance to be evaluated.

  Short cuircuiting and validator flavours

  A FieldValidator that gets short-circuited will only prevent other FieldValidators for the same field from being evaluated. Note that this "same field" behavior applies regardless of whether the <validator> or <field-validator> syntax was used to declare the validation rule. By way of example, given this -validation.xml file:

       <validator type="required" short-circuit="true">
         <param name="fieldName">bar</param>
         <message>You must enter a value for bar.</message>
       </validator>

       <validator type="expression">
         <param name="expression">foo gt bar</param>
         <message>foo must be great than bar.</message>
       </validator>

  both validators will be run, even if the "required" validator short-circuits. "required" validators are FieldValidator's and will not short-circuit the plain ExpressionValidator because FieldValidators only short-circuit other checks on that same field. Since the plain Validator is not field specific, it is not short-circuited.

  As mentioned above, the framework will also search up the inheritance tree of the action to find default validations for interfaces and parent classes of the Action. If you are using the short-circuit attribute and relying on default validators higher up in the inheritance tree, make sure you don't accidentally short-circuit things higher in the tree that you really want!

  The effect of having common validators on both

  - <actionClass>-validation.xml
  - <actionClass>-<actionAlias>-validation.xml

  It should be noted that the nett effect will be validation on both the validators available in both validation configuration file. For example if we have 'requiredstring' validators defined in both validation xml file for field named 'address', we will see 2 validation error indicating that the the address cannot be empty (assuming validation failed). This is due to WebWork will merge validators found in both validation configuration files.

  The logic behind this design decision is such that we could have common validators in <actionClass>-validation.xml and more context specific validators to be located in <actionClass>-<actionAlias>-validation.xml

  Validator's validation messages could be internatinalized. For example,

         <field-validator type="required">
            <message key="required.field" />
         </field-validator>

  or

         <validator type="expression">
            <param name="expression">email.startsWith('Mark')</param>
            <message key="email.invalid" />
         </validator>

  In the first case, WebWork would look for i18n with key 'required.field' as the validation error message if validation fails, and 'email.invalid' in the second case. We could also provide a default message such that if validation failed and the i18n key for the message cannot be found, WebWork would fall back and use the default message. An example would be as follows :-

         <field-validator type="required">
            <message key="required.field">This field is required.</message>
         </field-validator>

  or

         <validator type="expression">
            <param name="expression">email.startsWith('Mark')</param>
            <message key="email.invalid">Email needs with starts with Mark</message>
         </validator>

  Author:
    Jason Carreira

- - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `String` | `getDefaultMessage()` Gets the default message used for validation failures
    `String` | `getMessage(Object object)` Gets the validation failure message for the given object
    `String` | `getMessageKey()` Gets the resource bundle key used for lookup of validation failure message
    `String[]` | `getMessageParameters()` Gets the message parameters to be used when parsing i18n messages
    `ValidatorContext` | `getValidatorContext()` Gets the validation context used
    `String` | `getValidatorType()` Gets the validator type used (see class javadoc).
    `void` | `setDefaultMessage(String message)` Sets the default message to use for validation failure
    `void` | `setMessageKey(String key)` Sets a resource bundle key to be used for lookup of validation failure message
    `void` | `setMessageParameters(String[] messageParameters)` Sets the message parameters to be used when parsing i18n messages
    `void` | `setValidatorContext(ValidatorContext validatorContext)` This method will be called before validate with a non-null ValidatorContext.
    `void` | `setValidatorType(String type)` Sets the validator type to use (see class javadoc).
    `void` | `setValueStack(ValueStack stack)` Sets the value stack to use to resolve values and parameters
    `void` | `validate(Object object)` The validation implementation must guarantee that setValidatorContext will be called with a non-null ValidatorContext before validate is called.

- - ### Method Detail

    - #### setDefaultMessage

          void setDefaultMessage(String message)

      Sets the default message to use for validation failure
      Parameters:
        `message` - the default message

    - #### getDefaultMessage

          String getDefaultMessage()

      Gets the default message used for validation failures
      Returns:
        the default message

    - #### getMessage

          String getMessage(Object object)

      Gets the validation failure message for the given object
      Parameters:
        `object` - object being validated (eg. a domain model object)
      Returns:
        the validation failure message

    - #### setMessageKey

          void setMessageKey(String key)

      Sets a resource bundle key to be used for lookup of validation failure message
      Parameters:
        `key` - the resource bundle key

    - #### getMessageKey

          String getMessageKey()

      Gets the resource bundle key used for lookup of validation failure message
      Returns:
        the resource bundle key

    - #### setMessageParameters

          void setMessageParameters(String[] messageParameters)

      Sets the message parameters to be used when parsing i18n messages
      Parameters:
        `messageParameters` - the message parameters

    - #### getMessageParameters

          String[] getMessageParameters()

      Gets the message parameters to be used when parsing i18n messages
      Returns:
        the message parameters

    - #### setValidatorContext

          void setValidatorContext(ValidatorContext validatorContext)

      This method will be called before validate with a non-null ValidatorContext.
      Parameters:
        `validatorContext` - the validation context to use.

    - #### getValidatorContext

          ValidatorContext getValidatorContext()

      Gets the validation context used
      Returns:
        the validation context

    - #### validate

          void validate(Object object)
                        throws ValidationException

      The validation implementation must guarantee that setValidatorContext will be called with a non-null ValidatorContext before validate is called.
      Parameters:
        `object` - the object to be validated.
      Throws:
        `ValidationException` - is thrown if there is validation error(s).

    - #### setValidatorType

          void setValidatorType(String type)

      Sets the validator type to use (see class javadoc).
      Parameters:
        `type` - the type to use.

    - #### getValidatorType

          String getValidatorType()

      Gets the validator type used (see class javadoc).
      Returns:
        the type used

    - #### setValueStack

          void setValueStack(ValueStack stack)

      Sets the value stack to use to resolve values and parameters
      Parameters:
        `stack` - The value stack for the request
      Since:
        2.1.1

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