Recipe8.10.Adding a Custom Validation to a Validator Form

Recipe 8.10. Adding a Custom Validation to a Validator Form

Problem

You need to add a custom ad hoc validation check to a Validator ActionForm.

Solution

Extend the ValidatorForm or ValidatorActionForm and override the validate( ) method, ensuring you call super.validate( ) to perform the Validator's validation. (See Example 8-14.)

Example 8-14. Extending the ValidatorForm

import javax.servlet.http.HttpServletRequest; import org.apache.struts.action.ActionError; import org.apache.struts.action.ActionErrors; import org.apache.struts.action.ActionMapping; import org.apache.struts.validator.ValidatorForm; public final class MyForm extends ValidatorForm {     private String foo;     private String bar;     public String getFoo( ) {         return foo;     }     public void setFoo(String s) {         foo = s;     }     public String getBar( ) {         return bar;     }     public void setBar(String s) {         bar = s;     }     public ActionErrors validate(ActionMapping mapping,                                   HttpServletRequest request) {         // Perform validator framework validations         ActionErrors errors = super.validate(mapping, request);                // Add crossfield and business validations here         if (!checkFooBarValid(foo, bar)) {             errors.add("foo", new ActionError("errors.invalidFooBar"));         }         // additional validations ...         return errors;     }     private boolean checkFooBarValid(Foo foo, Bar bar) {         boolean valid = false;         // perform custom validation         valid = FooBarUtil.checkFooBar(foo, bar);         return valid;     } }

If you're using a dynamic form defined in the struts-config.xml, extend the type being used (e.g., DynaValidatorForm), and override the validate( ) method as the class does in Example 8-15.

Example 8-15. Extending the DynaValidatorForm

package com.mycompany.myapp; import javax.servlet.http.HttpServletRequest; import org.apache.struts.action.ActionError; import org.apache.struts.action.ActionErrors; import org.apache.struts.action.ActionMapping; import org.apache.struts.validator.DynaValidatorForm; public final class MyDynaForm extends DynaValidatorForm {     public ActionErrors validate(ActionMapping mapping,                                   HttpServletRequest request) {         // Perform validator framework validations         ActionErrors errors = super.validate(mapping, request);         // get the needed property values         String foo = (String) get("foo");         String bar = (String) get("bar");                // Add crossfield and business validations here         if (!checkFooBarValid(foo, bar)) {           errors.add("foo", new ActionError("errors.invalidFooBar"));         }         // additional validations ...         return errors;     }     private boolean checkFooBarValid(Foo foo, Bar bar) {         boolean valid = false;         // perform custom validation         valid = FooBarUtil.checkFooBar(foo, bar);         return valid;     } }

Then change the form-bean element to use this new class:

<form-bean name="SomeForm"             type="com.mycompany.myapp.MyDynaForm">     <form-property name="foo" type="java.lang.String"/>     <form-property name="bar" type="java.lang.String"/> </form-bean>

Discussion

Though the Validator offloads much of your hand-written code to a configuration file, more complex validations may be required. Two general types of validation exist: syntactic and semantic. Syntactic validation verifies the syntax of the data, and semantic validation verifies that the data is meaningful from a business sense. The Validator does syntactic checks well but isn't purposed for semantic validation. Usually, this validation needs to be hand-written.

Fortunately, the Validator doesn't prohibit you from providing additional custom validations. For conventional hand-coded ActionForms that extend ValidatorForm or ValidatorActionForm, override the validate( ) method to add the additional validation checks. In your validate( ) method, call super.validate( ) to allow the Validator to perform its verifications. Then perform additional validations in your own method as required. If an error occurs, add it to the ActionErrors object returned from super.validate( ).

If you are using the Validator with dynamic action forms, then your form bean typically uses a type of DynaValidatorForm or DynaValidatorActionForm. Apply the same technique for extending these classes as with conventional nondynamic form classes. You extend the form class and override the validate method. To access properties of a DynaValidatorForm, you'll need to use the get(property) methods.

Recipe8.10.Adding a Custom Validation to a Validator Form