Creating a custom validator

Explains how to write and integrate custom validators for Tapestry 4 and 5

Tapestry 5.0

Author: Sebastian Hennebrueder, Date: August 2009 There are 3 steps:

  1. Create a validator
  2. Create a resource file for validation messages
  3. Register both in your application

Create a validator

The following validator check if the value is not 'foo' because foo is really a bad value. It expects a String and no configuration parameter. The MinLength validator uses a configuration parameter to define the minimum length. The validation error messages has the key foo-not-allowed. You might check the source code of the existing validators for further inspiration.

import org.apache.tapestry5.validator.AbstractValidator;
// ... some more imports here
public class FooValidator extends AbstractValidator<Void, String> {
	public FooValidator() {
		super(null, String.class, "foo-not-allowed");
	}

	public void validate(Field field, Void constraintValue, MessageFormatter formatter, String value)
			throws ValidationException {
		if ("foo". equals(value))
			throw new ValidationException(buildMessage(formatter, field, constraintValue));
	}

	private String buildMessage(MessageFormatter formatter, Field field, Void constraintValue) {
		return formatter.format(constraintValue, field.getLabel());
	}

	public void render(Field field, Void constraintValue, MessageFormatter formatter, MarkupWriter writer,
										 FormSupport formSupport) {
		formSupport.addValidation(field, "foo", buildMessage(formatter, field, constraintValue), null);
	}
}

Create a resource file for validation messages

File ValidationMessages.properties

foo-not-allowed=Foo is not allowed

Register both in your application

A Tapestry application is configured by a AppModule class (See the Tapestry Guide). In the AppModule class add the following methods:

  public static void contributeValidationMessagesSource(OrderedConfiguration<String> configuration) {
    configuration.add("Default", "de/laliluna/example/components/ValidationMessages", "before:*");
  }

  public static void contributeFieldValidatorSource(MappedConfiguration<String, Validator> configuration) {
    configuration.add("foo", new FooValidator());
  }

That's it.

Tapestry 4.0

this is a revised copy of a posing to the users mailing list by Scott F. Walter

1. implementing a validator

Create a class that extends org.apache.tapestry.form.validator.BaseValidator
(note, this is not org.apache.tapestry.valid.BaseValidator )

Override the validate method.

If you want a parameter to be passed into your validator:

  1. create a constructor that takes a String
  2. add a (non abstract) property (setXXX, getXXX) where XXX will be the name of your validator. E.g. if the validator is called

mustBe, use getMustBe(), setMustBe(String). Later on you will reference the validator using: mustBe=tapestry

Here is an example:

package dummy;

import org.apache.tapestry.form.IFormComponent;
import org.apache.tapestry.form.ValidationMessages;
import org.apache.tapestry.form.validator.BaseValidator;
import org.apache.tapestry.valid.ValidatorException;

/**
 * @author scott/ron
 */
public class MustBeValidator extends BaseValidator {
 
   private String _mustBe;
   
   public MustBeValidator() {
     super();
   }
   
   public MustBeValidator(String string) {
     super(string);
   }

   public void setMustBe(String s) {
     _mustBe = s;
   }

   public String getMustBe() {
     return _mustBe;
   }

   public void validate(IFormComponent field,
             ValidationMessages messages,
             java.lang.Object object)
             throws ValidatorException {
             if (!equal(object,_mustBe) {
           throw new ValidatorException(messages.formatValidationMessage(getMessage(), "invalid-format", null));
       }                
   }

   private boolean equal(Object o1, Object o2) {
     if (o1 == null && o2 == null)
       return true;
     if (o1 == null || o2 == null)
       return false;
     return o1.equals(o2);
   }
}

configuration

Provide a contribution to tapestry.form.validator.Validators in hivemodule.xml (stored in your WEB-INF directory)

{{{<?xml version="1.0"?>
<module id="myApplicationName" version="1.0.0">
<contribution configuration-id="tapestry.form.validator.Validators">
<validator name="mustBe" configurable="true" class="dummy.MustBeValidator"/>
</contribution>
</module>
}}}

Note: If your validator does not take any parameters set configurable to "false" here

Using

Inside the specification file, use the new validator as follows:

 <component id="firstNameField" type="TextField">
   <binding name="value" value="ognl:person.firstName"/>
   <binding name="validators" value="required,minLength=3,mustBe=Scott"/>
   <binding name="displayName" value="First Name"/>
 </component>
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