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Some knowledge of wicket property-resource loading is required to understand this article.

As of wicket-1.1 post rc2 there is an easier way to provide validation messages for form components.

In wicket-1.1-rc2 and before the validation messages were provided through resource keys defined as form-id.form-component-id.validator-class-name. This approach entailed a lot of repetitive resource messages. For example, the following form:

Form form=new Form("myform");
form.add(new RequiredTextField("firstname").add(LengthValidator.max(15));
form.add(new RequiredTextField("lastname").add(LengthValidator.max(15));

would have required the following resource keys:

[page-class-name].properties
----------------------------
myform.firstname.RequiredValidator=Field 'customer first name' is required
myform.firstname.LengthValidator=Field 'customer first name' must be between ${min} and ${max} characters
myform.lastname.RequiredValidator=Field 'customer last name' is required
myform.lastname.LengthValidator=Field 'customer last name' must be between ${min} and ${max} characters

Wicket-1.1 post rc2 provides a much simplified approach by introducing the ${label} variable in the validation context which represents the user-centric name of the form component and allows factoring out validator-specific messages into one place.

The ${label} variable can be provided by one of two ways:
It can either be set directly on the form component instance by calling setLabel(IModel model) method, or by including a resource key of the form form-id.form-component-id.

The example above can now be rewritten as following:

Specify the general validator messages:

[webapplication-subclass-name].properties
RequiredValidator=Field '${label}' is required
LengthValidator=Field '${label}' must be between ${min} and ${max} characters

Specify the user-centric form component labels:

[page-class-name].properties
myform.firstname=customer first name
myform.lastname=customer last name

or specify labels directly in java code:

FormComponent firstname=new RequiredTextField("firstname").add(LengthValidator.max(15));
firstname.setLabel(new Model("customer first name"));
form.add(firstname);
FormComponent lastname=new RequiredTextField("lastname").add(LengthValidator.max(15));
lastname.setLabel(new Model("customer last name"));
form.add(lastname);

This approach makes it much simpler to maintain error messages in forms.

Since 1.2 (CVS HEAD) the following features have been added:
Let's say you have the following component hierarchy:

APage
->BForm id="b"
{panel}
 -->XPanel id="x"
    ---->RequiredTextField id="foo"
 -->YPanel id="y"
    ---->RequiredTextField id="foo"
{panel}

XPanel knows nothing about its containing form or page, nevertheless XPanel's validation keys was required to be prefixed with the form's id

{panel}
 XPanel.properties:
   b.foo.RequiredValidator = Foo is required.
{panel}

That introduced an unwanted dependency of XPanel on its parental form (i.e. id="b").

Furthermore there was no way to override the foo messages separately for XPanel and YPanel:

{panel}
 APage.properties:
   b.foo.RequiredValidator = Foo is required in x ??
   b.foo.RequiredValidator = Foo is required in y ??
{panel}

That has been changed. The search order has been changed like that:

{panel}
 APage.properties:
   b.x.foo.RequiredValidator = Foo is extremely required.
 XPanel.properties:
   foo.RequiredValidator = Foo is required.
{panel}

YPanel's validation text could stay unaltered:

{panel}
 YPanel.properties:
   foo.RequiredValidator = Foo is required.
{panel}
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