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## Chapter 11. JSF form validation in Seam

In plain JSF, validation is defined in the view:

    <h:form>

        <h:messages/>

        <div>

            Country:

            <h:inputText value="#{location.country}" required="true">

                <my:validateCountry/>

            </h:inputText>

        </div>

        <div>

            Zip code:

            <h:inputText value="#{location.zip}" required="true">

                <my:validateZip/>

            </h:inputText>

        </div>

        <h:commandButton/>

    </h:form>

In practice, this approach usually violates DRY, since most "validation" actually enforces constraints that are part of the data model, and exist all the way down to the database schema definition. Seam provides support for model-based constraints defined using Bean Validation.

Let's start by defining our constraints, on our `Location` class:

    public class Location {

        private String country;

        private String zip;

        @NotNull

        @Size(max=30)

        public String getCountry() { return country; }

        public void setCountry(String c) { country = c; }

        @NotNull

        @Size(max=6)

        @Pattern("^\d*$")

        public String getZip() { return zip; }

        public void setZip(String z) { zip = z; }

    }

Well, that's a decent first cut, but in practice it might be more elegant to use custom constraints instead of the ones built into Bean Validation:

    public class Location {

        private String country;

        private String zip;

        @NotNull

        @Country

        public String getCountry() { return country; }

        public void setCountry(String c) { country = c; }

        @NotNull

        @ZipCode

        public String getZip() { return zip; }

        public void setZip(String z) { zip = z; }

    }

Whichever route we take, we no longer need to specify the type of validation to be used in the JSF page. Instead, we can use `<s:validate>` to validate against the constraint defined on the model object.

    <h:form>

        <h:messages/>

        <div>

            Country:

            <h:inputText value="#{location.country}" required="true">

                <s:validate/>

            </h:inputText>

        </div>

        <div>

            Zip code:

            <h:inputText value="#{location.zip}" required="true">

                <s:validate/>

            </h:inputText>

        </div>

        <h:commandButton/>

    </h:form>

Note: specifying `@NotNull` on the model does not eliminate the requirement for `required="true"` to appear on the control! This is due to a limitation of the JSF validation architecture.

This approach defines constraints on the model, and presents constraint violations in the view — a significantly better design.

However, it is not much less verbose than what we started with, so let's try `<s:validateAll>`:

    <h:form>

        <h:messages/>

        <s:validateAll>

            <div>

                Country:

                <h:inputText value="#{location.country}" required="true"/>

            </div>

            <div>

                Zip code:

                <h:inputText value="#{location.zip}" required="true"/>

            </div>

            <h:commandButton/>

        </s:validateAll>

    </h:form>

This tag simply adds an `<s:validate>` to every input in the form. For a large form, it can save a lot of typing!

Now we need to do something about displaying feedback to the user when validation fails. Currently we are displaying all messages at the top of the form. In order for the user to correlate the message with an input, you need to define a label using the standard `label` attribute on the input component.

    <h:inputText value="#{location.zip}" required="true" label="Zip:">

        <s:validate/>

    </h:inputText>

You can then inject this value into the message string using the placeholder {0} (the first and only parameter passed to a JSF message for a Bean Validation restriction). See the internationalization section for more information regarding where to define these messages.

    validator.length={0} length must be between {min} and {max}

What we would really like to do, though, is display the message next to the field with the error (this is possible in plain JSF), highlight the field and label (this is not possible) and, for good measure, display some image next to the field (also not possible). We also want to display a little colored asterisk next to the label for each required form field. Using this approach, the identifying label is not necessary.

That's quite a lot of functionality we need for each field of our form. We wouldn't want to have to specify highlighting and the layout of the image, message and input field for every field on the form. So, instead, we'll specify the common layout in a facelets template:

    <ui:composition xmlns="http://www.w3.org/1999/xhtml"

                    xmlns:ui="http://java.sun.com/jsf/facelets"

                    xmlns:h="http://java.sun.com/jsf/html"

                    xmlns:f="http://java.sun.com/jsf/core"

                    xmlns:s="http://jboss.org/schema/seam/taglib">

        <div>

            <s:label styleClass="#{invalid?'error':''}">

                <ui:insert name="label"/>

                <s:span styleClass="required" rendered="#{required}">*</s:span>

            </s:label>

            <span class="#{invalid?'error':''}">

                <h:graphicImage value="/img/error.gif" rendered="#{invalid}"/>

                <s:validateAll>

                    <ui:insert/>

                </s:validateAll>

            </span>

            <s:message styleClass="error"/>

        </div>

    </ui:composition>

We can include this template for each of our form fields using `<s:decorate>`.

    <h:form>

        <h:messages globalOnly="true"/>

        <s:decorate template="edit.xhtml">

            <ui:define name="label">Country:</ui:define>

            <h:inputText value="#{location.country}" required="true"/>

        </s:decorate>

        <s:decorate template="edit.xhtml">

            <ui:define name="label">Zip code:</ui:define>

            <h:inputText value="#{location.zip}" required="true"/>

        </s:decorate>

        <h:commandButton/>

    </h:form>

Finally, we can use RichFaces Ajax to display validation messages as the user is navigating around the form:

    <h:form>

        <h:messages globalOnly="true"/>

        <s:decorate id="countryDecoration" template="edit.xhtml">

            <ui:define name="label">Country:</ui:define>

            <h:inputText value="#{location.country}" required="true">

                <a:ajax event="blur" render="countryDecoration" bypassUpdates="true"/>

            </h:inputText>

        </s:decorate>

        <s:decorate id="zipDecoration" template="edit.xhtml">

            <ui:define name="label">Zip code:</ui:define>

            <h:inputText value="#{location.zip}" required="true">

                <a:ajax event="blur" render="zipDecoration" bypassUpdates="true"/>

            </h:inputText>

        </s:decorate>

        <h:commandButton/>

    </h:form>

It's better style to define explicit ids for important controls on the page, especially if you want to do automated testing for the UI, using some toolkit like Selenium. If you don't provide explicit ids, JSF will generate them, but the generated values will change if you change anything on the page.

    <h:form id="form">

        <h:messages globalOnly="true"/>

        <s:decorate id="countryDecoration" template="edit.xhtml">

            <ui:define name="label">Country:</ui:define>

            <h:inputText id="country" value="#{location.country}" required="true">

                <a:ajax event="blur" render="countryDecoration" bypassUpdates="true"/>

            </h:inputText>

        </s:decorate>

        <s:decorate id="zipDecoration" template="edit.xhtml">

            <ui:define name="label">Zip code:</ui:define>

            <h:inputText id="zip" value="#{location.zip}" required="true">

                <a:ajax event="blur" render="zipDecoration" bypassUpdates="true"/>

            </h:inputText>

        </s:decorate>

        <h:commandButton/>

    </h:form>

And what if you want to specify a different message to be displayed when validation fails? You can use the Seam message bundle (and all it's goodies like el expressions inside the message, and per-view message bundles) with the Bean Validation:

    public class Location {

        private String name;

        private String zip;

        // Getters and setters for name

        @NotNull

        @Size(max=6)

        @ZipCode(message="#{messages['location.zipCode.invalid']}")

        public String getZip() { return zip; }

        public void setZip(String z) { zip = z; }

    }

    location.zipCode.invalid = The zip code is not valid for #{location.name}

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