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The sample page

Code Block

	xml
	xml
title	The sample pagexml

<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
<html>
<head>
  <title>Hello World!</title>
</head>
<body>
<f:view>
  <h:form id="mainForm">
    <h:panelGrid columns="3">
      <h:outputLabel for="name" value="Please enter your name" />
      <h:inputText id="name" value="#{helloWorld.name}" />
      <h:message for="name" showSummary="true" showDetail="false" />

      <h:commandButton value="Press me" action="#{helloWorld.send}" />
      <h:panelGroup />
      <h:panelGroup />
    </h:panelGrid>
  </h:form>
</f:view>
</body>
</html>

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The sample bean

Code Block

	java
	java
title	Fragment of the HelloWorldController beanjava

public class HelloWorldController {
    
    @Required
    private String name;

    // getters and setters omitted for brevity
}

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Cross validation

Code Block

	java
	java
title	Usage of cross validationjava

public class Person {

    @NotEquals("lastName")
    private String firstName;

    private String lastName;

    // Getters and setters omitted for brevity
}

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Note

title	Hint

If you don't like the default conventions, you can provide a custom name mapper, or you provide a mapping between annotations and the validation strategies (via properties file or ExtVal Java API), or ...

Code Block

	java
	java
title	Minimal custom constraintjava

package my.custom.package

@Target({METHOD, FIELD})
@Retention(RUNTIME)
public @interface CustomConstraint {
}

Note that this is just a minimalistic annotation definition. There's nothing ExtVal-specific here.

Code Block

	java
	java
title	Minimal validation strategy implementationjava

package my.custom.package

public class CustomConstraintValidationStrategy implements ValidationStrategy {

    public void validate(FacesContext facesContext, UIComponent uiComponent,
                         MetaDataEntry metaDataEntry, Object convertedObject) {

        //custom validation logic
    }
}

...

The class below implements the validation strategy for the @Equals annotation. Note that the class can be relatively simple, since the hard work is done for us in the AbstractCompareStrategy.

Code Block

	java
	java
title	Custom cross-validation strategies	java

@SkipValidationSupport
public class EqualsStrategy extends AbstractCompareStrategy {

    public boolean useTargetComponentToDisplayErrorMsg(CrossValidationStorageEntry crossValidationStorageEntry) {
        return true;
    }

    protected String getValidationErrorMsgKey(Annotation annotation, boolean isTargetComponent) {
        return ((Equals) annotation).validationErrorMsgKey();
    }

    public boolean isViolation(Object object1, Object object2, Annotation annotation) {
        return object1 != null && !object1.equals(object2);
    }

    public String[] getValidationTargets(Annotation annotation) {
        return ((Equals) annotation).value();
    }
}

...

As we've seen before, we can easily reference a property within the same bean by using the property name.

Code Block

	java
	java
title	Referencing a local property	java

public class Person
{
    @NotEquals("lastName")
    private String firstName;

    private String lastName;
...
}

We can also refer to properties of related beans, as is shown in the example below:

Code Block

	java
	java
title	Referencing a property of a local referencejava

public class RegistrationPage
{
    private Person person = new Person();

    @Equals("person.password")
    private String oldPassword;
...
}

It is even possible to use EL-like expressions to refer to properties of beans that will be available at runtime.

Code Block

	java
	java
title	Referencing a property of a beanjava

public class RegistrationPage
{
    @Equals("#{person.password}")
    private String oldPassword;
...
}

...

Solution: The validation strategy optionally provides a meaningful validation error message. It's called a reverse validation error message.

Code Block

	java
	java
title	Example	java

...
    @Override
    protected String getReverseErrorMessageSummary(Annotation annotation)
    {
        return "meaningful validation error message summary";
    }
...
    @Override
    protected String getReverseErrorMessageDetail(Annotation annotation)
    {
        return "meaningful validation error message details";
    }
...

...

It's possible since the first version of ExtVal. Due to new features introduced in the 3rd release of ExtVal you will see additional things in the example you might not have seen so far. However, they aren't required since the approach just uses the mechanism of cross-validation.:

Code Block

	java
	java
title	Custom cross-validation annotation	java

@Target({METHOD, FIELD})
@Retention(RUNTIME)
@Documented
@UsageInformation(UsageCategory.API)
public @interface ValidateLengthIf
{
    String[] validateIf();

    int minimum() default 0;

    int maximum() default Integer.MAX_VALUE;

    Class<? extends ValidationParameter>[] parameters() default ViolationSeverity.Error.class;
}

Code Block

	java
	java
title	Custom cross-validation strategyjava

@SkipValidationSupport
public class ValidateLengthIfValidationStrategy extends AbstractCompareStrategy<ValidateLengthIf>
{
    private UIComponent component;
    private FacesMessage facesMessage;

    @Override
    protected void initCrossValidation(CrossValidationStorageEntry crossValidationStorageEntry)
    {
        this.component = crossValidationStorageEntry.getComponent();
    }

    public boolean isViolation(Object source, Object target, ValidateLengthIf annotation)
    {
        if (Boolean.TRUE.equals(target))
        {
            try
            {
                LengthValidator lengthValidator = resolveLengthValidator();
                lengthValidator.setMinimum(annotation.minimum());
                lengthValidator.setMaximum(annotation.maximum());
                lengthValidator.validate(FacesContext.getCurrentInstance(), this.component, source);
            }
            catch (ValidatorException e)
            {
                this.facesMessage = e.getFacesMessage();
                return true;
            }
        }
        return false;
    }

    private LengthValidator resolveLengthValidator()
    {
        return (LengthValidator)FacesContext.getCurrentInstance()
                .getApplication().createValidator("javax.faces.Length");
    }

    public String[] getValidationTargets(ValidateLengthIf annotation)
    {
        return annotation.validateIf();
    }

    @Override
    public boolean useTargetComponentToDisplayErrorMsg(CrossValidationStorageEntry crossValidationStorageEntry)
    {
        return false;
    }

    @Override
    protected String getErrorMessageSummary(ValidateLengthIf annotation, boolean isTargetComponent)
    {
        return this.facesMessage.getSummary();
    }

    @Override
    protected String getErrorMessageDetail(ValidateLengthIf annotation, boolean isTargetComponent)
    {
        return this.facesMessage.getDetail();
    }

    protected String getValidationErrorMsgKey(ValidateLengthIf annotation, boolean isTargetComponent)
    {
        //for using the message of the std. validator instead of a cross-validation-key for extval message resolving
        return null;
    }
}

...

Register a resource-bundle file which contains an annotation/validation strategy mapping:

Code Block

	java
	java
title	Alternative config approach via a property filejava

StaticConfiguration<String, String> staticConfig = new StaticResourceBundleConfiguration();
staticConfig.setSourceOfMapping("[custom package + name of the properties file.]");
ExtValContext.getContext().addStaticConfiguration(StaticConfigurationNames.META_DATA_TO_VALIDATION_STRATEGY_CONFIG, staticConfig);

...

This approach is more typesafe - a simple example:

Code Block

	java
	java
title	Alternative config approach which manual mappingjava

StaticInMemoryConfiguration staticConfig = new StaticInMemoryConfiguration();
staticConfig.addMapping(CustomConstraint.class.getName(), CustomValidator.class.getName());
ExtValContext.getContext().addStaticConfiguration(StaticConfigurationNames.META_DATA_TO_VALIDATION_STRATEGY_CONFIG, staticConfig);

...

Inject a Spring bean into the validation strategy
AOP exception handling
...

Code Block

	xml
	xml
title	Spring based dependency injection support for validation strategiesxml

<!-- The name of annotation: @CustomRequired -->

<!-- Part of the Spring configuration: -->

<bean id="customRequiredValidationStrategy" class="..." lazy-init="true">
    <property name="messageResolver" ref="customMsgResolver"/>
    <property name="requiredValidationService" ref="demoRequiredValidationService"/>
</bean>

<bean id="customMsgResolver" 
      class="org.apache.myfaces.extensions.validator.core.validation.message.resolver.DefaultValidationErrorMessageResolver"
      lazy-init="true">

    <!-- With JSF 1.2 you can use the var name of resource-bundle see faces-config.xml -->
    <property name="messageBundleVarName" value="messages"/>
</bean>

<bean id="demoRequiredValidationService" class="..."/>

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The sample page

The sample bean

Cross validation