Slice 3.0 introduces a simple validation mechanism which allows you to check if a model meets certain requirements or, in other words, is valid. Thanks to validation tag, a component whose model is not valid may not be displayed on a page.
Basic interfaces
The validation mechanism is based on two interfaces:
Validatable
If a class should be a subject to validation it should implement com.cognifide.slice.validation.api.Validatable. The interface introduces only one method: validate, which takes one argument: com.cognifide.slice.validation.api.ValidationResultBuilder. The argument allows you to define a validation messages of different levels. The levels include:
- error
- warning
- information
If at least one message has been added, the object is considered invalid. If there is no message, the object is considered valid.
An example usage of the interface is shown in the following listing. If the text property, mapped from the resource, is blank, the model is invalid.
import org.apache.commons.lang.StringUtils;
import com.cognifide.slice.mapper.annotation.JcrProperty;
import com.cognifide.slice.mapper.annotation.SliceResource;
import com.cognifide.slice.validation.api.Validatable;
import com.cognifide.slice.validation.api.ValidationResultBuilder;
@SliceResource
public class TextModel implements Validatable {
@JcrProperty
private String text;
@Override
public void validate(ValidationResultBuilder result) {
if (StringUtils.isBlank(text)) {
result.addErrorMessage("Text cannot be empty");
}
}
public String getText() {
return text;
}
}
Validator
The actual validation of an object is performed by com.cognifide.slice.validation.api.Validator interface. It defines one method: validate, which takes Validatable object as an argument. It returns ValidationResult as a result of validation. ValidationResult can be used for reading a result of validation and validation messages.
Slice's validation module provides a default implementation of the interface which can be used (injected) in your models to perform validation of objects of different types. Take a look at the example below where the model created by ModelProvider is validated before use.
import com.cognifide.slice.api.model.InitializableModel;
import com.cognifide.slice.api.provider.ModelProvider;
import com.cognifide.slice.mapper.annotation.JcrProperty;
import com.cognifide.slice.mapper.annotation.SliceResource;
import com.cognifide.slice.validation.api.Validator;
import com.cognifide.app.components.configuration.image.ImageConfigurationModel;
import com.google.inject.Inject;
@SliceResource
public class ImageModel implements InitializableModel {
@JcrProperty
private String configPath;
private int size;
private final ModelProvider modelProvider;
private final Validator validator;
@Inject
public ImageModel(final ModelProvider modelProvider, final Validator validator) {
this.modelProvider = modelProvider;
this.validator = validator;
}
@Override
public void afterCreated() {
ImageConfigurationModel configurationModel = modelProvider.get(ImageConfigurationModel.class, configPath);
if (validator.validate(configurationModel).isValid()) {
size = configurationModel.getDefaultSize();
} else {
...
}
}
...
}
Validation tag
To render a validation message to an end-user (author), you need to use a dedicated JSP tag - validate tag defined in the http://cognifide.com/jsp/slice/validation taglib. The example below shows an simple usage of it.
<%@page pageEncoding="UTF-8" contentType="text/html; charset=UTF-8"
%><%@include file="/apps/myapp/core/global.jsp"
%><slice:lookup var="model" type="<%=com.cognifide.myapp.components.richtext.TextModel.class%>"/>
<sv:validate object="${model}">
${model.text}
</sv:validate>
The taglib is registered under sv prefix. The TextModel object (obtained using <slice:lookup> tag) is validated in line 4. If the object is valid, the body of the validation tag will be rendered. Otherwise, error message will be output in the following format:
<div class="validationMessages">
<div class="title">
title <!-- only if defined -->
</div>
<ul class="errorMessages"> <!-- if error-level messages available -->
<li>Text cannot be empty</li>
<!-- stack trace --> <!-- if stack trace for the message is available, it is printed in HTML comment -->
</ul>
<ul class="warningMessages"> <!-- if warning-level messages available -->
<li>Some warning</li>
<!-- stack trace --> <!-- if stack trace for the message is available, it is printed in HTML comment -->
</ul>
<ul class="informationMessages"> <!-- if information-level messages available -->
<li>Some information</li>
<!-- stack trace --> <!-- if stack trace for the message is available, it is printed in HTML comment -->
</ul>
</div>
<div style="clear:both;font-size:1px"> </div>
Such format allows you to style them appropriately.