This model class encapsulates the full power of localization support within the Wicket framework. It combines the flexible Wicket resource loading mechanism with property expressions, property models and standard Java
MessageFormat substitutions. This combination should be able to solve any dynamic localization requirement that a project has.
The model should be created with four parameters, which are described in detail below:
- resourceKey - This is the most important parameter as it contains the key that should be used to obtain resources from any string resource loaders. This parameter is mandatory: a null value will throw an exception. Typically it will contain an ordinary string such as "label.username". To add extra power to the key functionality the key may also contain a property expression which will be evaluated if the model parameter (see below) is not null. This allows keys to be changed dynamically as the application is running. For example, the key could be "product.${product.id}" which prior to rendering will call model.getObject().getProduct().getId() and substitute this value into the resource key before is is passed to the loader.
- component - This parameter should be a component that the string resource is relative to. In a simple application this will usually be the Page on which the component resides. For reusable components/containers that are packaged with their own string resource bundles it should be the actual component/container rather than the page. For more information on this please see {@link org.apache.wicket.resource.loader.ComponentStringResourceLoader}. The relative component may actually be {@code null} if this model is wrapped on assignment ({@link IComponentAssignedModel}) or when all resource loading is to be done from a global resource loader. However, we recommend that a relative component is still supplied even in the latter case in order to 'future proof' your application with regards to changing resource loading strategies.
- model - This parameter is mandatory if either the resourceKey, the found string resource (see below) or any of the substitution parameters (see below) contain property expressions. Where property expressions are present they will all be evaluated relative to this model object. If there are no property expressions present then this model parameter may be
null - parameters - The parameters parameter allows an array of objects to be passed for substitution on the found string resource (see below) using a standard
java.text.MessageFormat object. Each parameter may be an ordinary Object, in which case it will be processed by the standard formatting rules associated with java.text.MessageFormat. Alternatively, the parameter may be an instance of IModel in which case the getObject() method will be applied prior to the parameter being passed to the java.text.MessageFormat. This allows such features dynamic parameters that are obtained using a PropertyModel object or even nested string resource models.
As well as the supplied parameters, the found string resource can contain formatting information. It may contain property expressions in which case these are evaluated using the model object supplied when the string resource model is created. The string resource may also contain
java.text.MessageFormat style markup for replacement of parameters. Where a string resource contains both types of formatting information then the property expression will be applied first.
Example 1
In its simplest form, the model can be used as follows:
public class MyPage extends WebPage<Void> { public MyPage(final PageParameters parameters) { add(new Label("username", new StringResourceModel("label.username", this, null))); } } Where the resource bundle for the page contains the entry
label.username=Username Example 2
In this example, the resource key is selected based on the evaluation of a property expression:
public class MyPage extends WebPage<Void> { public MyPage(final PageParameters parameters) { WeatherStation ws = new WeatherStation(); add(new Label("weatherMessage", new StringResourceModel("weather.${currentStatus}", this, new Model<WeatherStation>(ws))); } } Which will call the WeatherStation.getCurrentStatus() method each time the string resource model is used and where the resource bundle for the page contains the entries:
weather.sunny=Don't forget sunscreen! weather.raining=You might need an umbrella weather.snowing=Got your skis? weather.overcast=Best take a coat to be safe
Example 3
In this example the found resource string contains a property expression that is substituted via the model:
public class MyPage extends WebPage<Void> { public MyPage(final PageParameters parameters) { WeatherStation ws = new WeatherStation(); add(new Label("weatherMessage", new StringResourceModel("weather.message", this, new Model<WeatherStation>(ws))); } } Where the resource bundle contains the entry
weather.message=Weather station reports that the temperature is ${currentTemperature} ${units} Example 4
In this example, the use of substitution parameters is employed to format a quite complex message string. This is an example of the most complex and powerful use of the string resource model:
public class MyPage extends WebPage<Void> { public MyPage(final PageParameters parameters) { WeatherStation ws = new WeatherStation(); IModel<WeatherStation> model = new Model<WeatherStation>(ws); add(new Label("weatherMessage", new StringResourceModel( "weather.detail", this, model, new Object[] { new Date(), new PropertyModel<?>(model, "currentStatus"), new PropertyModel<?>(model, "currentTemperature"), new PropertyModel<?>(model, "units") })); } } And where the resource bundle entry is:
weather.detail=The report for {0,date}, shows the temperature as {2,number,###.##} {3} \ and the weather to be {1}
@see ComponentStringResourceLoader for additional information especially on the component searchorder
@author Chris Turner