Jeroen’s Blog

In this article i will show you how to create custom labels for Java Enum types with a custom JSF converter. Click here to download the  example application. To run the example application you need Maven2. Simple type mvn jetty:run to start the embedded Jetty container. After a few seconds you can point your browser to http://localhost:8080/enumsample to see the application up and running.

To convert an enum type to a more friendly label, i’ve created a custom enum type converter. As you can see in the code below, that converter translate an enum value to a label in the message bundle. Based on the locale of your browser a localized messege will be returned.

package nl.jwse.sample.enumsample.converter;

import java.util.Locale;
import java.util.ResourceBundle;

import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.convert.Converter;

/**
 * Generic Enum Type converter. Converts an enum value to a language specific and display-friendly
 * label. The label should be defined in a messagebundle with the following convention.
 *
 * [Full enum classname].[Enum field]=Enter displaylabel here.
 *
 * i.e.
 *
 * nl.jwse.sample.enumsample.type.Card.HEARTS=Harten
 *
 * @author Jeroen Wolsink
 *
 */
public class EnumTypeConverter implements Converter {

	@SuppressWarnings("unchecked")
	public Object getAsObject(FacesContext fc, UIComponent comp,
			String value) {
		Class enumType = comp.getValueExpression("value").getType(fc.getELContext());
		return Enum.valueOf(enumType, value);
	}

	public String getAsString(FacesContext fc, UIComponent component,
			Object object) {
		if (object == null) {
			return null;
		}
		Enum type = (Enum) object;

		return getEnumLabel(type, fc);
	}

	/**
	 * Creates a localized label for the enum type. The label must be
	 * defined in the resource bundle, or else the toString() value will
	 * bee returned.
	 * @param type EnumType
	 * @param fc FacesContext
	 * @return The label for the enumerated type
	 */
	private String getEnumLabel(Enum type, FacesContext fc) {

		String label = null;

		String messageBundle = fc.getApplication().getMessageBundle();
		Locale locale = fc.getApplication().getDefaultLocale();
		ResourceBundle rb = ResourceBundle.getBundle(messageBundle, locale);
		try {
			String key = generateKey(type);
			label = rb.getString(key);
		} catch (Exception e) {
			label = type.toString();
		}

		return label;
	}

	/**
	 * Generates a message bundle key based on an Enum Type.
	 * @param type EnumType
	 * @return Message bundle key
	 */
	private String generateKey(Enum type) {

		String className = type.getClass().getName();
		String key = className + '.' + type.toString();

		return key;
	}
}

Before you can use the converter in your JSF page, the converter must be registered in the FacesContext.xml.

	enumTypeConverter
	nl.jwse.sample.enumsample.converter.EnumTypeConverter

In the page you can add the converter to an outputText usering the converter=”enumTypeConverter” attribute. In the backingbean there is also a conversion for the Card enum type to a selectItem list. You can view the implementation in the sourcefiles of the example application

I hope this article was helpfull to you. Any comments are most welcome.