OutputLabel.java

/*
 * Copyright 2017 OmniFaces
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */
package org.omnifaces.component.output;

import static java.lang.String.format;
import static org.omnifaces.util.Components.findComponentRelatively;
import static org.omnifaces.util.Components.getOptionalLabel;
import static org.omnifaces.util.Components.setLabel;
import static org.omnifaces.util.Utils.isEmpty;

import javax.el.ValueExpression;
import javax.faces.component.FacesComponent;
import javax.faces.component.UIComponent;
import javax.faces.component.html.HtmlOutputLabel;
import javax.faces.event.ComponentSystemEvent;
import javax.faces.event.PostRestoreStateEvent;

/**
 * <p>
 * The <code><o:outputLabel></code> is a component that extends the standard <code><h:outputLabel></code>
 * with support for automatically setting its value as the label of the component identified by its <code>for</code>
 * attribute (if any). This way there's no need to duplicate the very same label into the <code>label</code> attribute
 * of the input component. After submitting the form without having entered a value, a validation message is posted that
 * should contain the label printed before the input instead of some generated ID.
 * <p>
 * You can use it the same way as <code><h:outputLabel></code>, you only need to change <code>h:</code> into
 * <code>o:</code>.
 *
 * @author Arjan Tijms
 */
@FacesComponent(OutputLabel.COMPONENT_TYPE)
public class OutputLabel extends HtmlOutputLabel {

	public static final String COMPONENT_TYPE = "org.omnifaces.component.output.OutputLabel";

	private static final String ERROR_FOR_COMPONENT_NOT_FOUND =
		"A component with Id '%s' as specified by the for attribute of the OutputLabel with Id '%s' could not be found.";

	@Override
	public void processEvent(ComponentSystemEvent event) {
		if (event instanceof PostRestoreStateEvent) {
			String forValue = (String) getAttributes().get("for");
			if (!isEmpty(forValue)) {
				UIComponent forComponent = findComponentRelatively(this, forValue);

				if (forComponent == null) {
					throw new IllegalArgumentException(format(ERROR_FOR_COMPONENT_NOT_FOUND, forValue, getId()));
				}

				// To be sure, check if the target component doesn't have a label already. This
				// is unlikely, since otherwise people have no need to use this outputLabel component
				// but check to be sure.
				if (getOptionalLabel(forComponent) == null) {
					ValueExpression valueExpression = getValueExpression("value");
					setLabel(forComponent, valueExpression != null ? valueExpression : getValue());
				}
			}
		}

	}
}