ViewParam.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.input;

import static org.omnifaces.util.Faces.getELContext;
import static org.omnifaces.util.Faces.isPostback;

import java.util.Map;

import javax.el.ValueExpression;
import javax.faces.component.FacesComponent;
import javax.faces.component.UIInput;
import javax.faces.component.UIViewParameter;
import javax.faces.context.FacesContext;
import javax.faces.event.PostValidateEvent;
import javax.faces.event.PreValidateEvent;

import org.omnifaces.util.MapWrapper;
import org.omnifaces.util.Utils;

/**
 * <p>
 * The <code><o:viewParam></code> is a component that extends the standard <code><f:viewParam></code> and
 * provides a stateless mode of operation and fixes the issue wherein null model values are converted to empty string
 * parameters in query string (e.g. when <code>includeViewParams=true</code>) and the (bean) validation never being
 * triggered when the parameter is completely absent in query string, causing e.g. <code>@NotNull</code> to fail.
 *
 * <h3>Stateless mode to avoid unnecessary conversion, validation and model updating on postbacks</h3>
 * <p>
 * The standard {@link UIViewParameter} implementation calls the model setter again after postback. This is not always
 * desired when being bound to a view scoped bean and can lead to performance problems when combined with an expensive
 * converter. To solve this, this component by default stores the submitted value as a component property instead of in
 * the model (and thus in the view state in case the binding is to a view scoped bean).
 * <p>
 * The standard {@link UIViewParameter} implementation calls the converter and validators again on postbacks. This is
 * not always desired when you have e.g. a <code>required="true"</code>, but the parameter is not retained on form
 * submit. You would need to retain it on every single command link/button by <code><f:param></code>. To solve
 * this, this component doesn't call the converter and validators again on postbacks.
 *
 * <h3>Using name as default for label</h3>
 * <p>
 * The <code><o:viewParam></code> also provides a default for the <code>label</code> atrribute. When the
 * <code>label</code> attribute is omitted, the <code>name</code> attribute will be used as label.
 *
 * <h3>Avoid unnecessary empty parameter in query string</h3>
 * <p>
 * The standard {@link UIViewParameter} implementation calls the converter regardless of whether the evaluated model
 * value is <code>null</code> or not. As converters by specification return an empty string in case of <code>null</code>
 * value, this is being added to the query string as an empty parameter when e.g. <code>includeViewParams=true</code> is
 * used. This is not desired. The workaround was added in OmniFaces 1.8.
 *
 * <h3>Support bean validation and triggering validate events on null value</h3>
 * <p>
 * The standard {@link UIViewParameter} implementation uses in JSF 2.0-2.2 an internal "is required" check when the
 * submitted value is <code>null</code>, hereby completely bypassing the standard {@link UIInput} validation, including
 * any bean validation annotations and even the {@link PreValidateEvent} and {@link PostValidateEvent} events. This is
 * not desired. The workaround was added in OmniFaces 2.0. In JSF 2.3, this has been fixed and has only effect when
 * <code>javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL</code> context param is set to <code>true</code>.
 *
 * <h3>Default value when no parameter is set</h3>
 * <p>
 * The <code><o:viewParam></code> also supports providing a default value via the new <code>default</code>
 * attribute. When the parameter is not available, then the value specified in <code>default</code> attribute will be
 * set in the model instead. The support was added in OmniFaces 2.2.
 *
 * <h3>Usage</h3>
 * <p>
 * You can use it the same way as <code><f:viewParam></code>, you only need to change <code>f:</code> to
 * <code>o:</code>.
 * <pre>
 * <o:viewParam name="foo" value="#{bean.foo}" />
 * </pre>
 *
 * @author Arjan Tijms
 * @author Bauke Scholtz
 */
@FacesComponent(ViewParam.COMPONENT_TYPE)
public class ViewParam extends UIViewParameter {

	// Public constants -----------------------------------------------------------------------------------------------

	public static final String COMPONENT_TYPE = "org.omnifaces.component.input.ViewParam";

	// Variables ------------------------------------------------------------------------------------------------------

	private String submittedValue;
	private Map<String, Object> attributeInterceptMap;

	// Actions --------------------------------------------------------------------------------------------------------

	@Override
	public void processDecodes(FacesContext context) {
		// Ignore any request parameters that are present when the postback is done.
		if (!context.isPostback()) {
			super.processDecodes(context);
		}
	}

	@Override
	public void processValidators(FacesContext context) {
		if (!context.isPostback()) {
			if (isEmpty(getSubmittedValue())) {
				setSubmittedValue(getDefault());
			}

			if (getSubmittedValue() == null) {
				setSubmittedValue(""); // Workaround for it never triggering the (bean) validation when unspecified.
			}

			super.processValidators(context);
		}
	}

	@Override
	public Map<String, Object> getAttributes() {
		if (attributeInterceptMap == null) {
			attributeInterceptMap = new AttributeInterceptMap(super.getAttributes());
		}

		return attributeInterceptMap;
	}

	/**
	 * When there's a value expression and the evaluated model value is <code>null</code>, then just return
	 * <code>null</code> instead of delegating to default implementation which would return an empty string when a
	 * converter is attached.
	 * @since 1.8
	 */
	@Override
	public String getStringValueFromModel(FacesContext context) {
		ValueExpression ve = getValueExpression("value");
		Object value = (ve != null) ? ve.getValue(context.getELContext()) : null;
		return (value != null) ? super.getStringValueFromModel(context) : null;
	}

	// Attribute getters/setters --------------------------------------------------------------------------------------

	@Override
	public String getSubmittedValue() {
		return submittedValue;
	}

	@Override
	public void setSubmittedValue(Object submittedValue) {
		this.submittedValue = (String) submittedValue; // Don't delegate to statehelper to keep it stateless.
	}

	/**
	 * Returns the default value in case the actual request parameter is <code>null</code> or empty.
	 * @return The default value in case the actual request parameter is <code>null</code> or empty.
	 * @since 2.2
	 */
	public String getDefault() {
		return (String) getStateHelper().eval("default");
	}

	/**
	 * Sets the default value in case the actual request parameter is <code>null</code> or empty.
	 * @param defaultValue The default value in case the actual request parameter is <code>null</code> or empty.
	 * @since 2.2
	 */
	public void setDefault(String defaultValue) {
		getStateHelper().put("default", defaultValue);
	}

	@Override
	public boolean isRequired() {
		// The request parameter is ignored on postbacks, however it's already present in the view scoped bean.
		// So we can safely skip the required validation on postbacks.
		return !isPostback() && super.isRequired();
	}

	// Inner classes --------------------------------------------------------------------------------------------------

	private class AttributeInterceptMap extends MapWrapper<String, Object> {

		private static final long serialVersionUID = -7674000948288609007L;

		private AttributeInterceptMap(Map<String, Object> map) {
			super(map);
		}

		@Override
		public Object get(Object key) {
			Object value = super.get(key);

			if (Utils.isEmpty(value) && "label".equals(key)) {

				// Next check if our outer component has a value expression for the label
				ValueExpression labelExpression = ViewParam.this.getValueExpression("label");
				if (labelExpression != null) {
					value = labelExpression.getValue(getELContext());
				}

				// No explicit label defined, default to "name" (which is in many cases the most sane label anyway).
				if (value == null) {
					value = ViewParam.this.getName();
				}
			}

			return value;
		}

	}

}