org.omnifaces.converter.ValueChangeConverter Maven / Gradle / Ivy
/*
* Copyright 2020 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
*
* https://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.converter;
import java.util.Objects;
import javax.faces.component.EditableValueHolder;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.convert.Converter;
/**
*
* By default, JSF converters run on every request, regardless of whether the submitted value has changed or not. In
* case of conversion against the DB on complex objects which are already stored in the model in a broader scope, such
* as the view scope, this may result in unnecessarily expensive service/DAO calls. In such case, you'd like to perform
* the expensive service/DAO call only when the submitted value is really changed as compared to the model value.
*
* This converter offers you a template to do it transparently. To use it, just change your converters from:
*
* public class YourConverter implements Converter<YourEntity> {
*
* public YourEntity getAsObject(FacesContext context, UIComponent component, String submittedValue) {
* // ...
* }
*
* // ...
* }
*
* to
*
* public class YourConverter extends ValueChangeConverter<YourEntity> {
*
* public YourEntity getAsChangedObject(FacesContext context, UIComponent component, String submittedValue) {
* // ...
* }
*
* // ...
* }
*
*
* So, essentially, just replace implements Converter by extends ValueChangeConverter and
* rename the method from getAsObject to getAsChangedObject.
* Note: the getAsString method of your converter doesn't need to be changed.
*
* @author Bauke Scholtz
* @since 1.6
*/
public abstract class ValueChangeConverter implements Converter {
/**
* If the component is an instance of {@link EditableValueHolder} and the string representation of its old object
* value is equal to the submitted value, then immediately return its old object value unchanged. Otherwise, invoke
* {@link #getAsChangedObject(FacesContext, UIComponent, String)} which may in turn do the necessary possibly
* expensive DAO operations.
* @throws ClassCastException When T is of wrong type.
*/
@Override
@SuppressWarnings("unchecked")
public T getAsObject(FacesContext context, UIComponent component, String submittedValue) {
if (component instanceof EditableValueHolder) {
String newStringValue = submittedValue;
T oldObjectValue = (T) ((EditableValueHolder) component).getValue();
String oldStringValue = getAsString(context, component, oldObjectValue);
if (Objects.equals(newStringValue, oldStringValue)) {
return oldObjectValue;
}
}
return getAsChangedObject(context, component, submittedValue);
}
/**
* Use this method instead of {@link #getAsObject(FacesContext, UIComponent, String)} if you intend to perform the
* conversion only when the submitted value is really changed as compared to the model value.
* @param context The involved faces context.
* @param component The involved UI component.
* @param submittedValue The submitted value.
* @return The converted value, exactly like as when you use {@link #getAsObject(FacesContext, UIComponent, String)}
* the usual way.
*/
public abstract T getAsChangedObject(FacesContext context, UIComponent component, String submittedValue);
}