Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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.apache.wicket.feedback; import java.util.List; import org.apache.wicket.Component; import org.apache.wicket.MetaDataKey; import org.apache.wicket.Session; import org.apache.wicket.markup.html.panel.FeedbackPanel; /** * A specialized feedback panel that only displays messages from inside a fence defined by a * container component. Instances will not show messages coming from inside a nested fence, allowing * the nesting of these panels to work correctly without displaying the same feedback message twice. * A constructor that does not takes a fencing component creates a catch-all panel that shows * messages that do not come from inside any fence or from the {@link Session}. * <p/> * <h2>IN DEPTH EXPLANATION</h2> * <p> * It is often very useful to have feedback panels that show feedback that comes from inside a * certain container only. For example given a page with the following structure: * </p> * <p/> * <pre> * Page * Form1 * Feedback1 * Input1 * Form2 * Feedback2 * Input2 * </pre> * <p> * we want Feedback2 to show messages originating only from inside Form2 and Feedback1 to show * messages only originating from Form1 but not Form2 (because messages originating from Form2 are * already shown by Feedback2). * </p> * <p> * It is fairly simple to configure Feedback2 - a {@link ContainerFeedbackMessageFilter} added to * the regular {@link FeedbackPanel} will do the trick. The hard part is configuring Feedback1. We * can add a {@link ContainerFeedbackMessageFilter} to it, but since Form2 is inside Form1 the * container filter will allow messages from both Form1 and Form2 to be added to FeedbackPanel1. * </p> * <p> * This is where the {@link FencedFeedbackPanel} comes in. All we have to do is to make * FeedbackPanel2 a {@link FencedFeedbackPanel} with the fencing component defined as Form2 and * Feedback1 a {@link FencedFeedbackPanel} with the fencing component defined as Form1. * {@link FencedFeedbackPanel} will only show messages that original from inside its fencing * component and not from inside any descendant component that acts as a fence for another * {@link FencedFeedbackPanel}. * </p> * <p> * When created with a {@code null} fencing component or using a constructor that does not take one * the panel will only display messages that do not come from inside a fence. It will also display * messages that come from {@link Session}. This acts as a catch-all panels showing messages that * would not be shown using any other instance of the {@link FencedFeedbackPanel} created with a * fencing component. There is usually one instance of such a panel at the top of the page to * display notifications of success. * </p> * * @author igor */ public class FencedFeedbackPanel extends FeedbackPanel { private static final long serialVersionUID = 1L; private static final MetaDataKey<Integer> FENCE_KEY = new MetaDataKey<Integer>() { private static final long serialVersionUID = 1L; }; private final Component fence; /** * Creates a catch-all feedback panel that will show messages not coming from any fence, * including messages coming from {@link Session} * * @param id */ public FencedFeedbackPanel(String id) { this(id, (Component) null); } /** * Creates a feedback panel that will only show messages if they original from, or inside of, * the {@code fence} component and not from any inner fence. * * @param id * @param fence */ public FencedFeedbackPanel(String id, Component fence) { this(id, fence, null); } /** * Creates a catch-all instance with a filter. * * @param id * @param filter * @see #FencedFeedbackPanel(String) */ public FencedFeedbackPanel(String id, IFeedbackMessageFilter filter) { this(id, null, filter); } /** * Creates a fenced feedback panel with a filter. * * @param id * @param fence * @param filter * @see #FencedFeedbackPanel(String, Component) */ public FencedFeedbackPanel(String id, Component fence, IFeedbackMessageFilter filter) { super(id, filter); this.fence = fence; if (fence != null) { incrementFenceCount(); } } private void incrementFenceCount() { Integer count = fence.getMetaData(FENCE_KEY); count = count == null ? 1 : count + 1; fence.setMetaData(FENCE_KEY, count); } @Override protected void onRemove() { super.onRemove(); if (fence != null) { // decrement the fence count decrementFenceCount(); } } private void decrementFenceCount() { Integer count = fence.getMetaData(FENCE_KEY); count = (count == null || count == 1) ? null : count - 1; fence.setMetaData(FENCE_KEY, count); } @Override protected FeedbackMessagesModel newFeedbackMessagesModel() { return new FeedbackMessagesModel(this) { private static final long serialVersionUID = 1L; @Override protected List<FeedbackMessage> collectMessages(Component panel, IFeedbackMessageFilter filter) { if (fence == null) { // this is the catch-all panel return new FencedFeedbackCollector(panel.getPage(), true).collect(filter); } else { // this is a fenced panel return new FencedFeedbackCollector(fence, false).collect(filter); } } }; } @Override protected void onReAdd() { if (this.fence != null) { // The fence mark is removed when the feedback panel is removed from the hierarchy. // see onRemove(). // when the panel is re-added, we recreate the fence mark. incrementFenceCount(); } super.onReAdd(); } private final class FencedFeedbackCollector extends FeedbackCollector { private FencedFeedbackCollector(Component component, boolean includeSession) { super(component, includeSession); } @Override protected boolean shouldRecurseInto(Component component) { return !componentIsMarkedAsFence(component); } private boolean componentIsMarkedAsFence(Component component) { return component.getMetaData(FENCE_KEY) != null; } } }