org.apache.wicket.markup.repeater.ReuseIfModelsEqualStrategy.java Source code

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Here is the source code for org.apache.wicket.markup.repeater.ReuseIfModelsEqualStrategy.java

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/*
 * 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.markup.repeater;

import java.util.Iterator;
import java.util.Map;

import org.apache.wicket.model.IModel;
import org.apache.wicket.util.lang.Generics;

/**
 * Reuse strategy that will reuse an old item if its model is equal to a model inside the newModels
 * iterator. Useful when state needs to be kept across requests for as long as the item is visible
 * within the view.
 * <p>
 * Notice that the <u>model</u> and not the <u>model object</u> needs to implement the
 * {@link #equals(Object)} and {@link #hashCode()} methods. Most of the time it is a good idea to
 * forward the calls to the object, however if a detachable model is used it is often enough to
 * compare an identifier for the object the models are pointing to ( this saves the model from loading the
 * object).
 * 
 * @author Igor Vaynberg (ivaynberg)
 * 
 */
public class ReuseIfModelsEqualStrategy implements IItemReuseStrategy {
    private static final long serialVersionUID = 1L;

    private static IItemReuseStrategy instance = new ReuseIfModelsEqualStrategy();

    /**
     * @return static instance
     */
    public static IItemReuseStrategy getInstance() {
        return instance;
    }

    /**
     * @see org.apache.wicket.markup.repeater.IItemReuseStrategy#getItems(org.apache.wicket.markup.repeater.IItemFactory,
     *      java.util.Iterator, java.util.Iterator)
     */
    @Override
    public <T> Iterator<Item<T>> getItems(final IItemFactory<T> factory, final Iterator<IModel<T>> newModels,
            Iterator<Item<T>> existingItems) {
        final Map<IModel<T>, Item<T>> modelToItem = Generics.newHashMap();
        while (existingItems.hasNext()) {
            final Item<T> item = existingItems.next();
            modelToItem.put(item.getModel(), item);
        }

        return new Iterator<Item<T>>() {
            private int index = 0;

            @Override
            public boolean hasNext() {
                return newModels.hasNext();
            }

            @Override
            public Item<T> next() {
                final IModel<T> model = newModels.next();
                final Item<T> oldItem = modelToItem.get(model);

                final Item<T> item;
                if (oldItem == null) {
                    item = factory.newItem(index, model);
                } else {
                    oldItem.setIndex(index);
                    item = oldItem;
                }
                index++;

                return item;
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }

        };
    }

}