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The MyFaces Commons Subproject provides base classes for usage in both the MyFaces implementation and the MyFaces Tomahawk components. This is also a general set of utility classes for usage in your JSF projects independent of the implementation you might be deciding upon.
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/*
 * Copyright 2005 The Apache Software Foundation.
 *
 * 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.apache.myfaces.util;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;

import javax.faces.component.UIComponent;
import javax.faces.component.UISelectItem;
import javax.faces.component.UISelectItems;
import javax.faces.el.ValueBinding;
import javax.faces.model.SelectItem;

import org.apache.myfaces.renderkit.RendererUtils;

/**
 * @author Mathias Broekelmann (latest modification by $Author$)
 * @version $Revision$ $Date$
 */
public class SelectItemsIterator implements Iterator
{
    private final Iterator _childs;
    private Iterator _nestedItems;
    private Object _nextItem;
    private String _collectionLabel;
    private UISelectItems _currentUISelectItems;

    public SelectItemsIterator(UIComponent selectItemsParent)
    {
        _childs = selectItemsParent.getChildren().iterator();
    }

    public boolean hasNext()
    {
        if(_nextItem != null)
        {
            return true;
        }
        if(_nestedItems != null)
        {
            if(_nestedItems.hasNext())
            {
                return true;
            }
            _nestedItems = null;
        }            
        if (_childs.hasNext())
        {
            UIComponent child = (UIComponent) _childs.next();
            if (child instanceof UISelectItem)
            {
                UISelectItem uiSelectItem = (UISelectItem) child;
                Object item = uiSelectItem.getValue();
                if (item == null)
                {
                    Object itemValue = ((UISelectItem) child).getItemValue();
                    String label = ((UISelectItem) child).getItemLabel();
                    String description = ((UISelectItem) child)
                                    .getItemDescription();
                    boolean disabled = ((UISelectItem) child).isItemDisabled();
                    if (label == null)
                    {
                        label = itemValue.toString();
                    }
                    item = new SelectItem(itemValue, label, description,
                                    disabled);
                }
                else if (!(item instanceof SelectItem))
                {
                    ValueBinding binding = ((UISelectItem) child)
                                    .getValueBinding("value");
                    throw new IllegalArgumentException(
                                    "Value binding '"
                                    + (binding == null ? null : binding.getExpressionString())
                                    + "' of UISelectItem : "
                                    + RendererUtils.getPathToComponent(child)
                                    + " does not reference an Object of type SelectItem");
                }
                _nextItem = item;
                return true;
            }
            else if (child instanceof UISelectItems)
            {
                _currentUISelectItems = ((UISelectItems) child);
                Object value = _currentUISelectItems.getValue();

                if (value instanceof SelectItem)
                {
                    _nextItem = value;
                    return true;
                }
                else if (value instanceof SelectItem[])
                {
                    _nestedItems = Arrays.asList((SelectItem[]) value)
                                    .iterator();
                    _collectionLabel = "Array";
                    return hasNext();
                }
                else if (value instanceof Collection)
                {
                    _nestedItems = ((Collection)value).iterator();
                    _collectionLabel = "Collection";
                    return hasNext();
                }
                else if (value instanceof Map)
                {
                    Map map = ((Map) value);
                    Collection items = new ArrayList(map.size()); 
                    for (Iterator it = map.entrySet().iterator(); it
                                    .hasNext();)
                    {
                        Map.Entry entry = (Map.Entry) it.next();
                        items.add(new SelectItem(entry.getValue(), entry
                                        .getKey().toString()));
                    }
                    _nestedItems = items.iterator();
                    _collectionLabel = "Map";
                    return hasNext();
                }
                else
                {
                    ValueBinding binding = _currentUISelectItems.getValueBinding("value");

                    throw new IllegalArgumentException(
                        "Value binding '"
                        + (binding == null ? null : binding
                                        .getExpressionString())
                        + "'of UISelectItems with component-path "
                        + RendererUtils.getPathToComponent(child)
                        + " does not reference an Object of type SelectItem, SelectItem[], Collection or Map but of type : "
                        + ((value == null) ? null : value
                                        .getClass()
                                        .getName()));
                }
            }
            else
            {
                //todo: may other objects than selectItems be nested or not?
                //log.error("Invalid component : " + getPathToComponent(child) + " : must be UISelectItem or UISelectItems, is of type : "+((child==null)?"null":child.getClass().getName()));
            }
        }
        return false;
    }

    public Object next()
    {
        if (!hasNext())
        {
            throw new NoSuchElementException();
        }
        if(_nextItem != null)
        {
            Object value = _nextItem;
            _nextItem = null;
            return value;
        }        
        if (_nestedItems != null)
        {
            Object item = _nestedItems.next();
            if (!(item instanceof SelectItem))
            {
                ValueBinding binding = _currentUISelectItems
                                .getValueBinding("value");
                throw new IllegalArgumentException(
                _collectionLabel + " referenced by UISelectItems with binding '"
                + binding.getExpressionString()
                + "' and Component-Path : " + RendererUtils.getPathToComponent(_currentUISelectItems)
                + " does not contain Objects of type SelectItem");
            }
            return item;
        }
        throw new NoSuchElementException();
    }

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