trunk/core/src/main/java/org/apache/struts2/util/MergeIteratorFilter.java

/*
 * $Id$
 *
 * Copyright 2006 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.struts2.util;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import com.opensymphony.xwork2.Action;


/**
 * A bean that takes several iterators and outputs the merge of them. Used by 
 * MergeIteratorTag.
 *
 * @see org.apache.struts2.views.jsp.iterator.MergeIteratorTag
 * @see org.apache.struts2.components.MergeIterator
 */
public class MergeIteratorFilter extends IteratorFilterSupport implements Iterator, Action {

    List iterators = new ArrayList();

    // Attributes ----------------------------------------------------
    List sources = new ArrayList();
    int idx = 0;


    // Public --------------------------------------------------------
    public void setSource(Object anIterator) {
        sources.add(anIterator);
    }

    // Action implementation -----------------------------------------
    public String execute() {
        // Make source transformations
        for (int i = 0; i < sources.size(); i++) {
            Object source = sources.get(i);
            iterators.add(getIterator(source));
        }

        return SUCCESS;
    }

    // Iterator implementation ---------------------------------------
    public boolean hasNext() {
        while (iterators.size() > 0) {
            if (((Iterator) iterators.get(idx)).hasNext()) {
                return true;
            } else {
                iterators.remove(idx);

                if (iterators.size() > 0) {
                    idx = idx % iterators.size();
                }
            }
        }

        return false;
    }

    public Object next() {
        try {
            return ((Iterator) iterators.get(idx)).next();
        } finally {
            idx = (idx + 1) % iterators.size();
        }
    }

    public void remove() {
        throw new UnsupportedOperationException("Remove is not supported in MergeIteratorFilter.");
    }
}