mergeiteratorfilter.java

webwork source

/*
 * WebWork, Web Application Framework
 *
 * Distributable under Apache license.
 * See terms of license at opensource.org
 */
package webwork.util;

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

/**
 *	A bean that takes several iterators and outputs the merge of them.
 *
 *	@author Rickard 謆erg ([e-mail])
 *	@version $Revision: 1.7 $
 */
public class MergeIteratorFilter
   extends IteratorFilterSupport
   implements java.util.Iterator, webwork.action.Action
{
   // Attributes ----------------------------------------------------
   List sources = new ArrayList();
   List iterators = 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.");
   }
}