BackwardUniqueIndexIterator.java

00001 /*
00002  * OpenMobileIS - a free Java(TM) Framework for mobile applications Java(TM)
00003  * Copyright (C) 2004-2006 Philippe Delrieu
00004  * All rights reserved.
00005  * Contact: pdelrieu@openmobileis.org
00006  *
00007  * This library is free software; you can redistribute it and/or
00008  * modify it under the terms of the GNU Lesser General Public
00009  * License as published by the Free Software Foundation; either
00010  * version 2.1 of the License, or any later version.
00011  *
00012  * This library is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015  * Lesser General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU Lesser General Public
00018  * License along with this library; if not, write to the Free Software
00019  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
00020  * USA
00021  *
00022  *  Author : Philippe Delrieu
00023  *  
00024  *  Modifications :
00025  *  2004 Creation P.Delrieu
00026  * 
00027  */
00028 
00029 package org.openmobileis.database.fastobjectdb.db;
00030 
00031 import java.io.IOException;
00032 
00033 
00034 import org.openmobileis.database.fastobjectdb.db.exception.FODBException;
00035 import org.openmobileis.database.fastobjectdb.db.index.FODBIndex;
00036 import org.openmobileis.database.fastobjectdb.db.index.FODBUniqueIndex;
00037 import org.openmobileis.database.fastobjectdb.db.index.SearchResult;
00038 import org.openmobileis.database.fastobjectdb.db.index.node.Node;
00039 
00048 public final class BackwardUniqueIndexIterator {
00049         private FODBCollection collection;
00050         private Node currentNode;
00051         private int position = 0;
00052         private boolean begin = false;
00053         private FODBIndex index;
00054 
00058   BackwardUniqueIndexIterator(FODBIndex index, FODBCollection collection) throws IOException, ClassNotFoundException, FODBException {
00059     super();
00060     if (!(index instanceof FODBUniqueIndex))    {
00061         throw new FODBException("Not unique index to iterator awailable");
00062     }
00063     this.collection = collection;
00064     this.index = index;
00065                 collection.getDatabase().getTransactionManager().begin();
00066     try {
00067                         collection.getDatabase().getTransactionManager().enterTransaction(this.collection.getName());
00068         this.currentNode = index.readRoot();
00069         if (this.currentNode.nbKey == 0)        { //empty index
00070                 begin = true;
00071         }
00072         //position at the last element
00073                         this.position = this.currentNode.nbKey-1;
00074                         long childBranch = currentNode.branchs[this.position+1];
00075                         while (childBranch != Node.NO_NODE)     {
00076                                 this.currentNode = (Node)collection.getNodeAtPos(childBranch);
00077                                 this.position = this.currentNode.nbKey-1; 
00078                                 childBranch = currentNode.branchs[this.position+1];
00079                         }
00080     } finally   {
00081                         collection.getDatabase().getTransactionManager().commit();
00082     }
00083   }  
00084   
00085         public boolean hasPrev() throws FODBException   {
00086                 return !begin;
00087         }
00088   
00089         public Object prev() throws FODBException       {
00090                 if (!this.hasPrev()) return null;
00091                 collection.getDatabase().getTransactionManager().begin();
00092                 try     {
00093                         collection.getDatabase().getTransactionManager().enterTransaction(this.collection.getName());
00094                         
00095                         //read current obj
00096                         long objPos= currentNode.ptr[this.position];
00097                         Object ret = collection.getElementAtPos(objPos);
00098                         
00099                         //get next pos
00100                         if (currentNode.branchs[(this.position)] != Node.NO_NODE)       { //goes down
00101                                 long childBranch = currentNode.branchs[this.position];
00102                                 while (childBranch != Node.NO_NODE)     {
00103                                         this.currentNode = (Node)collection.getNodeAtPos(childBranch);
00104                                         this.position = currentNode.nbKey-1; 
00105                                         childBranch = currentNode.branchs[this.position+1];
00106                                 }
00107                         } else  {
00108                                 this.position --;  //goes next
00109                                 while (this.position < 0)       { //goes up
00110                                         long parent = currentNode.parentPtr;
00111                                         if (parent == Node.NO_NODE)     { //root node end index traversal.
00112                                                 begin = true; 
00113                                                 break;
00114                                         }
00115                                         long nodepos = currentNode.filePtr;
00116                                         this.currentNode = (Node)collection.getNodeAtPos(parent);
00117                                         //child node position
00118                                         int i=0;
00119                                         for (; i<this.currentNode.branchs.length; i++)  {
00120                                                 if (nodepos == this.currentNode.branchs[i]) break;
00121                                         }
00122                                         this.position = i-1;
00123                                 }
00124                         }
00125                         
00126                         return ret;
00127                 } finally       {
00128                         collection.getDatabase().getTransactionManager().commit();
00129                 }       
00130         }
00131   
00132         public void initCurrentNode(Object indexKey) throws FODBException       {
00133                 collection.getDatabase().getTransactionManager().begin();
00134                 try     {
00135                         collection.getDatabase().getTransactionManager().enterTransaction(this.collection.getName());
00136                         SearchResult result = ((FODBUniqueIndex)index).getNodeForKey(indexKey);
00137                         if (result.found)       {
00138                                 this.currentNode = result.node;
00139                                 this.position = result.pos;
00140                                 begin = false;
00141                         }
00142                         this.prev(); //position to next record.
00143                 } finally       {
00144                         collection.getDatabase().getTransactionManager().commit();
00145                 }
00146         
00147         }
00148 }

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