objectblockiterator.java

来自「cwbbs 云网论坛源码」· Java 代码 · 共 205 行

package com.cloudwebsoft.framework.base;

import org.apache.log4j.Logger;
import java.util.Iterator;

public class ObjectBlockIterator implements Iterator {
    public ObjectBlockIterator() {
        try {
            jbInit();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    public Logger logger = Logger.getLogger(this.getClass().getName());

    ObjectDb objectDb;

    private Object[] infoBlock;
    private int blockID;
    private int blockStart;

    private String query;

    private int startIndex;
    private int currentIndex;
    private int endIndex;

    private Object previousElement = null;
    private Object nextElement = null;

    String groupKey;

    
    public ObjectBlockIterator(ObjectDb objectDb, Object[] block, String query,
                               String groupKey,
                               int startIndex, int endIndex) {
        this.objectDb = objectDb;
        this.infoBlock = block;
        this.blockID = startIndex / objectDb.getBlockSize();
        this.blockStart = blockID * objectDb.getBlockSize();
        this.query = query;
        this.currentIndex = startIndex - 1;
        this.startIndex = startIndex;
        this.endIndex = endIndex;
        this.groupKey = groupKey;
    }

    public void remove() {

    }

    public boolean hasNext() {
        
        
        if (currentIndex == endIndex) {
            return false;
        }
        
        
        
        if (nextElement == null) {
            nextElement = getNextElement();
            

            
            if (nextElement == null) {
                return false;
            }
        }
        return true;
    }

    public boolean hasPrevious() {
        
        if (currentIndex == startIndex) {
            return false;
        }
        
        
        if (previousElement == null) {
            previousElement = getPreviousElement();
            
            if (previousElement == null) {
                return false;
            }
        }
        return true;
    }

    public Object next() throws java.util.NoSuchElementException {
        Object element = null;
        if (nextElement != null) {
            element = nextElement;
            this.nextElement = null;
        } else {
            element = getNextElement();
            if (element == null) {
                throw new java.util.NoSuchElementException();
            }
        }
        
        return element;
    }

    public Object previous() {
        Object element = null;
        if (previousElement != null) {
            element = previousElement;
            previousElement = null;
        } else {
            element = getPreviousElement();
            if (element == null) {
                throw new java.util.NoSuchElementException();
            }
        }
        return element;
    }

    
    private Object getNextElement() {
        previousElement = null;
        Object element = null;
        if (endIndex != Integer.MAX_VALUE) { 
            while (currentIndex + 1 < endIndex && element == null) {
                currentIndex++;
                element = getElement(currentIndex);
                if (element == null)
                    break;
                
            }
        } else { 
            if (currentIndex + 1 < endIndex) {
                currentIndex++;
                element = getElement(currentIndex);
            }
        }
        
        return element;
    }

    / 当endIndex受攻击很大时，就会使得循环计算很长时间，因此改为当element为null时退出
     private Object getNextElement() {
       previousElement = null;
       Object element = null;
       if (endIndex!=Integer.MAX_VALUE) { 
         while (currentIndex + 1 < endIndex && element == null) {
           currentIndex++;
           element = getElement(currentIndex);
           
         }
       }
       else { 
         if (currentIndex + 1 < endIndex) {
           currentIndex++;
           element = getElement(currentIndex);
         }
       }
       
       return element;
     }
    */

   
   private Object getPreviousElement() {
       nextElement = null;

       Object element = null;
       while (currentIndex >= startIndex && element == null) {
           currentIndex--;
           element = getElement(currentIndex);
       }
       return element;
   }

    
    private Object getElement(int index) {
        
        if (index < 0) {
            return null;
        }
        
        
        if (index < blockStart || index >= blockStart + objectDb.getBlockSize()) {
            
            this.infoBlock = objectDb.getObjectBlock(query, groupKey, index);
            this.blockID = index / objectDb.getBlockSize();
            this.blockStart = blockID * objectDb.getBlockSize();
        }
        Object element = null;
        
        
        int relativeIndex = index % objectDb.getBlockSize();
        
        if (relativeIndex < infoBlock.length) {
            element = objectDb.getObjectDb(infoBlock[relativeIndex]);
            
        }
        return element;
    }

    private void jbInit() throws Exception {
    }
}