msgblockiterator.java

cwbbs 云网论坛源码

package com.redmoon.forum;


public class MsgBlockIterator {
    
    
    String groupKey;

    private long[] infoBlock;

    private long blockID;
    private long blockStart;

    private String query;

    private long startIndex;
    private long currentIndex;
    private long endIndex;


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

    
    protected MsgBlockIterator(long[] threadBlock, String query,
                               String groupKey,
                               long startIndex, long endIndex) {
        this.infoBlock = threadBlock;
        this.blockID = startIndex / MsgCache.MSG_BLOCK_SIZE;
        this.blockStart = blockID * MsgCache.MSG_BLOCK_SIZE;
        this.query = query;
        this.currentIndex = startIndex - 1;
        this.startIndex = startIndex;
        this.endIndex = endIndex;
        this.groupKey = groupKey;
    }

    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 != Long.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(long index) {
        if (index < 0) {
            return null;
        }
        
        
        if (index < blockStart || index >= blockStart + MsgCache.MSG_BLOCK_SIZE) {
            
            MsgCache mc = new MsgCache();
            this.infoBlock = mc.getMsgBlock(query, groupKey, index);
            this.blockID = index / MsgCache.MSG_BLOCK_SIZE;
            this.blockStart = blockID * MsgCache.MSG_BLOCK_SIZE;
        }
        Object element = null;
        
        
        int relativeIndex = (int) (index % MsgCache.MSG_BLOCK_SIZE);
        
        if (relativeIndex < infoBlock.length) {
            MsgMgr msgmgr = new MsgMgr();
            element = msgmgr.getMsgDb(infoBlock[relativeIndex]);
        }
        return element;
    }
}