charnode.java

支持并发访问的B+树

/*
 * Created on Aug 1, 2004
 *
 * TODO To change the template for this generated file go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
package com.nay0648.ds.bplustree;
import java.nio.*;
import java.util.*;

/**
 * Description:<br>
 * @abstract
 * @keywords
 * @author nay0648
 * @version last modified:Jun 6, 2004
 */
class CharNode extends BPlusTreeNode
{
	public CharNode()
	{
		super();
	}

	/**
	 * get a new empty char node instance
	 * @param addr
	 * file pointer point to this node
	 * @return
	 */
	public BPlusTreeNode getInstance(long addr)
	{
		BPlusTreeNode node;
		
		node=new CharNode();
		node.setAddr(addr);
		return node;
	}
	
	/**
	 * rebuild the char node instance from byte array
	 * @param addr
	 * file pointer point to this node
	 * @param node
	 * byte array contain this node's information
	 * @return
	 */
	public BPlusTreeNode getInstance(long addr,byte[] node)
	{
		int i,j,valid;
		byte[] key;
		ByteBuffer buff;
		CharNode cnode;
		List keyword,pointer;
		
		//check argument size
		if(node.length!=CharNode.nodelength)
		throw new IllegalArgumentException("byte array's length mismatch. array length: "+node.length+" required: "+CharNode.nodelength);
		//construct buffer
		buff=ByteBuffer.wrap(node);
		//prepare to read data from buffer
		buff.position(0);
		buff.limit(buff.capacity());
		cnode=new CharNode();//build a new empty node
		cnode.setAddr(addr);//set file pointer
		//read data in order
		if(buff.get()==CharNode.TRUE) cnode.isLeaf(true);else cnode.isLeaf(false);
		valid=buff.getInt();
		//keyword and pointer list
		keyword=new ArrayList();
		pointer=new ArrayList();
		key=new byte[CharNode.keywordlength];
		/*
		 * if this is a empty node,it still contain one pointer
		 */
		for(i=0;i<valid;i++)
		{
			pointer.add(new Long(buff.getLong()));
			buff.get(key);
			keyword.add(new CharKeyword(key,CharNode.keywordlength));//here use the keyword's Keyword form
		}
		//read the last pointer
		pointer.add(new Long(buff.getLong()));
		//set keyword and pointer list
		cnode.setKeywordList(keyword);
		cnode.setPointerList(pointer);
		return cnode;
	}
	
	/**
	 * get the node's binary byte array,used to save node into file
	 * @return
	 */
	public byte[] getBytes()
	{
		int i;
		ByteBuffer buff;

		buff=ByteBuffer.allocate(CharNode.nodelength);
		//write data into buffer in order
		if(this.isLeaf()) buff.put(IntNode.TRUE);else buff.put(IntNode.FALSE);
		buff.putInt(this.getValid());//valid keyword number
		for(i=0;i<this.getValid();i++)
		{
			buff.putLong(this.getPointer(i));
			buff.put(((CharKeyword)this.getKeyword(i)).getBytes());
		}
		/*
		 * if this is a empty node,it still contain one pointer
		 */
		buff.putLong(this.getLast());//the last pointer
		return buff.array();
	}
	
	/**
	 * convert a keyword from Object form to Keyword form
	 * @param o
	 * the keyword's Object form
	 */
	public Keyword buildKeyword(Object o)
	{
		return new CharKeyword((String)o,CharNode.keywordlength);
	}
	
	/**
	 * this is used to convert a kwyword's byte array form to the 
	 * Keyword form,it is used when keyword is received from remote
	 * host
	 * @param key
	 * keyword's byte array form
	 * @return
	 * keyword's Keyword form
	 */
	public Keyword buildKeyword(byte[] key)
	{
		return new CharKeyword(key,CharNode.keywordlength);
	}
}