bufferedmanager.java

一个简单的数据库

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package bufferedManager;
import database.*;
import java.util.ArrayList;
import fileManager.*;
import java.io.*;
import catalogManager.*;
/**
 *
 * @author outlaw
 */
public class BufferedManager {
    public static ArrayList<Block> blocks=new ArrayList<Block>();
    public static final int BUFFER_SIZE=100;
            
    public BufferedManager(){
    }
    public static void writeBlocksBack() throws Exception
    {
        Block block=null;
        int len=blocks.size();
        for(int i=0;i<len;i++)
        {
            block=blocks.get(i);
            if(block.dirty)
                FileManager.writeBlockBack(block);
        }
    }
    public static void addBlock(Block block) throws Exception
    {
        block.setDirty();
        rearrange(block);
    }
    public static void rearrange(int index)
    {
        blocks.add(blocks.remove(index));
    }
    public static void rearrange(Block newBlock) throws Exception
    {
        if(blocks.size()>=BUFFER_SIZE)
        {
            Block oldBlock;
            oldBlock=blocks.remove(0);
            if(oldBlock.isDirty())
            {
                
                FileManager.writeBlockBack(oldBlock);
            }
        }
        TableData tb=CatalogManager.getTableByName(newBlock.getTBName());
        tb.setBlockNotInFile(newBlock.getBlockID());
        blocks.add(newBlock);
    }
    public static Block getBlock(TableData tb) throws Exception
    {
        return getBlockFromMemory(tb);
    }
    public static Block getBlockFromMemory(TableData tb) throws Exception
    {
        String tbName=tb.getName();
        int len=blocks.size();
        Block block;
        for(int i=len-1;i>=0;i--)
        {
            block=blocks.get(i);
            if(block.getTBName().equals(tbName)&&!block.isFull())
            {
                rearrange(i);
                return block;
            }
            //如果这个block已经full了，该怎么办。
        }
        block=getBlockFromFile(tb);
        return block;
    }
    public static Block putBlockIntoMemory(TableData tb,int blockID) throws Exception
    {
        try
        {
             RandomAccessFile raf=new RandomAccessFile(tb.getFullName()+".tbl","rw");
             raf.seek(Block.BLOCKSIZE*blockID);
             byte[] data=new byte[Block.BLOCKSIZE];
             raf.read(data);
             Block block=new Block(data,tb.getName(),blockID);
             raf.close();
             return block;
        }catch(Exception ex)
        {
            ex.printStackTrace();
            throw new OperationInfo("Get block for table:["+tb.getName()+"] from file error!");
        }
    }
    public static Block getBlockFromFile(TableData tb) throws Exception
    {
        int len=tb.getBlockNumber();
        Block block=null;
        
        for(int i=0;i<len;i++)
        {
            if(tb.isBlockInFile(i)&&!tb.isBlockFull(i))
            {
                block=putBlockIntoMemory(tb,i);
                tb.setBlockNotInFile(i);
                rearrange(block);
                break;
            }
        }
        return block;
    }
}