tuple.java

一个简单的数据库

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package database;
import java.io.*;
import java.util.ArrayList;
/**
 *
 * @author outlaw
 */
public class Tuple implements Serializable{
    String[] values;
    
    public Tuple(String[] vals)
    {
        int len=vals.length;
        values=new String[len];
        for(int i=0;i<len;i++)
        {
            values[i]=vals[i];
        }
    }
    public Comparable getValue(int attribID,String type)
    {
        String value=values[attribID];
        if(type.equals("int"))
            return Integer.parseInt(value);
        if(type.equals("float"))
            return Float.parseFloat(value);
        if(type.startsWith("char"))
            return value;
        return null;
    }
    public Tuple(byte[] data,String[] types) throws Exception
    {
        ByteArrayInputStream bais=new ByteArrayInputStream(data);
        DataInputStream dis=new DataInputStream(bais);
        int len=types.length;
        values=new String[len];
        for(int i=0;i<len;i++)
        {
            if(types[i].equals("int"))
            {
                values[i]=String.valueOf(dis.readInt());
            }
            if(types[i].equals("float"))
            {
                values[i]=String.valueOf(dis.readFloat());
            }
            if(types[i].startsWith("char"))
            {
                int realLength=dis.read();
                int maxLen=Integer.parseInt(types[i].substring(4));
                char[] charData=new char[realLength];
                for(int j=0;j<realLength;j++)
                {
                    charData[j]=dis.readChar();
                }
                values[i]=new String(charData);
                dis.skip((maxLen-realLength)*2);
            }
        }
    }
    public byte[] toBytes(String[] types) throws Exception
    {
        ByteArrayOutputStream baos=new ByteArrayOutputStream();
        DataOutputStream dos=new DataOutputStream(baos);
        //int count=0;
        for(int i=0;i<types.length;i++)
        {
            if(types[i].equals("int"))
            {
                dos.writeInt(Integer.parseInt(values[i]));
                //count+=4;
            }
            if(types[i].equals("float"))
            {
                dos.writeFloat(Float.parseFloat(values[i]));
                //count+=4;
            }
            if(types[i].startsWith("char"))
            {
                //这个写入的length在【1，255】之间，是字符的长度，而不是字节的长度
                dos.writeByte(values[i].length());
                dos.writeChars(values[i]);
                int leftLen=Integer.parseInt(types[i].substring(4))-values[i].length();
                //写入多余的没用的bytes
                for(int j=0;j<leftLen*2;j++)
                    dos.writeByte(0);
                //count+=Integer.parseInt(types[i].substring(4))*2+1;
            }
        }
        //System.out.println("Write out"+count+"bytes!");
        //byte[] array=baos.toByteArray();
        //System.out.println("Actually Write out"+array.length+"bytes!");
        dos.close();        
        return baos.toByteArray();
    }
    public String[] getValues()
    {
        return values;
    }
    @Override
    public String toString()
    {
        StringBuilder builder=new StringBuilder();
        builder.append("[");
        for(int i=0;i<values.length-1;i++)
        {
            builder.append(values[i]+",");
        }
        builder.append(values[values.length-1]+"]");
        
        return builder.toString();
    }
}