Reading/Writing Integer Bytes

[AndrewM16921]

Hi, a piece of my recent program includes generating map "chunks" and saving each chunk as a .chunk file. In the past, I typically stored such data as text in the file, but it has come to a point where I need to optimize the file size by writing the individual integer bytes to a file rather than writing/reading strings then parsing them. Not really sure how to do this though... any help appreciated, thanks.

Edit: Actually, better yet, just reading/writing individual bytes would be sufficient.

This is what I tried to do... but it just prints the bytes as strings to the file, and tries to read it as text (see error message).

Exception in thread "main" java.util.InputMismatchException: Value out of range. Value:"0123456789" Radix:10
at java.util.Scanner.nextByte(Unknown Source)
at java.util.Scanner.nextByte(Unknown Source)
at MapEditor.IOTest.loadBytes(IOTest.java:44)
at MapEditor.IOTest.main(IOTest.java:21)

package MapEditor;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;

public class IOTest
{
	private static final String sep = File.separator;
	
	public static void main(String[] args)
	{
		byte[] someBytes = new byte[10];
		for(byte i = 0; i < 10; i++)
		{
			someBytes[i] = i;
		}
		saveBytes(someBytes);
		someBytes = loadBytes();
		for(int i = 0; i < 10; i++)
		{
			System.out.println(someBytes[i]);
		}
	}
	
	private static byte[] loadBytes()
	{
		String fileName = "data" + sep + "test.dat";
		Scanner reader;
		File file = new File(fileName);
		try
		{
			reader = new Scanner(file);
		}
		catch(FileNotFoundException ex)
		{
			return null;
		}
		byte[] bytes = new byte[(int)file.length()];
		for(int i = 0; i < bytes.length; i++)
		{
			bytes[i] = reader.nextByte();
		}
		
		return bytes;
	}
	
	private static boolean saveBytes(byte[] bytes)
	{
		String fileName = "data" + sep + "test.dat";
		File file = new File(fileName);
		PrintWriter writer = null;
		try
		{
			writer = new PrintWriter(file);
		}
		catch(FileNotFoundException ex1)
		{
			try
			{
				file.createNewFile();
				writer = new PrintWriter(file);
			}
			catch(IOException ex2)
			{
				System.err.println("Could not create new file (" + fileName + ") Error: " + ex2);
				return false;
			}
		}
		
		for(int i = 0; i < bytes.length; i++)
		{
			writer.print(bytes[i]);
		}
		writer.flush();
		writer.close();
		return true;
	}
}

[Jodokus]

A few remarks:
- What is the range of the integers you’re trying to store in bytes? Is the "map" a picture, are you saving pixels? An integer is 32 bits, a byte is 8 bits.
If you cast a byte to an integer (what you are implicitly doing if you use it as a counter in a for-loop) it wraps to negative –128 (range byte: -128 to 127). So it’s a bad idea to use a byte as a counter using a realistic (>10) range.
- You use Scanner. I’m a very old-fashioned programmer not using it very much, but I think to know that it is used for delimited text, not a bytestream.
- You use PrintWriter. It produces human-readable textfiles, That human can’t figure out where integers larger then 10 stop and start again without delimiters (Sorry, I suppose you figured out the last two points already but used it for the example)
- If I was going to help you, my knowledge would come from Thinking in Java from Bruce Eckel. The 3rd Edition is free on the internet (Bruce Eckel's MindView, Inc: Free Electronic Book: Thinking in Java, 3rd Edition), chapter 12 is on IO.)

I guess you need a Data in/outputstream, wrapped by buffered- and filestreams.