Copying Binary File using BufferInputStream and Bufferoutputstream, ensuring that the correct number of bytes are written

App.java

package com.deltastateonline.files;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class App {

	public App() {
		// TODO Auto-generated constructor stub
	}

	public static void main(String[] args) throws IOException  {
		// TODO Auto-generated method stub
		
		String infile = "data\\in\\IMG_2004.JPG";
		
		File aFile = new File(infile);
		
		//int  BUFFER_SIZE = 8 * 1024;
		int  BUFFER_SIZE = 2 * 1024;
		
		long totalLenght = aFile.length();
		
		
		String outfile =  String.format("data\\out.1\\IMG_2004.%s.JPG",BUFFER_SIZE) ;
		BufferedInputStream inputStream = null ; 
		BufferedOutputStream outStream = null ; 		
		
		
		System.out.println("Buffer Size : "+BUFFER_SIZE);
		
		byte[] buffer = new byte[BUFFER_SIZE];
		
		try {
			inputStream = new BufferedInputStream(new FileInputStream(infile));
			outStream = new BufferedOutputStream(new FileOutputStream(outfile));
			
			int acc = 0;
			
			while(inputStream.read(buffer) != -1){	
				
				//
				if((acc+BUFFER_SIZE) < totalLenght){
					outStream.write(buffer);
				}else{
					long diff =  totalLenght - acc;	// howmany bytes are left to be written
					outStream.write(buffer, 0, (int)diff); // only write the remaining bytes
				}
				
				acc = acc + BUFFER_SIZE; // increase the accumulator
			}
			
			outStream.flush();		
			
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally{
			
			if(inputStream != null){
				inputStream.close();
			}
			
			if(outStream != null){
				outStream.close();
			}
		}	

	}

}

Using the naive solutions found on the internet, copying files result in f having more bytes than they should.
The output below shows a file been copied with different buffer sizes. The file names are IMG_2004.{BUFFER_SIZE}.jpg.
For some image files and text based files, this doesn't matter but it does matter for pdf files.