import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class MemoryMappedFile {

	private String deviceName; // initialise to peripheral name
	private String filename; // initialise to peripheral buffer file name
	
	public MemoryMappedFile (String deviceName, String filename) {
		if (deviceName != null)
			this.setDeviceName(deviceName);
		else
			this.setDeviceName("");
		
		if (filename != null)
			this.filename = filename;
		else
			this.filename = "largeFile.txt";
	}
	
	public int write (int position, int size, Byte[] bytesBuffer) {
		int count = 0;
		RandomAccessFile memoryMappedFile;
		try {
			memoryMappedFile = new RandomAccessFile(this.filename, "rw");

			//Mapping a file into memory
	
			MappedByteBuffer out = memoryMappedFile.getChannel().map(FileChannel.MapMode.READ_WRITE, position, size);
			
			//Writing into Memory Mapped File
			for (int i = 0; i < size; i++) {
				if (i<bytesBuffer.length) {
					out.put(bytesBuffer[i]);
					count ++;
				}
				else
					break;
			}
	
			System.out.println("Writing to Memory Mapped File " + count + " bytes is completed");
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}		
		return count;		
	}
	
	public Byte[] read (int position, int size) {
		Byte[] data = new Byte[size];
		RandomAccessFile memoryMappedFile;
		try {
			memoryMappedFile = new RandomAccessFile(this.filename, "rw");
		

			//Mapping a file into memory
	
			MappedByteBuffer in = memoryMappedFile.getChannel().map(FileChannel.MapMode.READ_ONLY, position, size);
			//reading from memory file in Java
			for (int i = 0; i < size ; i++) {
				data[i] = in.get(i);
				System.out.print((char) in.get(i));
			}
			System.out.println("Reading from Memory Mapped File is completed");
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}	
		return data;
	}

	public String getDeviceName() {
		return deviceName;
	}

	public void setDeviceName(String deviceName) {
		this.deviceName = deviceName;
	}
}