String getFileContents(String fileName) throws Exception {
    File theFile = new File(fileName);
    byte[] bytes = new byte[(int) theFile.length()];
    InputStream in = new FileInputStream(theFile);
    int m = 0, n = 0;
    while (m < bytes.length) {
	n = in.read(bytes, m, bytes.length - m);
	m += n;
    }
    in.close();
    
    // using default encoding, this is probably what BufferedReader.readLine does anyway
    return new String(bytes); 
}

import java.io.FileInputStream;
import java.nio.channels.FileChannel;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;

public class ReadWholeFile2 {
    public static void main(String[] args) throws Exception {
	String contents = getFileContents("test.txt");
	System.out.println(contents);
    }

    static String getFileContents(String fileName) throws Exception {
	FileInputStream fin = new FileInputStream(fileName);
	FileChannel fch = fin.getChannel();

	// map the contents of the file into ByteBuffer
	ByteBuffer byteBuff = fch.map(FileChannel.MapMode.READ_ONLY, 0, fch.size());

	// convert ByteBuffer to CharBuffer
	// CharBuffer chBuff = Charset.defaultCharset().decode(byteBuff);
	CharBuffer chBuff = Charset.forName("UTF-8").decode(byteBuff);
	return chBuff.toString();
    }
}