Adding Extended Characters to Java Properties File

Recently, I was updating the copyrights text in amConsole.properties.
the copyrights text contains extended ASCII characters because part
of the copyrights/license is in France.

Java Properties file cannot have extended ASCII characters, we need to
have them in Hex e.g. \u00e0 for à

Here is a small program that converted extended ASCII characters to
Hex.

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;

public class StringToHex {
    private static String charToHex(char c) {
        StringBuffer buffer = new StringBuffer();
        if (c <= 0x7E) {
            buffer.append(c);
        } else {
            buffer.append("\\u");
            String hex = Integer.toHexString(c);
            for (int j = hex.length(); j < 4; j++ ) {
                buffer.append('0');
            }
            buffer.append(hex);
        }
        return buffer.toString();
    }

    private static String readInput(String fileName) {
        StringBuffer buffer = new StringBuffer();
        try {
            FileInputStream fis = new FileInputStream(fileName);
            InputStreamReader isr = new InputStreamReader(fis, "UTF8");
            Reader in = new BufferedReader(isr);
            int ch;
            while ((ch = in.read()) > -1) {
                buffer.append(charToHex((char)ch));
            }
            in.close();
            return buffer.toString();
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
    }

    public static void main(String[] args) {
        if (args.length != 1) {
            System.err.println("Usage: java StringToHex ");
            System.exit(1);
        }

        String inputString = readInput(args[0]);
        if (inputString != null) {
            System.out.println(inputString);
        }
        System.exit(0);
    }
}