Generating a random hex string (of length 50) in Java ME/J2ME

Question

My app needs to generate a hex string to use as a session ID. Java's SecureRandom doesn't seem to be working ("java/lang/NoClassDefFoundError: java/security/SecureRandom: Cannot create class in system package")

I thought of doing something like this:

byte[]  resBuf = new byte[50];
new Random().nextBytes(resBuf);
String  resStr = new String(Hex.encode(resBuf));

But the method nextBytes(byte[] bytes) isn't available for some strange reason.

Does anyone have a means of generating a random hex number in Java ME/J2ME?

Many thanks.

Edit: The above generator seems to work when using Bouncy Castle lcrypto-j2me-145 (but not lcrypto-j2me-147).

Furore

Answer 1

JavaME is a subset of JavaSE, so many classes and methods in the desktop version are not available.

Looks like you are trying to get a random string of a given length. You can do something like this:

    private String getRandomHexString(int numchars){
        Random r = new Random();
        StringBuffer sb = new StringBuffer();
        while(sb.length() < numchars){
            sb.append(Integer.toHexString(r.nextInt()));
        }

        return sb.toString().substring(0, numchars);
    }

Vertu

Since Integer.toHexString strips leading zeroes, the first character of the hex is never zero, except for the rare case where Random.nextInt() returns 0. Instead of Integer.toHexString, one can use String.format("%08x", r.nextInt()). – Nugatory