How do I encode decode UTF-16LE byte arrays with a BOM

Question

UTF-16 byte arrays must be encoded and decoded into and out of java.lang.String. I've been handed byte arrays with a byte order marker (BOM), and I need to encrypt them with a BOM.

Additionally, I'd like to emit the encoding in little endian (together with the LE BOM) since I'm working with a Microsoft client/server to prevent any misunderstandings. Although I am aware that the BOM should operate big endian, I don't want to go against the grain in the Windows environment.

Here is a method that encodes a java.lang as an illustration. Little endian, UTF-16 string with a BOM:

public static byte[] encodeString(String message) {

    byte[] tmp = null;
    try {
        tmp = message.getBytes("UTF-16LE");
    } catch(UnsupportedEncodingException e) {
        // should not possible
        AssertionError ae =
        new AssertionError("Could not encode UTF-16LE");
        ae.initCause(e);
        throw ae;
    }

    // use brute force method to add BOM
    byte[] utf16lemessage = new byte[2 + tmp.length];
    utf16lemessage[0] = (byte)0xFF;
    utf16lemessage[1] = (byte)0xFE;
    System.arraycopy(tmp, 0,
                     utf16lemessage, 2,
                     tmp.length);
    return utf16lemessage;
}

How should I approach this in Java? In a perfect world, I wouldn't want to transfer the entire byte array into a new one that has two more bytes created at the start.

The same is true for decoding such a string, however java.lang makes this process considerably simpler.

public String(byte[] bytes,
              int offset,
              int length,
              String charsetName)