How store hexadecimal strings in a Byte array? [duplicate]

I need help to create the header as explain below, I am not confident with byte conversion and big endian convention.

I think my problem comes from the lines byte[] VERSION = "01".getBytes(); I don't know how to 'force' the String to be stored in one byte.

Header creation

public static final int HEADER_SIZE = 8;
byte[] header = new byte[HEADER_SIZE];

// Header struture
/*
*byte 0   : Version
*byte 1   : Inverse Version
*byte 2-3 : Type
*byte 4-7 : Length
*/

// Hex values
byte[] VERSION = "01".getBytes();
byte[] INVERSE_VERSION = "FE".getBytes();
byte[] TYPE = "9000".getBytes();
byte[] LENGTH = "02".getBytes();

ByteBuffer buf = ByteBuffer.wrap(this.header);
    buf.order(ByteOrder.BIG_ENDIAN);
    buf.put(VERSION);
    buf.put(INVERS_VERSION);
    buf.put(TYPE);
    //buf.put(LENGTH); <-- Overflow

//out
System.out.println(new String(buf.array(), "ASCII"));

Actual Output

01FE9000

Output Expected

01FE900020000000