How to Convert a Hex String to a Byte Array in Java?

How can I convert a hexadecimal string, such as "00A0BF", into a byte array in Java?

String hexString = "00A0BF";

Converting a hexadecimal string into a byte array in Java can be accomplished efficiently using a straightforward method. Unlike using BigInteger, which might introduce complexity, we can achieve this using a combination of string manipulation and byte array operations.

public static byte[] hexStringToByteArray(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                             + Character.digit(s.charAt(i+1), 16));
    }
    return data;
}

// Usage example:
String hexString = "00A0BF";
byte[] byteArray = hexStringToByteArray(hexString); // {0x00, 0xA0, 0xBF}

Causes

• Using BigInteger unnecessarily complicates the conversion process.
• Inadequate string manipulation when parsing hex values could lead to errors.

Solutions

• Define the hex string without leading spaces or invalid characters.
• Use a loop to process each pair of characters from the string into a byte array.

Mistake: Assuming the string length is always even.

Solution: Ensure the string length is checked and padded if necessary.

Mistake: Not handling possible exceptions during parsing.

Solution: Implement error handling for invalid hex characters.