In Java, how do I convert a hex string to a byte[]? [duplicate]

Question

I am using the below function in Java to convert an encrypted String into hex format:

public static String toHex(byte [] buf) {     StringBuffer strbuf = new StringBuffer(buf.length * 2);     int i;     for (i = 0; i < buf.length; i++) {         if (((int) buf[i] & 0xff) < 0x10) {             strbuf.append("0");         }         strbuf.append(Long.toString((int) buf[i] & 0xff, 16));     }     return strbuf.toString(); } 

Now I want to convert that hex string back into a byte array. How can I do that?

For example,

(1) Plain Text = 123 (2) Encrypted Text = «h>kq*«¬Mí“~èåZ  \}? (3) Encrypted Text in Hex = f263575e7b00a977a8e9a37e08b9c215feb9bfb2f992b2b8f11e 

I can go from (2) to (3), but how do I go from (3) back to (2)?

Answer 1

The accepted answer does not consider leading zeros which may cause problems

This question answers it. Depending on whether you want to see how its done or just use a java built-in method. Here are the solutions copied from this and this answers respectively from the SO question mentioned.

Option 1: Util method

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; } 

Option 2: One-liner build-in

import javax.xml.bind.DatatypeConverter;  public static String toHexString(byte[] array) {     return DatatypeConverter.printHexBinary(array); }  public static byte[] toByteArray(String s) {     return DatatypeConverter.parseHexBinary(s); } 

Answer 2

 String s="f263575e7b00a977a8e9a37e08b9c215feb9bfb2f992b2b8f11e";  byte[] b = new BigInteger(s,16).toByteArray();