Question

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Convert a string representation of a hex dump to a byte array using Java?

For example, I have a string “DEADBEEF”. How can I convert it to byte[] bytes = { 0xDE, 0xAD, 0xBE, 0xEF } ?

Answer 1

Loop through each pair of two characters and convert each pair individually:

byte[] bytes = new byte[str.length()/2];

for( int i = 0; i < str.length(); i+=2 )
    bytes[i/2] = ((byte)Character.digit(str.charAt(i),16))<<4)+(byte)Character.digit(str.charAt(i),16);

I haven’t tested this code out (I don’t have a compiler with me atm) but I hope I got the idea through. The subtraction/addition simply converts ‘A’ into the number 10, ‘B’ into 11, etc. The bitshifting <<4 moves the first hex digit to the correct place.

EDIT: After rethinking it a bit, I’m not sure if you’re asking the correct question. Do you want to convert “DE” into {0xDE}, or perhaps into {0x44,0x45} ? The latter is more useful, the former is more like a homework problem type question.