Java convert String of byte array to byte array

Question

I got a byte array sent from javascript by ajax looking like this:

"89,50,4e,47,0d,0a,1a,0a,00,00,00,0d,49,48,44,52,00,00,01,98,00,00,00,e4,08,06,00 ..."

I would like to convert this string to a byte array. Pretty similar to this question, but using Java instead: Convert String[] to byte[] array

Edit: This seems to work - but not sure if i am doing it right

    String[] byteData ="89,50,4e,47,0d,0a,1a,0a,00,00,00,0d,49,48,44,52,00,00,01,98,00,00,00,e4,08,06,00";
    byte[] b = new byte[byteData.length];
    for (int i = 0; i < byteData.length; i++) {
        BigInteger bla = BigInteger.valueOf(Integer.parseInt(byteData[i].trim(), 16) - 128);
        b[i] = bla.toByteArray()[0];
    }

You have String(byte[]), you just need to read the String to decode the bytes one by one to create that byte[], try and come back if you can't. — AxelH
– AxelH, Commented Jun 8, 2017 at 10:37
The general process would be to String::split at the commas, write a convert hexToDec() function, subtract 128 from result, then cast to byte. There is no such thing as a uByte in Java, that is why you would need to subtract 128 from result — CraigR8806
– CraigR8806, Commented Jun 8, 2017 at 10:38

Gleb Khrystenko · Accepted Answer · 2017-06-08 11:06:35Z

0

You can try this

String response ="89,50,47,00,00,00,49,48,44,52,00,00,01,98,00,00,00,08";

List<Byte> byteList = Arrays.stream(response.split(","))
   .map(Byte::parseByte)
   .collect(Collectors.toList());

same as previous but with stream xD

but your example throws NumberFormatException on 4e, 0d and so on

answered Jun 8, 2017 at 11:06

Gleb Khrystenko

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6 Comments

Jacob G. Over a year ago

OP wants a byte array, not a List<Byte>

sofarsoghood Over a year ago

eehm NumberFormatException xD

Gleb Khrystenko Over a year ago

@JacobG. you can use .toArray(Byte[]::new) instead of .collect(Collectors.toList())

Gleb Khrystenko Over a year ago

@sofarsoghood are you sure about dat string? Is it 100% valid?

Gleb Khrystenko Over a year ago

@sofarsoghood have you tried response.getBytes() ? it returns byte[] from string

|

Mohamed Ali RACHID · Accepted Answer · 2017-06-08 11:55:56Z

0

here is a simple solution with JAVA :

        String bytes="89,50,4e,47,0d,0a,1a,0a,00,00,00,0d,49,48,44,52,00,00,01,98,00,00,00,e4,08";
        String []tab=bytes.split(",");
        Integer []b = new Integer[tab.length];
        for(int i = 0 ; i < tab.length ; i++){
             if(tab[i].matches("[-+]?\\d*\\.?\\d+"))
                 b[i]=Integer.parseInt(tab[i]);
             else
                 b[i]=Integer.parseInt(tab[i],16);


        }

edited Jun 8, 2017 at 11:55

answered Jun 8, 2017 at 10:52

Mohamed Ali RACHID

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6 Comments

sofarsoghood Over a year ago

java.lang.NumberFormatException: For input string: "4e" at b[i]=Byte.parseByte(tab[i]);

Mohamed Ali RACHID Over a year ago

i edited the answer , this will solve the problem : b[i]=Byte.parseByte(tab[i],16);

tmucha Over a year ago

Unfortunatelly this cause problem: Exception in thread "main" java.lang.NumberFormatException: Value out of range. Value:"89" Radix:16

sofarsoghood Over a year ago

hmm java.lang.NumberFormatException: Value out of range. Value:"89" Radix:16 at b[i]=Byte.parseByte(tab[i],16); :/

Mohamed Ali RACHID Over a year ago

so we have to test if the string is numeric or not , if it's not u parse it as hex , try it now :)

if(tab[i].matches("[-+]?\\d*\\.?\\d+"))              b[i]=Byte.parseByte(tab[i]);          else              b[i]=Byte.parseByte(tab[i],16);

|

tmucha · Accepted Answer · 2017-06-08 12:27:45Z

0

Try below code (output is result of conversion):

    String input = "89,50,4e,47,0d,0a,1a,0a,00,00,00,0d,49,48,44,52,00,00,01,98,00,00,00,e4,08";

    String[] hex = input.split(",");
    char[] chars = new char[hex.length];
    for (int i = 0; i < hex.length; i++) {
        chars[i] = (char) Integer.parseInt(hex[i], 16);
    }
    String output = new String(chars);

answered Jun 8, 2017 at 12:27

tmucha

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Comments

Nyamiou The Galeanthrope · Accepted Answer · 2017-06-08 12:46:28Z

EDIT: Actually parseByte doesn't seems to be a safe choice for your case because of this, so I took inspiration from this answer to change it.

You can do:

String bytesAsStringWithCommas = "89,50,4e,47,0d,0a,1a,0a,00,00,00,0d,49,48,44,52,00,00,01,98,00,00,00,e4,08,06,00 ...";
String[] bytesStr = bytesAsStringWithCommas.split(",");
byte[] byteArray = new byte[bytesStr.length];
for (int j = 0; j < bytesStr.length; j++) {
    byteArray[j] = (byte) ((Character.digit(bytesStr[j].charAt(0), 16) << 4) + Character.digit(bytesStr[j].charAt(1), 16));
}

You should probably change your server code or client code to send data directly instead of using convoluted solutions like this one. Or you can also use Base64 encoding, which is going to be already better than your current solution.

You are perfectly right, thx. But I found that parseByte is not a very good choice actually (see edit).

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