JSON custumize toString

Question

You can answer the entire question with only reading my question in BOLD letters below, I wanted to provide some context just in case the question is not clear

I am recreating a blockchain and therefore need to verify that the blocks created fullfill a given requirement (hashing the entire block (where the miner put in his nonce solution) has to be smaller than a given target).

So what I am currently doing and what is working is:

private static boolean checkDifficulty(JSONObject message) {
try {
        String blockString = message.get("block").toString();
        JSONObject blockPayLoad = (JSONObject) JSONValue.parse(blockString);
        BlockPayload block = new BlockPayload(blockPayLoad);
        BigInteger base = new BigInteger("2",16);
        String difficulty = Integer.toHexString(20+block.getDifficulty());
        BigInteger exponent = new BigInteger(difficulty,16);
        BigInteger totalSpace = base.pow(512);
        BigInteger target = totalSpace.divide(base.pow(exponent.intValueExact()));
        BigInteger hashedBlock3 = new BigInteger(1,hashSHA512(blockString));
return(hashedBlock3.compareTo(target) == -1);

    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
    }

    return false;

What I first thought I could do though, that I use my datastrucutre BlockPayload. The relevant part looks like this:

public BlockPayload(JSONObject blockPayLoad) {
    this.stringRepresentation = blockPayLoad.toString();
    this.type = blockPayLoad.get("type").toString();        
    this.transactions = blockPayLoad.get("transactions").toString();        
    this.timestamp = blockPayLoad.get("timestamp").toString();
    this.reward = blockPayLoad.get("reward").toString();
    this.difficulty = Integer.parseInt(blockPayLoad.get("difficulty").toString());
    this.nonce = blockPayLoad.get("nonce").toString();
    this.parent = blockPayLoad.get("parent").toString();
}

my toString() returns the stringReprensentation. Sadly, trying the same thing above (hashing the String reprensentation) yields a different result.

I figured that this is b/c my toString does not have the same order, meaning that the attributes' order within the JSONObject is changed.

So here is my question: Can I customize the toString() in a way, that i guarantee the attributes are shown in the wanted order?

Basil Battikhi · Accepted Answer · 2017-11-19T08:07:34.220

0

Yep you can put them in a treemap then you can hash them,tree map is a completely ordered map without do anything it is ordering the elements by keys from the lower to the higher take a look at https://beginnersbook.com/2013/12/treemap-in-java-with-example/

TreeMap<String, String> tmap = 
         new TreeMap<String, String>();
 tmap.put("1", "Data1");
  tmap.put("23", "Data2");
  tmap.put("70", "Data3");
  tmap.put("4", "Data4");
  tmap.put("2", "Data5");
// this will be like this after converting it to Json using Gson lib
// new Gson ().toJson(tmap);
{"1":"Data1","2":"Data5","23":"data2","4":"data4","70":"Data3"}

edited Nov 19 '17 at 08:07

answered Nov 19 '17 at 07:52

Basil Battikhi

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It has to stay within Json Format tho – InDaPond Nov 19 '17 at 07:59
so you want to order json ? – Basil Battikhi Nov 19 '17 at 08:00
there is a lib called Gson it converts from treemap to json structure then you can hash it – Basil Battikhi Nov 19 '17 at 08:01
Well actually I do not want to format it at all, but for some reason the String representation I get by saving the json.toString() call on that object is not the same as when I directly call the toString() which makes no sense to me, but nevertheless i want to make it look the same as the original one – InDaPond Nov 19 '17 at 08:55
if do you need the json order which you received, then the hashing will be always different you should order it alphabetically in order to get the right hash otherwise you have to make too many codes because if one attribute missed its order then you wil get the wrong hash – Basil Battikhi Nov 19 '17 at 09:00
Since you put in that much effort, and you provided the right question, I am upvoting and closing this topic. Nevertheless, It is not quite what I wanted, but that is because I asked the question in a wrong way. You find the new question here: https://stackoverflow.com/questions/47404356/how-to-prevent-json-from-removing-spaces – InDaPond Nov 21 '17 at 02:45

JSON custumize toString

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