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I have this json file that have a map of key-value pairs, but each value is a list of values

{
     "car":["BMW", "AUDI"],
      "OS":["Mac", "Win", "Ubuntu"],
      "food":["Burger", "Taco"]
}

I need to read them in a java class and convert this into an ordered hash. I know sets and hashes meant to be unordered, so if there is a way to get an ordered list of the keys only that would be very helpful. Also, if there is a way to reorder the info and get a list of keys that would be good too.

MSOUFAN
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  • You may want to clear up what you're asking. A "set of key/value pairs" is a map, and I'm guessing that's also what you mean by "hash". – SeverityOne Apr 23 '18 at 21:51
  • Yes, simply what I am asking is a way to read this file in that specific order. Car->OS->food – MSOUFAN Apr 23 '18 at 21:53
  • Maybe you misinterpreted my comment, but it's not clear what you're asking because you're using confusing terms. Also, on StackOverflow, you're expected to come up with an effort of what you've done so far, and which (presumably) isn't working. – SeverityOne Apr 23 '18 at 21:54
  • What is not working here is that there is no way in JAVA to read this JSON and write it on a console(for instance) in this specific order. – MSOUFAN Apr 23 '18 at 21:58
  • Create a `Model/Object` `String item; List subItems;` Then you can sort your `List` how you like. – SedJ601 Apr 23 '18 at 22:01
  • Please explain in detail why you need this in order. – chrylis -cautiouslyoptimistic- Apr 23 '18 at 22:28
  • Do you also care about the order of what is in the arrays as well? – Vinny Apr 24 '18 at 16:13

1 Answers1

2

I think what you meant was a Map, not a Set. A set does not have a key whereas a Map does.

  • HashMap is implemented as a hash table, and there is no ordering on keys or values.
  • TreeMap is implemented based on red-black tree structure, and it is ordered by the key.
  • LinkedHashMap preserves the insertion order
  • Hashtable is synchronized, in contrast to HashMap.

So in your case, if you want to preserve the insertion order, you should use LinkedHashMap. If you want to order it by the key, you should use TreeMap.

source

Update

To read it, you can use Gson:

String json = "{'car':['BMW', 'AUDI'],'OS':['Mac', 'Win', 'Ubuntu'],'food':['Burger', 'Taco']}";

// Convert the JSON String in a LinkedHashMap (to keep the insertion order)
Map<String, List<String>> map = new Gson().fromJson(json, new TypeToken<LinkedHashMap<String, List<String>>>(){}.getType());

// Print it, for proof
map.forEach((k, v) -> System.out.println("k = " + k + " | v = " + v));
TwiN
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