Question

What’s the best way to compare two JSON strings in Java? I want to be able to print out only the difference in key/values pairs.

I’m using gson library to convert it to a map and do assert but it displays both JSONs:

Type type = new TypeToken<Map<String, String>>() {}.getType();
Gson gson = new Gson();
Map<String, String> mapExpected = gson.fromJson(expectedJson, type);
Map<String, String> mapResponse = gson.fromJson(jsonResponse, type);
Assert.assertEquals(mapExpected, mapResponse);

Is there a better way to do this?

Answer 1

It is tricky, but it can be done.

I would implement a Pair class that holds both String (key and value), with its corresponding equals() and hashcode();

Then put all elements from Map A as Pair in a Set (setA) and all elements from Map B in another Set (setB)

Then calculate

 Set<Pair> setA_B = setA.removeAll(setB);
 Set<Pair> setB_A = setB.removeAll(setA);
 Set<Pair> result = setA_B.addAll(setB_A);

In result there are only the elements that do not match. If all elements match (both original maps are equal) then result is empty.