Getting a diff of two JSON strings using Java code

Question

Can anybody suggest some Java Library or Code to get a diff of two JSON Strings?

Answer 1

I had the exact same problem and ended up writing my own library:

https://github.com/algesten/jsondiff

It does both diffing/patching.

Diffs are JSON-objects themselves and have a simple syntax for object merge/replace and array insert/replace.

Example:

original
{
   a: { b: 42 }
}

patch
{
  "~a" { c: 43 }
}

The ~ indicates an object merge.

result
{
   a: { b: 42, c: 43 }
}

Answer 2

For one specific suggestion, you could use Jackson, bind JSON strings into JSON trees, and compare them for equality. Something like:

ObjectMapper mapper = new ObjectMapper();
JsonNode tree1 = mapper.readTree(jsonString1);
JsonNode tree2 = mapper.readTree(jsonString2);
if (tree1.equals(tree2)) { 
  // yes, contents are equal -- note, ordering of arrays matters, objects not
} else { 
  // not equal
}

equality comparison is by value and should work as expected with respect to JSON arrays, objects and primitive values.

Answer 3

Personally, I would suggest de-serializing the JSON strings back into objects and comparing the objects.

That way you don't have to worry about extra whitespace/formatting between the two JSON strings (two strings could be formatted wildly different and still represent equal objects).