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Along will all the previous work to the library by Travis on json-patch this library provides a little custom and more accurate difference in form of add, remove and replace only.

The Custom diff only compute difference in form of add, remove and replace. The add, remove and replace operation is same as specified in rfc6901 but only in case of object,there is change in case of array diff operations the remove and replace operations have attached extra {original_value: value} which helps us to keep track of the state before the difference was calculated.

In case of absence of Key the Algorithm treats whole object as Key and calculates fine-grained difference between the JsonNode.

This Library Supports Custom Operation in Case of Array as ...

provided the Map<JsonPointer, String> has {"/a": "b"}

Remove Operation

source     :  { "a": [ { "a": "b" }, { "a": "x", "b": "c" } ] }
target     :  { "a": [ { "a": "b" } ] }
Difference :  [ { "op": "remove", "path": "/a/1", "original_value": { "a": "x", "b": "c" } } ]

Replace Operation

source     : { "a": [ { "a": "b", "b": "a" } ] }
target     : { "a": [ { "a": "b", "b": "c" } ] }
Difference : [ { "op": "replace", "path": "/a/0/b", "value": "c", "original_value": { "a": "b", "b": "a" } } ] 

It is able to do even more than that. See the test files in the project.

The main class is JsonDiff. It returns the patch as a JsonPatch or as a JsonNode. Sample usage:

final JsonPatch patch = JsonDiff.asJsonPatch(source, target, attributeKeyFieldMap);
final JsonNode patchNode = JsonDiff.asJson(source, target, attributeKeyFieldMap);

attributeKeyFieldMap is the Map of <JsonPointer,String>, read RFC6902 for JsonPointer. JsonPointer contains all the Key Fields Inside an Array object which you want to treat as primary Key.

The API offers no guarantee at all about patch "reuse"; that is, the generated patch is only guaranteed to safely transform the given source to the given target. Do not expect it to give the result you expect on another source/target pair!