This is an implementation of RFC 6902 JSON Patch written in Java.

Description & Use-Cases

• Java Library to find / apply JSON Patches according to RFC 6902.
• JSON Patch defines a JSON document structure for representing changes to a JSON document.
• It can be used to avoid sending a whole document when only a part has changed, thus reducing network bandwidth requirements if data (in JSON format) is required to send across multiple systems over network or in case of multi DC transfer.
• When used in combination with the HTTP PATCH method as per RFC 5789 HTTP PATCH, it will do partial updates for HTTP APIs in a standard way.

Compatible with : Java 7+ versions

Code Coverage

Package	Class, %	Method, %	Line, %
all classes	100% (6/ 6)	93.6% (44/ 47)	96.2% (332/ 345)

Complexity

• To find JsonPatch : Ω(N+M) ,N and M represents number of keys in first and second json respectively / O(summation of la*lb) where la , lb represents JSON array of length la / lb of against same key in first and second JSON ,since LCS is used to find difference between 2 JSON arrays there of order of quadratic.
• To Optimize Diffs ( compact move and remove into Move ) : Ω(D) / O(D*D) where D represents number of diffs obtained before compaction into Move operation.
• To Apply Diff : O(D) where D represents number of diffs

How to use:

Current Version : 0.4.16

Add following to <dependencies/> section of your pom.xml -

<groupId>com.flipkart.zjsonpatch</groupId>
<artifactId>zjsonpatch</artifactId>
<version>{version}</version>

• Available on maven central repository

API Usage

Obtaining JSON Diff as patch

JsonNode patch = JsonDiff.asJson(JsonNode source, JsonNode target)

Computes and returns a JSON patch from source to target, Both source and target must be either valid JSON objects or arrays or values. Further, if resultant patch is applied to source, it will yield target.

The algorithm which computes this JsonPatch currently generates following operations as per RFC 6902 -

• add
• remove
• replace
• move
• copy

Apply Json Patch

JsonNode target = JsonPatch.apply(JsonNode patch, JsonNode source);

Given a patch, it apply it to source JSON and return a target JSON which can be ( JSON object or array or value ). This operation performed on a clone of source JSON ( thus, the source JSON is unmodified and can be used further).

To turn off MOVE & COPY Operations

EnumSet<DiffFlags> flags = DiffFlags.dontNormalizeOpIntoMoveAndCopy().clone()
JsonNode patch = JsonDiff.asJson(JsonNode source, JsonNode target, flags)

Example

First Json

{"a": 0,"b": [1,2]}

Second json ( the json to obtain )

 {"b": [1,2,0]}

Following patch will be returned:

[{"op":"move","from":"/a","path":"/b/2"}]

here "op" specifies the operation ("move"), "from" specifies the path from where the value should be moved, and "path" specifies where value should be moved. The value that is moved is taken as the content at the "from" path.

Apply Json Patch In-Place

JsonPatch.applyInPlace(JsonNode patch, JsonNode source);

Given a patch, it will apply it to the source JSON mutating the instance, opposed to JsonPatch.apply which returns a new instance with the patch applied, leaving the source unchanged.

This is an extension to the RFC, and has some additional limitations. Specifically, the source document cannot be fully change in place (the Jackson APIs do not support that level of mutability). This means the following operations are not supported:

• remove with an empty or root path;
• replace with an empty or root path;
• move, add or copy targeting an empty or root path.

Tests:

1. 100+ selective hardcoded different input JSONs , with their driver test classes present under /test directory.
2. Apart from selective input, a deterministic random JSON generator is present under ( TestDataGenerator.java ), and its driver test class method is JsonDiffTest.testGeneratedJsonDiff().

*** Tests can only show presence of bugs and not their absence ***