Canonicalizing JSON files

Python's JSON module is very usable from other programs:

generate_json | python -mjson.tool > canonical.json

If you're willing to go through a bit of overhead by calling

gson.toJson(canonicalize(gson.toJsonTree(obj)));

Then you can do something like this:

protected static JsonElement canonicalize(JsonElement src) {  if (src instanceof JsonArray) {    // Canonicalize each element of the array    JsonArray srcArray = (JsonArray)src;    JsonArray result = new JsonArray();    for (int i = 0; i < srcArray.size(); i++) {      result.add(canonicalize(srcArray.get(i)));    }    return result;  } else if (src instanceof JsonObject) {    // Sort the attributes by name, and the canonicalize each element of the object    JsonObject srcObject = (JsonObject)src;    JsonObject result = new JsonObject();    TreeSet<String> attributes = new TreeSet<>();    for (Map.Entry<String, JsonElement> entry : srcObject.entrySet()) {      attributes.add(entry.getKey());    }    for (String attribute : attributes) {      result.add(attribute, canonicalize(srcObject.get(attribute)));    }    return result;  } else {    return src;  }}

This is supported in Jackson:

@JsonPropertyOrder(alphabetic=true)

http://fasterxml.github.io/jackson-annotations/javadoc/2.3.0/com/fasterxml/jackson/annotation/JsonPropertyOrder.html