This adds the ability to fully customize the JSON implementation used by a Flask application. Using a different JSON implementation can greatly speed up API applications that need to work with JSON in most requests.

app.json is an instance ofFlask.json_provider_class.flask.json.provider.JSONProvider is the base class that definesdumps,dump,loads,load, andresponse methods, of which onlydumps andloads need to be implemented. For example, here's a provider fororjson:

fromflask.json.providerimportJSONProviderimportorjsonclassOrJSONProvider(JSONProvider):defdumps(self,obj,*,option=None,**kwargs):ifoptionisNone:option=orjson.OPT_APPEND_NEWLINE|orjson.OPT_NAIVE_UTCreturnorjson.dumps(obj,option=option).decode()defloads(self,s,**kwargs):returnorjson.loads(s)# assign to an app instanceapp.json=OrJSONProvider(app)# or assign in a subclassclassMyFlask(Flask):json_provider_class=OrJSONProviderapp=MyFlask(__name__)

The methods inflask.json call the methods onapp.json if an app context is active, or fall back to thejson library.jsonify callsapp.json.response. The|tojson filter usesapp.json.dumps.Request.json usesapp.json.loads andResponse.json usesapp.json.dumps; the test client uses these as well.

Customizingjson_encoder orjson_decoder on an app or blueprint, and theJSONEncoder andJSONDecoder classes, are deprecated. This was not an effective way to use other libraries. Customizing per blueprint was requested by an API extension that is no longer maintained and didn't appear to use the feature. It's not clear how it would work with the new provider interface and added overhead to every request. Instead, API frameworks should be using a dedicated object serialization library, then taking advantage of a fast JSON serializer at the application level.

TheDefaultJSONProvider is the existing implementation using the built-injson library. Theapp.config keysJSON_AS_ASCII,JSON_SORT_KEYS,JSONIFY_MIMETYPE, andJSONIFY_PRETTYPRINT_REGULAR are deprecated and have moved to attributes on the default provider. Other providers are not required to support these options.