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Get available attributes (possibly recursive) from JSON Schema in Java

Let's say I've got the following JSON Schema:
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$id": "https://example.com/product.schema.json",
"title": "Draft JSON Schema",
"type": "object",
"properties": {
"person": {
"type": "object",
"properties": {
"details": {
"type": "object",
"properties": {
"first_name": {
"type": "string"
},
"last_name": {
"type": "string"
},
"groups": {
"type": "array",
"items": { "$ref": "#/$defs/existing_groups"
}
}
}
}
},
"$defs": {
"existing_groups": [ "Teachers", "Students" ]
},
"book": {
"type": "object",
"properties": {
"title": {
"type": "string"
},
"author": {
"type": "string"
}
}
}
}
}
From this schema, I would like to retrieve the available attributes and values at a defined depth:
So what's given is e.g. person.details and I want first_name, last_name, groups to be returned.
If person.details.groups is given, the possible values Student, Teacher should be returned.
If book.title is given, an empty Array or Set should be returned.
Apparently you can get attribute values from JSON objects with JsonPath, but I rather want to get possible attributes (and their possible values, if any are given) from a com.networknt.schema.JsonSchema.
What is the easiest way to do this in Java?

JSON Schema is for validating data. It has nothing to do with data manipulation or extraction. It's not comparable to JSONPath in any way.

Check for null in JSON schema

Is it possible to validate null in a schema like [is property A is null then there will be some required field]
For example:
"$schema": "http://json-schema.org/draft-04/schema#",
"id": "college.json#",
"title": "student",
"description": "syidentdetails",
"type": "object",
"properties": {
"colleges": {
"type": "array"
},
"school": {
"type": "array"
},
"if":{
"properties":{
"college":["type":null]
}
},"then":{["required":"school"]}
}

You need to define your type value in quotes as opposed to actual just null.
"type": "null"

Can declare your JSON Schema by a reference to type?

I am trying to validate a small bit of JSON like:
{
"success": true,
"message": "all's good!"
}
which works with the schema:
{
"type": "object",
"properties": {
"success": { "type": "boolean" },
"message": { "type": "string" }
}
}
however it fails with the schema
{
"definitions": {
"response": {
"type": "object",
"properties": {
"success": { "type": "boolean" },
"message": { "type": "string" }
}
}
},
"type": { "$ref": "#/definitions/response" }
}
with the error
java.lang.AssertionError: schema resource:/json-schema/sample.schema.json was > invalid: fatal: invalid JSON Schema, cannot continue
Syntax errors:
[ {
"level" : "error",
"message" : "value has incorrect type (found object, expected one of [array, string])",
"domain" : "syntax",
"schema" : {
"loadingURI" : "resource:/json-schema/sample.schema.json#",
"pointer" : ""
},
"keyword" : "type",
"found" : "object",
"expected" : [ "array", "string" ]
} ]
level: "fatal"
are you not allowed to use a reference for a type outside the definitions section? My motivation is that this is a response to a singular case, but there are cases where this structure is nested in others as well.
If it matters I'm using json-schema-validator version 2.2.6.
PS - this is a simplified example, the actual schema is more complicated as to justify why reuse and not copying and pasting is desirable.

You can use "id" and "$ref".
id for identifying, e.g.:
{
"type": "object",
"id": "#response",
"properties": {
"success": { "type": "boolean" },
"message": { "type": "string" }
}
}
}
And then you use $ref, e.g.:
"some": { "$ref": "#response" }
or external ref:
"ext": { "$ref": "http://url.com#response" }
See
http://json-schema.org/latest/json-schema-core.html#anchor27

The value of the type keyword must be a string of the name of one of the JSON primitave types (e.g. "string", "array", etc.), or an array of these strings. That is what the error message is saying. Keyword type must be a string or an array. The closest thing to what I think you are trying to do is this ...
{
"definitions": {
"response": {
"type": "object",
"properties": {
"success": { "type": "boolean" },
"message": { "type": "string" }
}
}
},
"allOf": [{ "$ref": "#/definitions/response" }]
}

You should declare your definition in it's own file, and they have your types refer to that file reference. See How to manage multiple JSON schema files? for details.

generating POJOs from JSON Schema for non-object types

I am trying to generate POJOs from the JSON Schema of XMBC.
I do this with jsonschema2pojo.
However, nothing gets generated. It doesn't even bring me an error.
This is a reduced sample json schema I am trying to generate from:
{
"description": "JSON-RPC API of XBMC",
"id": "http://xbmc.org/jsonrpc/ServiceDescription.json",
"methods": {
"Addons.ExecuteAddon": {
"description": "Executes the given addon with the given parameters (if possible)",
"params": [
{
"name": "addonid",
"required": true,
"type": "string"
},
{
"default": "",
"name": "params",
"type": [
{
"additionalProperties": {
"default": "",
"type": "string"
},
"type": "object"
},
{
"items": {
"type": "string"
},
"type": "array"
},
{
"description": "URL path (must start with / or ?",
"type": "string"
}
]
},
{
"default": false,
"name": "wait",
"type": "boolean"
}
],
"returns": {
"type": "string"
},
"type": "method"
}
},
"notifications": {
"Application.OnVolumeChanged": {
"description": "The volume of the application has changed.",
"params": [
{
"name": "sender",
"required": true,
"type": "string"
},
{
"name": "data",
"properties": {
"muted": {
"required": true,
"type": "boolean"
},
"volume": {
"maximum": 100,
"minimum": 0,
"required": true,
"type": "integer"
}
},
"required": true,
"type": "object"
}
],
"returns": null,
"type": "notification"
}
},
"types": {
"Addon.Content": {
"default": "unknown",
"enums": [
"unknown",
"video",
"audio",
"image",
"executable"
],
"id": "Addon.Content",
"type": "string"
}
},
"version": "6.14.3"
}
I must admin that my knowledge of JSON is very terse, maybe it is just a simple fault of mine. But can anyone help me how I can generate Java objects from such a JSON Schema?

The JSON Schema doesn't support method. JSON schema defines json data structure, it would not be used to define your methods. Most important attribute in JSON schema is properties.
It's good to generate POJO data models from a JSON schema, but not business logic. You can learn the JSON schema from those examples.

Jackson Parser for recursively parsing unknown input structure

I'm trying to parse recursively json input structure in java like the format below and trying to rewrite the same structure in another json.
Meanwhile I need to validate each & every json key/values while parsing.
{"Verbs":[{
"aaaa":"30d", "type":"ed", "rel":1.0, "id":"80", "spoken":"en", "ct":"on", "sps":null
},{
"aaaa":"31", "type":"cc", "rel":3.0, "id":"10", "spoken":"en", "ct":"off", "sps":null
},{
"aaaa":"81", "type":"nn", "rel":3.0, "id":"60", "spoken":"en", "ct":"on", "sps":null
}]}
Please advice how I can use Jackson parser JsonToken enums for reading and writing unknown json content.

You can use JSON Schema to validate your inputs.
Find the documentation for the data format, but from what I can read here, the schema would be something like this:
{
"$schema": "http://json-schema.org/schema#",
"type": "object",
"required": [ "Verbs" ],
"properties": {
"Verbs": { "type": "array", "items": { "$ref": "#/definitions/verb" } }
},
"definitions": {
"verb": {
"type": "object",
"required": [ "aaaa", "type", "rel", "id", "spoken", "ct", "sps" ],
"additionalProperties": false,
"properties": {
"aaaa": { "type": "string" },
"type": { "type": "string" },
"rel": { "type": "number" },
"id": { "type": "string", "pattern": "^[0-9]+$" },
"spoken": { "type": "string" },
"ct": { "enum": [ "on", "off" ] },
"sps": { "enum": [ null ] }
}
}
}
}
As you use Jackson, you can use this library which can validate your data for you.
Transforming your JSON after that can be done by creating a new JsonNode, for instance.