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How get just one value from json as string

I have following json as string:
{
"field1":"value1",
"field2":"value2",
"field3":{
"field31":"value31",
"field32":"value32"
},
"field4":{
"field41":"value41"
}
}
What is the best and the most modern way to get from this json just value from field41, so I would return "value41". I know that I can use JSONObject but I'm wondering weather we have any other better option?

Try JSONPath
String json = "...";
String field41 = JsonPath.read(json, "$.field4.field41");
You can test it here - https://jsonpath.herokuapp.com/

If you want to generate a real object out of it you can use Gson. You need to describe the class first. There are online json to Java objects converters out there. And then you can just call:
YourObject obj = new Gson().fromJson(json,YourObject.class);
System.out.println(obj.getField4().getField41());
And there you have it!

Deserialize OneOf in two differents classes Java 11

My question is the following, I can receive a JSON, where inside it can come two types of class "CHANGE" or "WITHDRAW" in the same type of request. Below is an example JSON 1 and JSON 2
JSON 1
{
"name":"Eduard Jack",
"change":{
"agency":"3213"
}
}
JSON 2
{
"name":"john Stev",
"withdraw":{
"documentNumber":"121212"
}
}
When I make this request I get a string from json where I make a mapper to convert into an object, in the OPENAPI documentation it tells me that it is oneOf, it can be one or the other, never both together. How can I make the code understand which class to deserialize into in the Java 11?

I think there are multiple ways to do so
This will convert you string into JsonNode where JSON1 is the string provided
JsonNode json = mapper.readTree(JSON1);
if (json.get("withdraw") == null) : //the value of withdraw will be null in JSON1
JsonParser parser = mapper.treeAsTokens(json);
Change change= mapper.readValue(parser, Change.class);
else: //the value of withdraw wont be null in
JsonParser parser = mapper.treeAsTokens(json);
Withdraw withdraw= mapper.readValue(parser, withdraw.class);

How to map values of a json object without knowing about the format?

I have the following programming requirement:
problem:
Given two JSONs A and B, if the fields x,y,z in JSON A match the fields i,o,p in B return true else false.
approach:
I want to stay away from building a matching engine that depends on the json's format. I don't want to format the jsons by using pojos and then do object matching. My approach is to convert all the jsons into a hash map and then specify the location of the fields by using a string:
Example:
money -> a,b,c
{
a :
{
b : {
c: {
money : "100"
}
}
}
}
However this approach seems to be a bit tricky as we have to take into account collections. I have to cover all of the edge cases. Is there any spring library or java tool I can use to fulfill this purpose?.

There are many libraries being used for this purpose.The most popular one is com.google.gson
Usage:
JsonObject jo = (JsonObject)(jsonParser.parse("{somejsonstring}");<br>
jo.has("objectProperty") //Check if property exists
jo.get("objectProperty") // returns JsonElement,
jo.get("objectProperty").isJsonArray() // check if the property is the type that want
jo.getAsJsonArray("objectProperty") get the property

You may simplify this work by using im.wilk.vor:Voritem library gitHub or in Maven repository.
JsonElement je_one = jsonParser.parse("{some_json_string"})
JsonElement je_two = jsonParser.parse("{other_json_string"})
VorItem vi_one = vorItemFactory.from(je_one);
VorItem vi_two = vorItemFactory.from(je_two);
if (vi_one.get("a.b.c").optionalLong().isPresent() ) {
return vi_one.get("a.b.c").optionalLong().equals(vi_one.get("i.o.p").optionalLong())
}
return false;

Java/Android JSONArray inside JSONObject returning null

I'm developing an app for android that communicates with a server and receives JSON responses from it. Recently I changed the responses structure to contain more information about the requests.
Initially my responses where just the response from a mysqli_query encoded to JSON by the php function json_encode, and looked like this:
[
{"id":"31","description":"Hello"},
{"id":"32","description":"World"},
]
And to retrieve the objects, I would just create a new JSONArray object by calling my_json_array=new JSONArray(response) and iterate over it.
But now, my new responses contain extra data, like this:
{
"error":false,
"idCode":0,
"message":[
{
"id":"32",
"description":"Hello"
},
{
"id":"31",
"description":"World"
}
]
}
So now, as far as I understand, I need to convert this response to a JSONObject, and then extract the message as a JSONarray object by calling my_json_object.getJSONArray("message");.
I can extract the data from the "error" and the "idCode" fields normally, but when I try to extract the JSONArray from "message" it returns null, and no exceptions are thrown except for the NullPointerException.
I've validated the JSON string here, escaped the characters that could be problematic for java like the double quotes, removed uppercases, written the response as a single line, removed the double quotes surrounding the "id" value, used single quotes instead of double quotes, used harcoded string instead of the response from the server, checked the unicode representation of the string to see if contains any invalid characters (and it looks like it doesn't) and I don't know what else to do. Something to notice: the method toString() on the object returns the string "null", and based on the toString() method of the JSONObjects, it seems like the problem comes from the JSONStringer library, and going deeper on the classes it looks like the exception that there is a nesting problem, but I can't find any problem in my JSON string.
The important part of the code:
public String getResponse(){
web_helper.sendRequest();
//everything fine over here
return web_helper.getResponse();
}
public void printData(){ throws JSONExpection
JSONObject my_json_object=new JSONObject(getResponse());
System.out.println("error: "+my_json_object.getBoolean("error"));
System.out.println("idCode: "+my_json_object.getInt("idCode"));
JSONArray my_json_array=my_json_object.getJSONArray("message");
//not sure if the next part works because my_json_array is null
for(int i=0; i<my_json_array.length(); i++){
JSONObject obj=my_json_array.getJSONObject(i);
System.out.println("id: "+obj.getInt("id"));
System.out.println("description: "+obj.getString("description"));
}
}
Any help is appreciated, thank you in advance!.

How to handle unknown-type json response in java

I'm new to JSON.
I need to receive a response (in form of a String) from a server. That response can be an object like
{"a" : "value", "b" : "value2", ...}
if the request was successful, or a single string like
"ERROR"
on error.
Using org.json.JSONObject, how do I check which one has been returned?
EDIT
I think this could work, but I'm not sure if this is the right way to do it
if(JSONString.equals("\"ERROR\"") {
//handle error
} else {
//parse actual object
}
Where JSONString is a String containing the server response
Could this work?

The string "ERROR" is not valid JSON. Look at the JSONWriter API and you will see there is no way to produce a JSON string like "ERROR".
If you always want to treat the server response as json, you will need to have it return something like { "error" : true } or { error : false }. Your program will then be able to deserialize check the error field.
If you don't have control on the server response, then you will need to test String.equals("ERROR") before deserializing.

Since you can't make the third party service output valid json, before you do json parsing, just do a string comparison to see if the response is "error".

A quoted string is a valid json value in my opinion. The grammar at json.org does not define object or array as special topleve productions, rfc 4627 defines json-text as being an object or array, but a json value can also be a number, string, boolean or null.
From my reading of the org.json javadoc the following should work:
Object value = new JSONTokener(inputString).nextValue();
if (value instanceof String && ((String)value).equals("ERROR")) {
// handle error
} else if (value instanceof JSONObject) {
// handle response data
}
Using the tokener you are not affected by eventual additional whitespace in the response.