Httpclient in java send a POST request

I want to make an API caller with all CRUD methods using java
I want to be able to get all the data with json then parse it and only get data with it's unique id

The thing that I can't figure out is how do I send data using an API. I get that I can use an id but what if I need to modify not one but 2 or more fields how do I do it then while Parsing a json?

So I have implemented the GET method but I can't think of how to implement the POST one

Here is the code from my methods class where I have all the methods

I'm using Jackson to parse json and Java's Httpclient

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonPOJOBuilder;

import java.io.IOException;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.time.Duration;
import java.util.Collections;
import java.util.List;
import java.util.Map;

public class methods extends link{

    private final ObjectMapper mapper = new ObjectMapper();
    private final String url = "https://jsonplaceholder.typicode.com/todos";


    public List<dataGettingBack> getAllMethod() throws IOException, InterruptedException {


        HttpClient httpClientGet = HttpClient.newBuilder().connectTimeout(Duration.ofSeconds(10)).build();
        HttpRequest httpGetReq = HttpRequest
                .newBuilder(URI.create(url))
                .header("Content-Type", "application/json")
                .GET()
                .build();

        HttpResponse<String> res = httpClientGet.send(httpGetReq, HttpResponse.BodyHandlers.ofString());
        return mapper.readValue(res.body(), new TypeReference<List<dataGettingBack>>(){});
    }

    public List<dataGettingBack> getOne(int id) throws IOException, InterruptedException, error {
        HttpClient httpGetOne = HttpClient.newBuilder().connectTimeout(Duration.ofSeconds(10)).build();
        HttpRequest httpOne = HttpRequest
                .newBuilder(URI.create(url + "/"+ id))
                .header("Content-Type","application/json")
                .GET()
                .build();

        HttpResponse<String> responce = httpGetOne.send(httpOne, HttpResponse.BodyHandlers.ofString());

        if (responce.statusCode() == 404) { throw new error("Not found "+ responce.statusCode()); }


        return Collections.singletonList(mapper.readValue(responce.body(), dataGettingBack.class));
    }

    public void putMethod(int id) throws IOException, InterruptedException, error
    {
        HttpClient httpClientPut = HttpClient.newBuilder().connectTimeout(Duration.ofSeconds(10)).build();
        HttpRequest httpPutReq = HttpRequest
                .newBuilder(URI.create(url+ "/" +id))
                .PUT(HttpRequest.BodyPublishers.ofString(url))
                .header("Content-Type", "application/json")
                .build();

        HttpResponse<String> response = httpClientPut.send(httpPutReq, HttpResponse.BodyHandlers.ofString());

        
    }

    public void postMethod() {

        HttpClient httpClientPost = HttpClient.newBuilder().connectTimeout(Duration.ofSeconds(10)).build();
        HttpRequest httpPostReq = HttpRequest
                .newBuilder(URI.create(url))
                //.POST()
                .header("Content-Type", "application/json")
                .build();


    }



    public void deleteMethod(int id)
    {

        HttpClient httpClientDelete = HttpClient.newBuilder().connectTimeout(Duration.ofSeconds(10)).build();
        HttpRequest httpDelReq = HttpRequest
                .newBuilder(URI.create(url))
                .DELETE()
                .header("Content-Type", "application/json")
                .build();


    }

}

Here is how I get my data back

public record dataGettingBack(Integer userId, Integer id, String title, boolean completed) {}

That's the output when I run it all

[dataGettingBack[userId=1, id=10, title=illo est ratione doloremque quia maiores aut, completed=true]]

I also have an error class

public class error extends Throwable
{ public error(String massege) { super(massege); } }

as well as link class

abstract class link
{
    public String url;
}

That's what I have in main

public static void main(String[] args) throws Exception, error
{
    methods methods  = new methods();

    List<dataGettingBack> getAll = methods.getAllMethod();
    List<dataGettingBack> one = methods.getOne(10);

    System.out.println(one);
}

I started my programming classes a few months ago and that's my first project on my own

I used gson library to convert the data to json when sending it

public String putMethod(int id) throws IOException, InterruptedException, error
{
    HttpClient httpClientPut = HttpClient.newBuilder().connectTimeout(Duration.ofSeconds(10)).build();
    HttpRequest httpPutReq = HttpRequest
            .newBuilder(URI.create(url+ "/" +id))
            .PUT(HttpRequest.BodyPublishers.ofString(""))
            .header("Content-Type", "application/json")
            .build();

    HttpResponse<String> response = httpClientPut.send(httpPutReq, HttpResponse.BodyHandlers.ofString());
    dataGettingBack body = new dataGettingBack(3, 1,"test-test",true);

    return gson.toJson(body);
}