Java HttpClient改变内容类型？

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.charset.StandardCharsets;

public class Main {
    public static void main(String[] args) throws IOException {
        String url = "https://example.com/api";
        String json = "{\"key\": \"value\"}";

        URL obj = new URL(url);
        HttpURLConnection connection = (HttpURLConnection) obj.openConnection();

        connection.setRequestMethod("POST");
        connection.setRequestProperty("Content-Type", "application/json;charset=UTF-8");
        connection.setRequestProperty("Accept", "application/json");
        connection.setDoOutput(true);

        connection.getOutputStream().write(json.getBytes(StandardCharsets.UTF_8));
        int responseCode = connection.getResponseCode();

        if (responseCode == HttpURLConnection.HTTP_OK) {
            BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String inputLine;
            StringBuilder response = new StringBuilder();

            while ((inputLine = in.readLine()) != null) {
                response.append(inputLine);
            }
            in.close();

            System.out.println(response.toString());
        } else {
            System.out.println("Request failed. Response code: " + responseCode);
        }
    }
}