如何在httpPost方法中使用另一个类

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpClientUtil {
    public static String httpPost(String url, String postData) throws IOException {
        URL requestUrl = new URL(url);
        HttpURLConnection connection = (HttpURLConnection) requestUrl.openConnection();
        connection.setRequestMethod("POST");
        
        // 设置请求头信息
        connection.setRequestProperty("Content-Type", "application/json");
        
        // 发送请求体数据
        connection.setDoOutput(true);
        OutputStream outputStream = connection.getOutputStream();
        outputStream.write(postData.getBytes());
        outputStream.flush();
        outputStream.close();
        
        int responseCode = connection.getResponseCode();
        if (responseCode == HttpURLConnection.HTTP_OK) {
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            StringBuilder response = new StringBuilder();
            String line;
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
            reader.close();
            return response.toString();
        } else {
            throw new IOException("HTTP POST request failed with response code: " + responseCode);
        }
    }
}

public class Main {
    public static void main(String[] args) {
        try {
            String url = "http://example.com/api";
            String postData = "{\"key\": \"value\"}";
            String response = HttpClientUtil.httpPost(url, postData);
            System.out.println("Response: " + response);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}