Java POST请求不发送变量

import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.charset.StandardCharsets;

public class PostRequestExample {
    public static void main(String[] args) {
        try {
            // 创建URL对象
            URL url = new URL("http://example.com/api");

            // 创建HttpURLConnection对象
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();

            // 设置请求方法为POST
            conn.setRequestMethod("POST");

            // 设置请求头部信息
            conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

            // 启用输出流
            conn.setDoOutput(true);

            // 创建请求参数
            String params = "variable1=value1&variable2=value2";

            // 获取输出流并写入请求参数
            OutputStream os = conn.getOutputStream();
            byte[] postData = params.getBytes(StandardCharsets.UTF_8);
            os.write(postData);

            // 发送请求并获取响应
            int responseCode = conn.getResponseCode();
            System.out.println("Response Code: " + responseCode);

            // 关闭连接
            conn.disconnect();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}