如何解决基本POST请求的java.lang.IllegalStateException:已连接

import java.io.*;
import java.net.*;

public class PostRequestExample {
    public static void main(String[] args) {
        try {
            // 1. 创建URL对象
            URL url = new URL("http://example.com/api/post");

            // 2. 打开URL连接
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();

            // 3. 设置URLConnection属性
            connection.setRequestMethod("POST");
            connection.setConnectTimeout(5000);
            connection.setReadTimeout(5000);
            connection.setDoOutput(true);

            // 4. 获取输出流
            OutputStream outputStream = connection.getOutputStream();

            // 5. 写入POST参数
            BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(outputStream));
            writer.write("param1=value1&param2=value2");
            writer.flush();
            writer.close();

            // 6. 关闭输出流
            outputStream.close();

            // 7. 获取输入流
            InputStream inputStream = connection.getInputStream();

            // 8. 读取响应数据
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
            String line;
            StringBuilder response = new StringBuilder();
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
            reader.close();

            // 9. 关闭输入流和连接
            inputStream.close();
            connection.disconnect();

            // 输出响应数据
            System.out.println(response.toString());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}