没有使用android从服务器获取值到我的Textview中

import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

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

public class MainActivity extends AppCompatActivity {

    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = findViewById(R.id.textView);

        // 执行网络请求
        new FetchDataFromServerTask().execute();
    }

    private class FetchDataFromServerTask extends AsyncTask<Void, Void, String> {

        @Override
        protected String doInBackground(Void... voids) {
            String serverUrl = "http://example.com/data"; // 替换为实际的服务器URL

            try {
                URL url = new URL(serverUrl);
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.setRequestMethod("GET");

                // 发送请求并获取响应
                int responseCode = connection.getResponseCode();
                if (responseCode == HttpURLConnection.HTTP_OK) {
                    InputStream inputStream = connection.getInputStream();
                    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
                    StringBuilder response = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null) {
                        response.append(line);
                    }
                    reader.close();
                    inputStream.close();

                    return response.toString();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }

            return null;
        }

        @Override
        protected void onPostExecute(String result) {
            if (result != null) {
                // 将获取的值设置到TextView中
                textView.setText(result);
            }
        }
    }
}