android 使用 java 编写网络连通性检查

import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import java.net.HttpURLConnection;
import java.net.URL;

public final class NetCheck {

 public interface Callback {
void onResult(boolean ok);
 }

  /** 对外入口：主线程调用，回调仍在主线程 */
public static void isOnline(Context ctx, Callback cb) {
  if (!isConnected(ctx)) {
  cb.onResult(false);
  return;
 }
// 真正发 HTTP 探活
  new PingTask(cb).execute();
}

 /* ========== 内部实现 ========== */

  /* 1. 系统是否声明已连接 */
private static boolean isConnected(Context ctx) {
  ConnectivityManager cm = (ConnectivityManager)
ctx.getSystemService(Context.CONNECTIVITY_SERVICE);
  NetworkInfo info = cm.getActiveNetworkInfo();
 return info != null && info.isConnected();
  }

/* 2. 异步探活，避免 ANR */
 private static class PingTask extends AsyncTask<Void, Void, Boolean> {
private final Callback cb;
  PingTask(Callback cb) { this.cb = cb; }

 @Override
protected Boolean doInBackground(Void... voids) {
HttpURLConnection conn = null;
try {
 // ① 国内通用、响应快；② 支持 HEAD，省流量
  conn = (HttpURLConnection) new URL("https://www.baidu.com").openConnection();
conn.setRequestMethod("HEAD");
 conn.setConnectTimeout(3_000);
  conn.setReadTimeout(3_000);
int code = conn.getResponseCode();
 return (code >= 200 && code < 400);
 } catch (Exception e) {
  e.printStackTrace();
return false;
} finally {
 if (conn != null) conn.disconnect();
 }
}

  @Override
 protected void onPostExecute(Boolean ok) {
 cb.onResult(ok);
}
 }

  private NetCheck() {}
  }undefined✅ 使用示例（Activity/Fragment 内）NetCheck.isOnline(this, ok -> {
if (ok) {
// 真正连网
} else {
Toast.makeText(this, "网络不可用", Toast.LENGTH_SHORT).show();
}
});

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.INTERNET"/>