为什么不在设备上工作而在模拟器上工作？

Question

我正在制作一个访问mysql数据库的应用程序。我使用的是直接JDBC，而不是Web服务。模拟器访问没有问题，但实际设备给出了错误

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.

这是连接类的代码（仅是连接方法）

public static Connection CONN(String name) {
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder()
            .permitAll().build();
    StrictMode.setThreadPolicy(policy);
    Connection conn = null;
    String ConnURL = null;
    try {

        Class.forName(classs);

        conn = DriverManager.getConnection(url, un, password);


        String stsql = "Select version()";


        Toaster.toast(name);


        //conn = DriverManager.getConnection(ConnURL);
    } catch (SQLException se) {
        Log.e("ERRO", se.getMessage());
        Toaster.toast(se.getMessage());
        System.out.println( se.getMessage() );
    } catch (ClassNotFoundException e) {
        Log.e("ERRO", e.getMessage());
    } catch (Exception e) {
        Log.e("ERRO", e.getMessage());
    }
    return conn;
}

有人可以给我一些帮助吗？ 谢谢！