为什么会出错？

Question

我在以下代码中遇到一个问题：

public Menu menu;
public TextView tv;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    TextView textv = (TextView)this.findViewById(R.id.mysql);
    tv = textv;
    Connect();

}

@Override
public boolean onCreateOptionsMenu(Menu menu)
{
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.menu, menu);
    return super.onCreateOptionsMenu(menu);
}

public boolean onOptionsItemSelected(MenuItem item){
    switch(item.getItemId()){
        case R.id.login:
            Intent loginIntent = new Intent(this, LoginActivity.class);
            startActivityForResult(loginIntent, LOGIN_REQUEST);
            return true;
        case R.id.register:

            return true;
        default:    
            return super.onOptionsItemSelected(item);
    }
}   
protected void onStop(){
    super.onStop();
}

protected void onDestroy(){
    super.onDestroy();
}


@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    if(requestCode == LOGIN_REQUEST){
        if(resultCode == RESULT_OK){

        }
    }
    super.onActivityResult(requestCode, resultCode, data);
}

    private class Connect extends AsyncTask<String, Void, String> {
        @Override
        protected String doInBackground(String... urls) {
            String response = "";

            try {
                Class.forName("com.mysql.jdbc.Driver");
                Connection con = DriverManager.getConnection(url, user, pass);
                System.out.println("Database connection success"); 

                String result = "Database connection success\n";
                Statement st = con.createStatement();
                ResultSet rs = st.executeQuery("select * from login");
                ResultSetMetaData rsmd = rs.getMetaData();

                while(rs.next()) {
                    result += rsmd.getColumnName(1) + ": " + rs.getInt(1) + "\n";
                    result += rsmd.getColumnName(2) + ": " + rs.getString(2) + "\n";
                    result += rsmd.getColumnName(3) + ": " + rs.getString(3) + "\n";
                }
                tv.setText(result);
            }
            catch(Exception e) {
                e.printStackTrace();
                tv.setText(e.toString());
            }
            return response;   


        }

        @Override
        protected void onPostExecute(String result) {
            tv.setText(result);
        }
    }

    public void Connect() {
        Connect task = new Connect();
        task.execute();

    }

在第80行，即行：

Connection con = DriverManager.getConnection(url, user, pass);

但我不知道为什么。 我不会忘记互联网许可 我认为连接器库有问题。