在android应用程序和MS之间创建连接

Question

我的代码：

Button loginbtn;
    TextView errorlbl;
    EditText edname, edpassword;
    Connection connect;
    PreparedStatement preparedStatement;
    Statement st;
    String ipaddress, db, username, password;


    @SuppressLint("NewApi")
    private Connection ConnectionHelper(String user,String password,String database, String server)
    {
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(policy);
        Connection connection = null;
        String ConnectionURL = null;
        try {
            Class.forName("net.sourceforge.jtds.jdbc.Driver");
            ConnectionURL = "jdbc:jtds:sqlserver://" + server + ";database name =" + database + ";user =" + user + ";password =" + password + ";" ;
            connection = DriverManager.getConnection(ConnectionURL);
        }
        catch (SQLException se)
        {
            Log.e("Error", se.getMessage());
        }
        catch (ClassNotFoundException e)
        {
            Log.e("Error",e.getMessage());
        }
        catch (Exception e)
        {
            Log.e("Error",e.getMessage());
        }
        return connection;
    }

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

        loginbtn = (Button) findViewById(R.id.btn_login);
        errorlbl = (TextView) findViewById(R.id.lbl_error);
        edname = (EditText) findViewById(R.id.txt_username);
        edpassword = (EditText) findViewById(R.id.txt_password);

        ipaddress = "xxxxxxxxx";
        username = "xxxxxxx";
        password = "xxxxxxx";
        db = "DKMobile";

        connect = ConnectionHelper(username,password,db,ipaddress);
        loginbtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                try{
                    connect = ConnectionHelper(username, password, db, ipaddress);
                    st = connect.createStatement();
                    ResultSet rs = st.executeQuery("Select * from DKMUsers where user_ID = '"+ edname.getText().toString()+"'and Password = '"+edpassword.getText().toString()+"'");
                    if(rs!=null && rs.next()){
                        Intent i = new Intent(MainActivity.this,MainActivity.class);
                        startActivity(i);
                    }
                    else {
                        errorlbl.setText("Sorry, wrong credentials!!!");

                    }

                }catch (SQLException e)
                {
                    errorlbl.setText(e.getMessage().toString());
                }
            }
        });

逻辑猫：

>08-12 16:46:20.183    2027-2027/com.dk.dkmobile E/Error﹕ Single-Sign-On is only supported on Windows. Please specify a user name.
08-12 16:51:49.661    2027-2027/com.dk.dkmobile E/Error﹕ Single-Sign-On is only supported on Windows. Please specify a user name.
08-12 16:51:49.661    2027-2027/com.dk.dkmobile D/AndroidRuntime﹕ Shutting down VM
    --------- beginning of crash
08-12 16:51:49.669    2027-2027/com.dk.dkmobile E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.dk.dkmobile, PID: 2027
    java.lang.NullPointerException: Attempt to invoke interface method 'java.sql.Statement java.sql.Connection.createStatement()' on a null object reference
            at com.dk.dkmobile.MainActivity$1.onClick(MainActivity.java:83)
            at android.view.View.performClick(View.java:4780)
            at android.view.View$PerformClick.run(View.java:19866)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
08-12 16:51:54.120    2027-2027/com.dk.dkmobile I/Process﹕ Sending signal. PID: 2027 SIG: 9

当我将用户名和密码的值放在一起时，模拟器显示了消息：

不幸的是，您的应用程序已经停止工作。有人能指点我解决这个问题吗。提前感谢

Answer 1

这不是将移动应用程序与数据库连接的正确方法。相反，您应该创建一个在服务器上运行的中间件(REST/)。这个中间件将反过来连接数据库和您的移动应用程序，无论是安卓、iOS还是windows应用程序都可以与该中间件通信。

Answer 2

您正在尝试连接到mysql。您应该创建php/jsp或任何在线运行查询并以json或xml格式带来数据的语言，然后使用异步任务使用httpclient解析这些数据。这将是一个更好的方法

Answer 3

如果没有任何服务器通信(Web服务)，你就不能在安卓应用程序中使用网站数据库。

如果您想管理网站和android应用程序之间的通信，就意味着您需要一个拥有web/移动应用程序数据的集中式服务器。因此，通过使用web服务方法(休息/肥皂)，您可以实现它们之间的通信。