空对象引用上的 Android Studio jTDS java.lang.NullPointerException java.sql.Statement java.sql.Connection.cr

Posted 2023-02-15

【中文标题】空对象引用上的 Android Studio jTDS java.lang.NullPointerException java.sql.Statement java.sql.Connection.createStatement()

【英文标题】：Android Studio jTDS java.lang.NullPointerException java.sql.Statement java.sql.Connection.createStatement() on a null object reference

【发布时间】：2021-12-24 03:21:43

【问题描述】：

我正在尝试创建一个连接到 Microsoft SQL Server 的应用程序，并将一些数据添加到一个表（供应商）中，但它一直拒绝我与服务器的连接。我只为这个数据库创建了一个用户和一个密码。我正在使用 MacBook，而服务器在另一台 Windows PC 上，但我认为这不是它无法正常工作的原因。对于ip，我使用了我在cmd中编写ipconfig时找到的IPv4。

这是代码：

public class connectClass 
    private Connection connection;

    public Connection connectClass()
        String ip = "won't put it here for obvious reasons";
        String user = "android";
        String password = "android";
        String port = "1433";
        String database = "dbExemplu";
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(policy);

        try
            Class.forName("net.sourceforge.jtds.jdbc.Driver");
            String sirUrl = "jdbc:jtds:sqlserver://" + ip + ":" + port + ";" + "databasename=" + database
                    + ";user=" + user + ";password=" + password + ";";
            connection = DriverManager.getConnection(sirUrl);
         catch (ClassNotFoundException e) 
            Log.e("Error", e.getException() + " " + e.getMessage());
         catch (SQLException e) 
            Log.e("Error", e.getMessage());
        
        return connection;
    


public class MainActivity extends AppCompatActivity 
    private Button btn1;
    private EditText txtCode, txtName, txtPhone;
    private Vendor vendor;
    private Collections cols = new Collections();
    private Connection connection;

@Override
    protected void onCreate(@Nullable Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        txtCode = findViewById(R.id.codeVendor);
        txtName = findViewById(R.id.nameVendor);
        txtPhone = findViewById(R.id.phoneVendor);

        btn1 = findViewById(R.id.saveVendor);

        connectClass connect = new connectClass();
        connection = connect.connectClass();

btn1.setOnClickListener(new View.OnClickListener() 
            @Override
            public void onClick(View view) 
                vendor = new Vendor();
                vendor(txtCode.getText().toString());
                vendor.setName(txtName.getText().toString());
                vendor.setPhone(txtPhone.getText().toString());
                cols.vendors.add(vendor);
                addVendor(vendor.getCode().toString(), vendor.getName().toString(), vendor.getPhone().toString);

);

        void addVendor(String code, String name, String phone) 
        Statement st;
        String s;
        try 
            st = connection.createStatement();
            s = "insert into Furnizori values ('" + code + "'" + ",'" + name + "','" + phone + "')";
            st.executeUpdate(s);

         catch (Exception e) 
            Log.e("Error", e.getMessage());
        
    

【参考方案1】：

我想通了。我的 SQL Server 身份验证设置为仅 Windows 身份验证，我必须将其设置为 SQL Server 身份验证。