Question

这是我与日志一起使用的代码，由于我对使用数据库还很陌生，所以我不确定为什么会这样。我已经提供了登录验证和getConnection（）方法，因为我确定哪里出错了。感谢所有帮助。预先谢谢你。

public void validateLogin(){
        DatabaseConnection connectNow = new DatabaseConnection();
        Connection connectDB = connectNow.getConnection();

        String verifyLogin = "SELECT count(1) FROM user_account WHERE username = '" + usernameTextField.getText() + "' AND password ='" + passwordEnterField.getText() + "'";

        try{
            Statement statement = connectDB.createStatement();
            ResultSet queryResult = statement.executeQuery(verifyLogin);

            while (queryResult.next()){
                if (queryResult.getInt(1) == 1){
                    loginMessage.setText("Login Successful");
                }else {
                    loginMessage.setText("Invalid Login, try again");
                }
            }

        }catch (Exception e){
            e.printStackTrace();
            e.getCause();
        }
    }

getConnection（）方法：

public Connection getConnection(){
        String databaseName = "accounts";
        String databaseUser = "username";
        String databasePassword = "password";
        String url = "jdbc:mysql://localhost/" + databaseName;

        try{
            Class.forName("com.mysql.cj.jdbc.Driver");
            databaseLink = DriverManager.getConnection(url,databaseUser,databasePassword);
        }catch (Exception e){
            e.getStackTrace();
            e.getCause();
        }
        return databaseLink;
    }

日志： java.lang.NullPointerException：无法调用“ java.sql.Connection.createStatement（）”，因为“ connectDB”为空在Zimsy / demonic.LoginController.validateLogin（LoginController.java:67）在Zimsy / demonic.LoginController.loginButtonAction（LoginController.java:49）在java.base / jdk.internal.reflect.NativeMethodAccessorImpl.invoke0（本机方法）在java.base / jdk.internal.reflect.NativeMethodAccessorImpl.invoke（NativeMethodAccessorImpl.java:64）在java.base / jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke（DelegatingMethodAccessorImpl.java:43）在java.base / java.lang.reflect.Method.invoke（Method.java:564）在com.sun.javafx.reflect.Trampoline.invoke（MethodUtil.java:76）在jdk.internal.reflect.GeneratedMethodAccessor2.invoke（未知来源）在java.base / jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke（DelegatingMethodAccessorImpl.java:43）在java.base / java.lang.reflect.Method.invoke（Method.java:564）在javafx.base / com.sun.javafx.reflect.MethodUtil.invoke（MethodUtil.java:273）在javafx.fxml / com.sun.javafx.fxml.MethodHelper.invoke（MethodHelper.java:83）在javafx.fxml / javafx.fxml.FXMLLoader $ MethodHandler.invoke（FXMLLoader.java:1782）在javafx.fxml / javafx.fxml.FXMLLoader $ ControllerMethodEventHandler.handle（FXMLLoader.java:1670）在javafx.base / com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent（CompositeEventHandler.java:86）在javafx.base / com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent（EventHandlerManager.java:238）在javafx.base / com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent（EventHandlerManager.java:191）在javafx.base / com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent（CompositeEventDispatcher.java:59）在javafx.base / com.sun.javafx.event.BasicEventDispatcher.dispatchEvent（BasicEventDispatcher.java:58）在javafx.base / com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent（EventDispatchChainImpl.java:114）在javafx.base / com.sun.javafx.event.BasicEventDispatcher.dispatchEvent（BasicEventDispatcher.java:56）在javafx.base / com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent（EventDispatchChainImpl.java:114）在javafx.base / com.sun.javafx.event.BasicEventDispatcher.dispatchEvent（BasicEventDispatcher.java:56）在javafx.base / com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent（EventDispatchChainImpl.java:114）在javafx.base / com.sun.javafx.event.EventUtil.fireEventImpl（EventUtil.java:74）在javafx.base / com.sun.javafx.event.EventUtil.fireEvent（EventUtil.java:49）在javafx.base / javafx.event.Event.fireEvent（Event.java:198）在javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8879）在javafx.controls / javafx.scene.control.Button.fire（Button.java:200）在javafx.controls / com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased（ButtonBehavior.java:206）在javafx.controls / com.sun.javafx.scene.control.inputmap.InputMap.handle（InputMap.java:274）在javafx.base / com.sun.javafx.event.CompositeEventHandler $ NormalEventHandlerRecord.handleBubblingEvent（CompositeEventHandler.java:218）在javafx.base / com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent（CompositeEventHandler.java:80）在javafx.base / com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent（EventHandlerManager.java:238）在javafx.base / com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent（EventHandlerManager.java:191）在javafx.base / com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent（CompositeEventDispatcher.java:59）在javafx.base / com.sun.javafx.event.BasicEventDispatcher.dispatchEvent（BasicEventDispatcher.java:58）在javafx.base / com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent（EventDispatchChainImpl.java:114）在javafx.base / com.sun.javafx.event.BasicEventDispatcher.dispatchEvent（BasicEventDispatcher.java:56）在javafx.base / com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent（EventDispatchChainImpl.java:114）在javafx.base / com.sun.javafx.event.BasicEventDispatcher.dispatchEvent（BasicEventDispatcher.java:56）在javafx.base / com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent（EventDispatchChainImpl.java:114）在javafx.base / com.sun.javafx.event.EventUtil.fireEventImpl（EventUtil.java:74）在javafx.base / com.sun.javafx.event.EventUtil.fireEvent（EventUtil.java:54）在javafx.base / javafx.event.Event.fireEvent（Event.java:198）在javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3851）在javafx.graphics/javafx.scene.Scene$MouseHandler.access$1200(Scene.java:3579）在javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849）在javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2588）在javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:397）在javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295）在java.base / java.security.AccessController.doPrivileged（AccessController.java:391）在javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:434）在javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:390）在javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:433）在javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556）在javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942）在javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop（本机方法）在javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174）在java.base / java.lang.Thread.run（Thread.java:832）

获取无法调用“ java.sql.connect.createStatement（）”，因为“ connectDB”为空

0 个答案: