JavaFX学生注册应用出现NumberFormatException错误求助

点击Register按钮时触发异常，错误根源为NumberFormatException: For input string: ""，即空字符串无法转换为Integer类型。

错误信息 #

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml@19-ea/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1857)
    at javafx.fxml@19-ea/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1724)
    at javafx.base@19-ea/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at javafx.base@19-ea/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
    at javafx.base@19-ea/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base@19-ea/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base@19-ea/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base@19-ea/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@19-ea/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@19-ea/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@19-ea/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@19-ea/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@19-ea/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base@19-ea/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.base@19-ea/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics@19-ea/javafx.scene.Node.fireEvent(Node.java:8797)
    at javafx.controls@19-ea/javafx.scene.control.Button.fire(Button.java:203)
    at javafx.controls@19-ea/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:208)
    at javafx.controls@19-ea/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
    at javafx.base@19-ea/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
    at javafx.base@19-ea/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at javafx.base@19-ea/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
    at javafx.base@19-ea/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base@19-ea/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base@19-ea/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base@19-ea/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@19-ea/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@19-ea/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@19-ea/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base@19-ea/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base@19-ea/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base@19-ea/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.base@19-ea/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics@19-ea/javafx.scene.Scene$MouseHandler.process(Scene.java:3881)
    at javafx.graphics@19-ea/javafx.scene.Scene.processMouseEvent(Scene.java:1874)
    at javafx.graphics@19-ea/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2607)
    at javafx.graphics@19-ea/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:411)
    at javafx.graphics@19-ea/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:301)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
    at javafx.graphics@19-ea/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:450)
    at javafx.graphics@19-ea/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
    at javafx.graphics@19-ea/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
    at javafx.graphics@19-ea/com.sun.glass.ui.View.handleMouseEvent(View.java:551)
    at javafx.graphics@19-ea/com.sun.glass.ui.View.notifyMouse(View.java:937)
    at javafx.graphics@19-ea/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics@19-ea/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
    at java.base/java.lang.Thread.run(Thread.java:1589)
Caused by: java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:119)
    at java.base/java.lang.reflect.Method.invoke(Method.java:578)
    at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:77)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
    at java.base/java.lang.reflect.Method.invoke(Method.java:578)
    at javafx.base@19-ea/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml@19-ea/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:84)
    at javafx.fxml@19-ea/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1852)
    ... 46 more
Caused by: java.lang.NumberFormatException: For input string: ""
    at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
    at java.base/java.lang.Integer.parseInt(Integer.java:675)
    at java.base/java.lang.Integer.valueOf(Integer.java:992)
    at com.example.studentdatabase/com.example.studentdatabase.Register.register(Register.java:99)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
    ... 53 more

问题分析 #

从代码片段可以看到，错误出在register方法的执行顺序：先清空了所有输入文本框，再尝试读取空文本框的内容转换为Integer来拼接SQL语句，自然触发空字符串转Integer的异常。

原问题代码片段：

public void register(ActionEvent event){
    if(hasFirstName && hasLastName && hasAge && hasGrade){
        studentID++;
        warning.setText("Registration Completed!");
        warning.setVisible(true);
        // 此处清空文本框
        firstNameTF.setText("");
        lastNameTF.setText("");
        ageTF.setText("");
        GradeTF.setText("");
        // ...重置其他状态
        // 此处使用已清空的文本框内容转Integer
        String registerString = "INSERT INTO student_data(student_id,first_name,last_name,age,grade) VALUES('"+studentID+"','"+firstNameTF.getText()+"','"+lastNameTF.getText()+"','"+Integer.valueOf(ageTF.getText())+"','"+Integer.valueOf(GradeTF.getText())+"')";
        try{
            Statement statement = connection.createStatement();
            statement.executeUpdate(registerString);
        }catch(Exception e){
            e.printStackTrace();
            e.getCause();
        }
    }else{
        warning.setText("Fields are Empty!");
        warning.setVisible(true);
    }
}

解决方案 #

• 先获取输入框的内容并存储到变量中，确保使用的是用户输入的有效数据
• 使用PreparedStatement拼接SQL，避免SQL注入风险和字符串拼接错误
• 执行数据库操作成功后，再清空输入框和重置UI状态

修复后的代码：

public void register(ActionEvent event){
    if(hasFirstName && hasLastName && hasAge && hasGrade){
        studentID++;
        // 先获取用户输入的有效数据，trim()去除前后空格
        String firstName = firstNameTF.getText().trim();
        String lastName = lastNameTF.getText().trim();
        int age = Integer.valueOf(ageTF.getText().trim());
        int grade = Integer.valueOf(GradeTF.getText().trim());
        
        // 使用PreparedStatement防止SQL注入
        String registerString = "INSERT INTO student_data(student_id,first_name,last_name,age,grade) VALUES(?,?,?,?,?)";
        try{
            PreparedStatement statement = connection.prepareStatement(registerString);
            statement.setInt(1, studentID);
            statement.setString(2, firstName);
            statement.setString(3, lastName);
            statement.setInt(4, age);
            statement.setInt(5, grade);
            statement.executeUpdate();
            
            // 数据库操作成功后更新UI并清空输入框
            warning.setText("Registration Completed!");
            warning.setVisible(true);
            firstNameTF.setText("");
            lastNameTF.setText("");
            ageTF.setText("");
            GradeTF.setText("");
            // ...重置其他状态
        }catch(Exception e){
            e.printStackTrace();
            warning.setText("Registration Failed!");
            warning.setVisible(true);
        }
    }else{
        warning.setText("Fields are Empty!");
        warning.setVisible(true);
    }
}

额外建议 #

• 对输入框内容增加前置校验，比如判断年龄、年级是否为有效数字，提前拦截非法输入
• 始终使用PreparedStatement代替直接拼接SQL字符串，彻底避免SQL注入风险

内容的提问来源于stack exchange，提问作者Dinira Francisco