如何將變量傳遞給 SQL 查詢

Question

我正在將一個字符串從一個場景傳遞到另一個場景，兩者都在 JavaFX 中使用不同的控制器，並使用該字符串執行 sql 語句，但出現“檢查與 maria DB 服務器對應的手冊”的錯誤。 我會放下我的相關代碼。 任何幫助，將不勝感激。 menu.fxml ----> MenuController.java AND orderList.fxml ----> OrderListController.java

                FXMLLoader loader = new FXMLLoader(getClass().getResource("orderList.fxml"));
                Parent root = loader.load();
                OrderListController orderListController = loader.getController();
                orderListController.transferMessage(orderRefNo);
                Stage orderListStage = new Stage();
                orderListStage.setScene(new Scene(root));
                orderListStage.show();

public class OrderListController implements Initializable {

    private String orderRefNo;
    public void transferMessage(String message){
        orderRefNo = message;
    }

    public OrderListController() throws SQLException, ClassNotFoundException {
    }
    @Override
    public void initialize(URL location, ResourceBundle resources) {
        try {
            //ResultSet resultSet = connection.createStatement().executeQuery("SELECT * FROM "+orderRefNo+"");
            PreparedStatement preparedStatement = connection.prepareStatement("SELECT * FROM ?");
            preparedStatement.setString(1, orderRefNo);
            ResultSet resultSet = preparedStatement.executeQuery();
            while (resultSet.next()){
                observableList.add(new orderListTableModel(resultSet.getString("ID"), resultSet.getString("FOOD_NAME"), resultSet.getString("QUANTITY"),
                        resultSet.getString("PRICE")));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }

        id_OrderListTableModel.setCellValueFactory(new PropertyValueFactory<>("id"));
        food_OrderListTableModel.setCellValueFactory(new PropertyValueFactory<>("foodName"));
        quantity_OrderListTableModel.setCellValueFactory(new PropertyValueFactory<>("qty"));
        price_OrderListTableModel.setCellValueFactory(new PropertyValueFactory<>("price"));

        orderListTableModel.setItems(null);
        orderListTableModel.setItems(observableList);
    }
}

錯誤代碼

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'null' at line 1
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
    at com.mysql.jdbc.Util.getInstance(Util.java:408)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:944)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3978)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3914)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2530)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2683)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2495)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1903)
    at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2011)
    at sample.OrderListController.initialize(OrderListController.java:37)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2573)
    at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2466)
    at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:2435)
    at sample.MenuController.menuBtnClicked(MenuController.java:107)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
    at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1782)
    at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1670)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Scene$ClickGenerator.postProcess(Scene.java:3589)
    at javafx.graphics/javafx.scene.Scene$ClickGenerator.access$8300(Scene.java:3517)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3885)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.access$1300(Scene.java:3604)
    at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1874)
    at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2613)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:397)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:434)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:433)
    at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
    at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:189)
    at java.base/java.lang.Thread.run(Thread.java:844)

Process finished with exit code 0

順便說一句，這是我的 orderListTableModel

public class orderListTableModel {
    String id, foodName, qty, price;

    public orderListTableModel(String id, String foodName, String qty, String price) {
        this.id = id;
        this.foodName = foodName;
        this.qty = qty;
        this.price = price;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getFoodName() {
        return foodName;
    }

    public void setFoodName(String foodName) {
        this.foodName = foodName;
    }

    public String getQty() {
        return qty;
    }

    public void setQty(String qty) {
        this.qty = qty;
    }

    public String getPrice() {
        return price;
    }

    public void setPrice(String price) {
        this.price = price;
    }
}

Answer 1

不能使用 PreparedStatement 將表名綁定到 SQL 查詢。 PreparedStatement 用於列名，而不是表名。 我知道 orderRefNo 引用了一個 String 對象，但是當您構造查詢時，您仍然將其綁定為SELECT語句中使用的表。

PreparedStatement preparedStatement = connection.prepareStatement("**SELECT * FROM ?**");
preparedStatement.setString(1, orderRefNo);

了解您在查詢中使用 String orderRefNo 作為表名，這是不允許的。 因此你得到一個例外。

您可以采用的另一種方法是將表名連接到您的查詢中，但您永遠不應該這樣做，因為它會使您的代碼容易受到 SQL 注入攻擊。 我再說一遍，不要將您的表名直接連接到您的查詢中。