从数据库动态显示数据到TableView中的单元格中的错误

时间：2018-09-26 21:25:26

标签： sql database javafx nullpointerexception

任何人都可以帮忙吗？ 我想将数据库内容动态显示到FXML文件的TableView中。 当我在任何列数据库中都没有空值时，该代码将起作用。 我希望当数据库列的值为空时，代码应在FXML的TableView中显示空白。

dateOfIssue.setCellValueFactory(new Callback<CellDataFeatures<ObservableList, String>, ObservableValue<String>>() {
                public ObservableValue<String> call(CellDataFeatures<ObservableList, String> param) {
                    return new SimpleStringProperty(param.getValue().get(2).toString());
                }
            });
        studentID.setCellValueFactory(new Callback<CellDataFeatures<ObservableList, String>, ObservableValue<String>>() {
                public ObservableValue<String> call(CellDataFeatures<ObservableList, String> param) {
                    return new SimpleStringProperty(param.getValue().get(3).toString());
                }
            });
        primary.setCellValueFactory(new Callback<CellDataFeatures<ObservableList, String>, ObservableValue<String>>() {
                public ObservableValue<String> call(CellDataFeatures<ObservableList, String> param) {
                    return new SimpleStringProperty(param.getValue().get(0).toString());
                }
            });
        secondary.setCellValueFactory(new Callback<CellDataFeatures<ObservableList, String>, ObservableValue<String>>() {
                public ObservableValue<String> call(CellDataFeatures<ObservableList, String> param) {
                        return new SimpleStringProperty(param.getValue().get(1).toString());

                }
            });

第二行的第二列为null。这是我的错误。

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at library.DatabaseController$4.call(DatabaseController.java:105)
at library.DatabaseController$4.call(DatabaseController.java:103)
at javafx.scene.control.TableColumn.getCellObservableValue(TableColumn.java:578)
at javafx.scene.control.TableColumn.getCellObservableValue(TableColumn.java:563)
at javafx.scene.control.TableCell.updateItem(TableCell.java:644)
at javafx.scene.control.TableCell.indexChanged(TableCell.java:468)
at javafx.scene.control.IndexedCell.updateIndex(IndexedCell.java:116)
at com.sun.javafx.scene.control.skin.TableRowSkinBase.updateCells(TableRowSkinBase.java:533)
at com.sun.javafx.scene.control.skin.TableRowSkinBase.init(TableRowSkinBase.java:147)
at com.sun.javafx.scene.control.skin.TableRowSkin.<init>(TableRowSkin.java:64)
at javafx.scene.control.TableRow.createDefaultSkin(TableRow.java:212)
at javafx.scene.control.Control.impl_processCSS(Control.java:872)
at javafx.scene.Node.processCSS(Node.java:9058)
at javafx.scene.Node.applyCss(Node.java:9155)
at com.sun.javafx.scene.control.skin.VirtualFlow.setCellIndex(VirtualFlow.java:1964)
at com.sun.javafx.scene.control.skin.VirtualFlow.addTrailingCells(VirtualFlow.java:1344)
at com.sun.javafx.scene.control.skin.VirtualFlow.layoutChildren(VirtualFlow.java:1197)
at javafx.scene.Parent.layout(Parent.java:1087)
at javafx.scene.Parent.layout(Parent.java:1093)
at javafx.scene.Parent.layout(Parent.java:1093)
at javafx.scene.Parent.layout(Parent.java:1093)
at javafx.scene.Parent.layout(Parent.java:1093)
at javafx.scene.Scene.doLayoutPass(Scene.java:552)
at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2397)
at com.sun.javafx.tk.Toolkit.lambda$runPulse$29(Toolkit.java:398)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.Toolkit.runPulse(Toolkit.java:397)
at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:424)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:518)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:498)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulseFromQueue(QuantumToolkit.java:491)
at com.sun.javafx.tk.quantum.QuantumToolkit.lambda$runToolkit$403(QuantumToolkit.java:319)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
at java.lang.Thread.run(Thread.java:748)
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at library.DatabaseController$4.call(DatabaseController.java:105)
at library.DatabaseController$4.call(DatabaseController.java:103)
at javafx.scene.control.TableColumn.getCellObservableValue(TableColumn.java:578)
at javafx.scene.control.TableColumn.getCellObservableValue(TableColumn.java:563)
at javafx.scene.control.TableCell.updateItem(TableCell.java:644)
at javafx.scene.control.TableCell.indexChanged(TableCell.java:468)
at javafx.scene.control.IndexedCell.updateIndex(IndexedCell.java:116)
at com.sun.javafx.scene.control.skin.TableRowSkinBase.updateCells(TableRowSkinBase.java:533)
at com.sun.javafx.scene.control.skin.TableRowSkinBase.init(TableRowSkinBase.java:147)
at com.sun.javafx.scene.control.skin.TableRowSkin.<init>(TableRowSkin.java:64)
at javafx.scene.control.TableRow.createDefaultSkin(TableRow.java:212)
at javafx.scene.control.Control.impl_processCSS(Control.java:872)
at javafx.scene.Parent.impl_processCSS(Parent.java:1280)
at javafx.scene.Parent.impl_processCSS(Parent.java:1280)
at javafx.scene.Parent.impl_processCSS(Parent.java:1280)
at javafx.scene.Parent.impl_processCSS(Parent.java:1280)
at javafx.scene.control.Control.impl_processCSS(Control.java:868)
at javafx.scene.Node.processCSS(Node.java:9058)
at javafx.scene.Node.processCSS(Node.java:9051)
at javafx.scene.Node.processCSS(Node.java:9051)
at javafx.scene.Node.processCSS(Node.java:9051)
at javafx.scene.Scene.doCSSPass(Scene.java:545)
at javafx.scene.Scene.access$3600(Scene.java:159)
at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2392)
at com.sun.javafx.tk.Toolkit.lambda$runPulse$29(Toolkit.java:398)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.Toolkit.runPulse(Toolkit.java:397)
at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:424)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:518)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:498)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulseFromQueue(QuantumToolkit.java:491)
at com.sun.javafx.tk.quantum.QuantumToolkit.lambda$runToolkit$403(QuantumToolkit.java:319)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
at java.lang.Thread.run(Thread.java:748)

2 个答案:

答案 0 :(得分：0)

我认为您的问题在下面。如果您的值为null，则显然在访问toString（）时会得到NPE。尝试在调用toString（）之前做一些空检查。

param.getValue().get(1).toString()

答案 1 :(得分：0)

如果ObservableList中的一个包含null，则尝试为此类对象调用toString将导致NullPointerException。我建议使用其他代码将其转换为字符串，例如Objects.toString：

secondary.setCellValueFactory(new Callback<CellDataFeatures<ObservableList, String>, ObservableValue<String>>() {

    @Override
    public ObservableValue<String> call(CellDataFeatures<ObservableList, String> param) {
        return new SimpleStringProperty(Objects.toString(param.getValue().get(1), ""));
    }
});
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