NumberFormatException: For input string: "null" when trying to read an excel file using apache poi

Question

When it comes time for the controller in my javafx program to call my excel reading method I am given this error:

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Node.fireEvent(Node.java:8413)
    at javafx.scene.control.Button.fire(Button.java:185)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
    at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:381)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:417)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
    ... 48 more
Caused by: java.lang.NumberFormatException: For input string: "null"
    at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2043)
    at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
    at java.lang.Double.parseDouble(Double.java:538)
    at java.lang.Double.valueOf(Double.java:502)
    at sample.Tab.setTotal(Tab.java:47)
    at sample.Tab.readFromExcelFile(Tab.java:122)
    at sample.Controller.editTab(Controller.java:121)
    ... 58 more

This is my first javafx project using Apache and I haven't had any trouble with the excel writing method, just the reader. I have gone through my code a few times and can't seem to pinpoint what is causing this error. Be warned, my code may look a little ugly since this is a prototype in addition to me lacking in any hands on experience with Apache, and not much with javafx for that matter.

Here is the relevant code-

Main method:

package sample;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

import org.apache.poi.xssf.usermodel.*;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("TabTrackerUI.fxml"));
        primaryStage.setTitle("The Final Tabs");
        primaryStage.setScene(new Scene(root, 1200, 690));
        primaryStage.show();

        XSSFWorkbook workbook = new XSSFWorkbook();
        XSSFSheet sheet = workbook.createSheet("Customers");
    }


    public static void main(String[] args) {
        launch(args);
    }
}

The class where I create the methods needed for writing and reading an excel file:

public class Tab{
    private String custName;
    private BigDecimal custTotal;
    private String custLast;




    public Tab(String custName, String custTotal, String custLast){
        this.custName = custName;
        this.custTotal = new BigDecimal(custTotal);
        this.custLast = custLast;
    }

    public Tab() {

    }


    //Getters and Setters
    public String getName(){return custName;}
    public BigDecimal getTotal(){return custTotal;}
    public String getLast(){return custLast;}

    public void setName(String name){this.custName = name;}
    public void setTotal(String price){
        double current = Double.valueOf(String.valueOf(getTotal()));
        this.custTotal = BigDecimal.valueOf(Long.parseLong(current + price));
    }
    public void setLast(String item){this.custLast = item;}

    public static void writeExcel(Tab tab, String excelFilePath) throws IOException {
        Workbook workbook = new HSSFWorkbook();
        Sheet sheet = workbook.createSheet();

        int rowCount = 0;

        Row row = sheet.createRow(++rowCount);
        writeTab(tab, row);

        try (FileOutputStream outputStream = new FileOutputStream(excelFilePath)) {
            workbook.write(outputStream);
        }
    }

    private static void writeTab(Tab tab, Row row) {
        Cell cell = row.createCell(1);
        cell.setCellValue(tab.getName());

        cell = row.createCell(2);
        cell.setCellValue(String.valueOf(tab.getTotal()));

        cell = row.createCell(3);
        cell.setCellValue(tab.getLast());
    }
    //Read from excel docs
    public String toString() {
        return String.format("%s - %s - %f", custName, custTotal, custLast);
    }

    private Object getCellValue(Cell cell) {
        switch (cell.getCellType()) {
            case Cell.CELL_TYPE_STRING:
                return cell.getStringCellValue();

            case Cell.CELL_TYPE_BOOLEAN:
                return cell.getBooleanCellValue();

            case Cell.CELL_TYPE_NUMERIC:
                return cell.getNumericCellValue();
            case Cell.CELL_TYPE_ERROR:
                return null;
        }

        return null;
    }

    List<Tab> readFromExcelFile(String excelFilePath) throws IOException {
        List<Tab> listTab = new ArrayList<>();
        FileInputStream inputStream = new FileInputStream(new File(excelFilePath));

        Workbook workbook = new HSSFWorkbook(inputStream);
        Sheet firstSheet = workbook.getSheetAt(0);
        Iterator<Row> iterator = firstSheet.iterator();

        while (iterator.hasNext()) {
            Row nextRow = iterator.next();
            Iterator<Cell> cellIterator = nextRow.cellIterator();
            Tab aTab = new Tab();

            while (cellIterator.hasNext()) {
                Cell nextCell = cellIterator.next();
                int columnIndex = nextCell.getColumnIndex();

                switch (columnIndex) {
                    case 1:
                        aTab.setName((String) getCellValue(nextCell));
                        break;
                    case 2:
                        aTab.setTotal((String) getCellValue(nextCell));
                        break;
                    case 3:
                        aTab.setLast((String) getCellValue(nextCell));
                        break;
                }


            }
            listTab.add(aTab);
        }

        workbook.close();
        inputStream.close();

        return listTab;
    }

}

Controller class where the method is called(the call is temporary for testing):

@FXML
    public void editTab(ActionEvent event) throws IOException {
        Tab reader = new Tab();
        List<Tab> listTabs = reader.readFromExcelFile(excelFilePath);
        System.out.println(listTabs);
    }

And here is a screenshot of the excel file I generated if you need to see the formatting(it only has one entry, this is because I'm really currently focused on getting the reader to read anything right now.).

Answer 1

public BigDecimal getTotal(){return custTotal;} //culprit --here

     public BigDecimal getTotal(){return custTotal;}//culprit --here
        public String getLast(){return custLast;}

        public void setName(String name){this.custName = name;}
        public void setTotal(String price){
            double current = Double.valueOf(String.valueOf(getTotal())); //culprit --here
            this.custTotal = BigDecimal.valueOf(Long.parseLong(current + price));
        }

The reason you are facing NULL pointer issue is because you haven't assigned a value to custTotal hence NULL pointer when your trying to convert to double value here

double current = Double.valueOf(String.valueOf(getTotal()))

Which in turn calls

public BigDecimal getTotal(){return custTotal;} // custTotal is null still

SOLUTION

In your constructor assign custTotal = 0;

 Tab(){
     custTotal = new BigDecimal(0);
 }

Also you will still face an issue here

this.custTotal = BigDecimal.valueOf(Long.parseLong(current + price));

Because price is still of String and your trying to add double and string which will fail change it to the below and it will work

 double dPrice = Double.valueOf(price);
 this.custTotal = BigDecimal.valueOf(current + dPrice);

Hope this help :)