NullPointerException error when reading xlsx file using Apache POI and adding contents to List

Question

I have placed an xlsx file within my assets folder as you can see in this image:

But I'm experiencing issues from my activity, as the HashMap retrieved is Null.

The activity:

    public class meal extends Activity {
HashMap<String, List<String>> Meal_category;
List<String> Meal_list;
ExpandableListView Exp_list;
MealAdapter adapter;
dataGenerator dg;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_meal);
    Exp_list = (ExpandableListView) findViewById(R.id.exp_list);
    String pth = "menuaa.xlsx";
    try {
        Meal_category = dg.getMenu(pth);
    } catch (Exception e) {
        e.printStackTrace();
    }
    Meal_list = new ArrayList<String>(Meal_category.keySet());
    adapter = new MealAdapter(this, Meal_category, Meal_list);
    Exp_list.setAdapter(adapter);
}

}

The NullPointerException arrives when creating the Meal_list. Here is my code for the getMenu class in the dg.getMenu, that should normally have content within it. I know this because I ran a test on NetBeans, where I easily referred to "menuaa.xlsx" in this manner, and it worked perfectly:

    FileInputStream file = null;
    try {
        file = new FileInputStream(new File(mpath));
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }

    //creating a workbook instance that can refer to .xls file
    XSSFWorkbook wb=null;
    try {
         wb = new XSSFWorkbook(file);
    } catch (IOException e) {
        e.printStackTrace();
    }

    //create a sheet object
    XSSFSheet sheet = wb.getSheetAt(0);

    //that is for evaluate the cell type
    FormulaEvaluator formulaEvaluator = wb.getCreationHelper().createFormulaEvaluator();

I couldn't refer to it in the same way as I had in Android Studio, so added it to my assets file, as shown above. I access this file from my dataGenerator class as shown below.

     public HashMap<String, List<String>> getMenu(String mpath) throws Exception
{

    HashMap<String, List<String>> MealDetails = new HashMap<String, List<String>>();
    List<String> Chinese_Food = new ArrayList<String>();
    List<String> Muslim_Food = new ArrayList<String>();
    List<String> WesternSet_Food = new ArrayList<String>();
    List<String> MuslimSpecial_Food = new ArrayList<String>();

    InputStream caInput = new BufferedInputStream(context.getAssets().open(
            mpath));

    XSSFWorkbook workbook = new XSSFWorkbook(caInput);

    //create a sheet object
    XSSFSheet sheet = workbook.getSheetAt(0);

    //that is for evaluate the cell type
    FormulaEvaluator formulaEvaluator = workbook.getCreationHelper().createFormulaEvaluator();

    for(Row row : sheet){
        for(Cell cell : row){

            switch(formulaEvaluator.evaluateInCell(cell).getCellType())
            {

                //if cell is a numeric format
                case Cell.CELL_TYPE_NUMERIC:
                    break;
                case Cell.CELL_TYPE_STRING:
                    Log.d("MyMessage", "entered cell string type");
                    if(cell.getStringCellValue().contains("Chinese Meal")){
                        //store name of meal in list
                        int columnNumber = cell.getColumnIndex();
                        int rowNumber = cell.getRow().getRowNum();


                        int foodNumber = rowNumber+1;
                        CellReference mealCell = new CellReference(foodNumber,columnNumber);
                        Row r = sheet.getRow(mealCell.getRow());
                        Cell c = r.getCell(mealCell.getCol());
                        String mealName = c.getStringCellValue();
                        Log.w("MyClassName", mealName);
                        //add name of meal to Chinese Food list
                        Chinese_Food.add(mealName);
                    }

                    //search document for all cells that contain "Muslim Meal"
                    if(cell.getStringCellValue().contains("Muslim Meal")){
                        //store name of meal in list
                        int columnNumber = cell.getColumnIndex();
                        int rowNumber = cell.getRow().getRowNum();


                        int foodNumber = rowNumber+1;
                        CellReference mealCell = new CellReference(foodNumber,columnNumber);
                        Row r = sheet.getRow(mealCell.getRow());
                        Cell c = r.getCell(mealCell.getCol());
                        String mealName = c.getStringCellValue();
                        System.out.println(mealName);
                        Muslim_Food.add(mealName);
                    }

                    //search document for all cells that contain "Western Set Meal"
                    if(cell.getStringCellValue().contains("Western Set Meal")){
                        //store name of meal in list
                        int columnNumber = cell.getColumnIndex();
                        int rowNumber = cell.getRow().getRowNum();


                        int foodNumber = rowNumber+1;
                        CellReference mealCell = new CellReference(foodNumber,columnNumber);
                        Row r = sheet.getRow(mealCell.getRow());
                        Cell c = r.getCell(mealCell.getCol());
                        String mealName = c.getStringCellValue();
                        System.out.println(mealName);
                        WesternSet_Food.add(mealName);
                    }

                    //search document for all cells that contain "Muslim Special"
                    if(cell.getStringCellValue().contains("Muslim Special")){
                        //store name of meal in list
                        int columnNumber = cell.getColumnIndex();
                        int rowNumber = cell.getRow().getRowNum();
                        int foodNumber = rowNumber+1;
                        CellReference mealCell = new CellReference(foodNumber,columnNumber);
                        Row r = sheet.getRow(mealCell.getRow());
                        Cell c = r.getCell(mealCell.getCol());
                        String mealName = c.getStringCellValue();
                        MuslimSpecial_Food.add(mealName);
                    }
                    break;
            }
        }
    }

    MealDetails.put("Chinese Meal", Chinese_Food);
    MealDetails.put("Muslim Meal", Muslim_Food);
    MealDetails.put("Western Special Set", WesternSet_Food);
    MealDetails.put("Muslim Special", MuslimSpecial_Food);

    return MealDetails;
}

Finally, here are my jar files, in case you wanted more content :P

I've followed numerous threads on this but to no avail, with each one bringing me back to square one. I know, a lot of .jar's. I've set up a multiDex for my program to work with.

My Stacktrace:

10-23 16:58:19.594  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.HashMap com.raphaelharel.thoughtforfood.dataGenerator.getMenu(java.lang.String)' on a null object reference
10-23 16:58:19.604  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at com.raphaelharel.thoughtforfood.meal.onCreate(meal.java:33)
10-23 16:58:19.604  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at android.app.Activity.performCreate(Activity.java:5977)
10-23 16:58:19.604  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
10-23 16:58:19.604  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2258)
10-23 16:58:19.604  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2367)
10-23 16:58:19.604  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at android.app.ActivityThread.access$800(ActivityThread.java:148)
10-23 16:58:19.604  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1283)
10-23 16:58:19.604  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at android.os.Handler.dispatchMessage(Handler.java:102)
10-23 16:58:19.604  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at android.os.Looper.loop(Looper.java:135)
10-23 16:58:19.605  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at android.app.ActivityThread.main(ActivityThread.java:5274)
10-23 16:58:19.605  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at java.lang.reflect.Method.invoke(Native Method)
10-23 16:58:19.605  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at java.lang.reflect.Method.invoke(Method.java:372)
10-23 16:58:19.605  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:909)
10-23 16:58:19.605  28881-28881/com.raphaelharel.thoughtforfood W/System.err﹕ at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:704)
10-23 16:58:19.609  28881-28881/com.raphaelharel.thoughtforfood D/AndroidRuntime﹕ Shutting down VM
10-23 16:58:19.613  28881-28881/com.raphaelharel.thoughtforfood E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.raphaelharel.thoughtforfood, PID: 28881
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.raphaelharel.thoughtforfood/com.raphaelharel.thoughtforfood.meal}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Set java.util.HashMap.keySet()' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2305)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2367)
            at android.app.ActivityThread.access$800(ActivityThread.java:148)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1283)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5274)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:909)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:704)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Set java.util.HashMap.keySet()' on a null object reference
            at com.raphaelharel.thoughtforfood.meal.onCreate(meal.java:37)
            at android.app.Activity.performCreate(Activity.java:5977)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2258)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2367)
            at android.app.ActivityThread.access$800(ActivityThread.java:148)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1283)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5274)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:909)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:704)

I definitely think it's an issue with how I'm accessing the xlsx file from Android Studio. Any help is much appreciated!

EDIT: I have run the class without the Excel reading (having manually inputted values to List), and can confirm that the issue lies with my failure to properly read the file.

Answer 1

your dataGenerator is null.

the NullpointerException is here:

Meal_category = dg.getMenu(pth);

first of all create a new object of dataGenerator:

dataGenerator = new dataGenerator();
Meal_category = dg.getMenu(pth);

then it should work.