为什么将bitmap压缩成JPEG会出现null指针异常？

Question

I am trying to store my bitmap images into a jpeg file in the Items directory. However when trying to compress the bitmap into a JPEG using the compress () I receive a null pointer exception. I have tried debugging and have found that the Items directory I try to create fails, therefore no directory is created. Also, the bitmap is not null.

I cannot seem to find the issue as to why the directory is not created & don't know if that's the reason when compressing my bitmap I get a null pointer exception. I have tried asking permission for storage but that doesn't fix the problem.

Update : I now have been able to create the Items directory however I still get a null pointer exception when compressing the Bitmap.

Code that tries to save bitmap to the Items directory:

public void saveBitmap () {
    boolean dirCreated;
    askForPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE, STORAGE_PERMISSION_CODE);

    File filePath = Environment.getExternalStorageDirectory ();
        File dir = new File (filePath.getAbsolutePath() + "/Items");

        if (!dir.exists ()) {
            try {
                dirCreated = dir.mkdir();

                if (!dirCreated) {
                    Log.d ("notCreated", "the directory has failed");
                }

            } catch (SecurityException e) {
                e.printStackTrace();
            }

        } else {
            Log.d ("dirExists", "the directory already exists");//I receive this in the Log cat
        }

        file = new File (dir, name + ".jpg");
        Log.d ("filey", "file has been created");//I receive this in the log cat

        try {
            outputStream = new FileOutputStream(file);
        } catch (FileNotFoundException e) {
            e.printStackTrace ();
        }

        if (bitmap != null) {
            Log.d ("bitty", "the bimap is not null");//I receive this in the log cat
        }

        bitmap.compress (Bitmap.CompressFormat.JPEG, 0, outputStream);

}

Code that converts my resource into a bitmap:

public void convertToBitmap () {
    bitmap = BitmapFactory.decodeResource(context.getResources(), resourceId);

}

Code that asks permission for storage:

public void askForPermission (String permission, int requestCode) {
    if (isStoragePermissionGranted()) {
        ActivityCompat.requestPermissions((Activity) context, new String [] {permission}, requestCode);
    } else {
        Toast.makeText (context, "Permission already granted", Toast.LENGTH_SHORT)
                .show();

    }
}

public void onRequestPermissionsResult (int requestCode, String [] permissions, int [] grantResults) {
    super.onRequestPermissionsResult (requestCode, permissions, grantResults);

    if (requestCode == STORAGE_PERMISSION_CODE) {
        if (grantResults.length > 0 && grantResults [0] == PackageManager.PERMISSION_GRANTED) {
            Toast.makeText(context, "Storage Permission Granted", Toast.LENGTH_SHORT);
        } else {
            Toast.makeText(context, "Storage Permission Denied", Toast.LENGTH_SHORT);
        }
    }


}

public boolean isStoragePermissionGranted () {

    if (ContextCompat.checkSelfPermission(context, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
        Toast.makeText(context, "permission granted", Toast.LENGTH_SHORT)
                .show();
        return true;
    }

    return false;
}

Manifest file:

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

Error I receive:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapps.myapplication/com.myapps.myapplication.grocery_item}: java.lang.NullPointerException
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3374)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3513)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2109)
    at android.os.Handler.dispatchMessage(Handler.java:107)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7682)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:516)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
 Caused by: java.lang.NullPointerException
    at android.graphics.Bitmap.compress(Bitmap.java:1407)
    at com.myapps.myapplication.BitmapFiles.saveBitmap(BitmapFiles.java:86) //THIS IS THE LINE OF CODE CAUSING THE EXCEPTION
    at com.myapps.myapplication.BitmapFiles.<init>(BitmapFiles.java:40)
    at com.myapps.myapplication.MyDatabaseHelper.createBitmapFiles(MyDatabaseHelper.java:40)
    at com.myapps.myapplication.MyDatabaseHelper.upgradeDatabase(MyDatabaseHelper.java:35)
    at com.myapps.myapplication.MyDatabaseHelper.onUpgrade(MyDatabaseHelper.java:63)
    at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:417)
    at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:341)
    at com.myapps.myapplication.grocery_item.accessDataBase(grocery_item.java:35)
    at com.myapps.myapplication.grocery_item.onCreate(grocery_item.java:20)
    at android.app.Activity.performCreate(Activity.java:7815)
    at android.app.Activity.performCreate(Activity.java:7804)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1318)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3349)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3513) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2109) 
    at android.os.Handler.dispatchMessage(Handler.java:107) 
    at android.os.Looper.loop(Looper.java:214) 
    at android.app.ActivityThread.main(ActivityThread.java:7682) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:516) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950) 

Answer 1

Check to make sure outputStream is not null, compress() will throw a NullPointerException() if the output stream is null.

Answer 2

as i see in Null Pointer Exception when trying to compress Bitmap you need to make something like this:

Bitmap decoded = BitmapFactory.decodeStream(new ByteArrayInputStream(outputStream .toByteArray()));