Why am i getting NullPointerException when i try to save image?

Question

I am trying to save image in my app. But i am getting null pointer exception when i try to persist image object. Here is my Image class:

 @PersistenceCapable
 public class ImageObject {

     @PrimaryKey
     @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
     private Key key;

     @Persistent
     private String title;

     @Persistent
     private Blob image;

     public ImageObject(){}

 //     all getters and setters
 }

Following is my servlet code which is giving exception:

    resp.setContentType("text/html");
    PrintWriter out = resp.getWriter();
    PersistenceManager pm = PMF.get().getPersistenceManager();
    Map<String, List<BlobKey>> blobs = blobstoreService.getUploads(req);
    List<BlobKey> blobKeyList = blobs.get("upload_img_form_input");
    BlobKey blobKey = blobKeyList.get(0);
    String keyString = req.getParameter("upload_img_form_key");

    Key key = KeyFactory.createKey(ImageObject.class.getSimpleName(), keyString);
    Image img = ImagesServiceFactory.makeImageFromBlob(blobKey);
    ImageObject imgObj = new ImageObject();
    imgObj.setKey(key);
    imgObj.setTitle(keyString);
    imgObj.setImage(img.getImageData());
// i am getting exception at this line where i am trying to persist 
    pm.makePersistent(imgObj);

Can anybody please tell me why am i getting this NullPointerException? Thanks in advance.

Well `imgObj` isn't null and you've said below that `pm` isn't null, so you're best bet is to step through `pm.makePersistent()` and see which field in `imgObj` is causing the problem. Adding the relevant parts of the stack trace might be useful here too. — Windle, Oct 23 '12 at 15:19
img.getImageData() is null. This is the blobkey i am getting . why is img.getImageData() null? Am i not fetcing img in right way? — Piscean, Oct 23 '12 at 15:25

score 0 · Answer 1 · edited Oct 23 '12 at 15:26

0

the only way you could have a Npe on this line :

pm.makePersistent(imgObj);

is when pm is null

you should check that part :

PersistenceManager pm = PMF.get().getPersistenceManager();

is your persistence.xml in classpath ?

edited Oct 23 '12 at 15:26

andrewsi

10,807
132
35
51

answered Oct 23 '12 at 15:09

gjambet

369
5
13

i printed pm and this is shown "org.datanucleus.store.appengine.jdo.DatastoreJDOPersistenceManager@1367f48c". which means atleast its not null – Piscean Oct 23 '12 at 15:13
i am persisting a lot of object in other servlets using same line of code. and its working fine. I think its something else. – Piscean Oct 23 '12 at 15:13
could you add your stacktrace ? :D – gjambet Oct 23 '12 at 15:20
this is what i am getting in my console: Exception error: java.lang.NullPointerException nothing else – Piscean Oct 23 '12 at 15:30

score 0 · Answer 2 · answered Aug 26 '14 at 08:22

In my experience, img.getImageData() returns null when you get the image from ImagesServiceFactory.makeImageFromBlob without applying any transformation to it. If you want to get the bytes from the blob without doing any image transformation, you don't actually need the image service and you will just have to fetch the data from the blob store. I tried this code from a blog post and it works well.

public static byte[] readBlobFully(BlobKey blobKey) {

    BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService();
    BlobInfo blobInfo = new BlobInfoFactory().loadBlobInfo(blobKey);

    if (blobInfo == null)
        return null;

    if (blobInfo.getSize() > Integer.MAX_VALUE)
        throw new RuntimeException("This method can only process blobs up to " + Integer.MAX_VALUE + " bytes");

    int blobSize = (int) blobInfo.getSize();
    int chunks = (int) Math.ceil(((double) blobSize / BlobstoreService.MAX_BLOB_FETCH_SIZE));
    int totalBytesRead = 0;
    int startPointer = 0;
    int endPointer;
    byte[] blobBytes = new byte[blobSize];

    for (int i = 0; i < chunks; i++) {

        endPointer = Math.min(blobSize - 1, startPointer + BlobstoreService.MAX_BLOB_FETCH_SIZE - 1);

        byte[] bytes = blobstoreService.fetchData(blobKey, startPointer, endPointer);

        for (int j = 0; j < bytes.length; j++)
            blobBytes[j + totalBytesRead] = bytes[j];

        startPointer = endPointer + 1;
        totalBytesRead += bytes.length;
    }

    return blobBytes;
}

Why am i getting NullPointerException when i try to save image?

2 Answers2