Uploading a blob from a client java application

Question

I currently have the following problem:

I would like to upload a Blob to the Google Blobstore from my client Java application. In the Blobstore documentation (https://cloud.google.com/appengine/docs/java/blobstore/) is described how to do this with a form with which the Blob is uploaded by using a FileChooser.

However, I would like to do this from my code, but I do not know how to convert the Object to a Blob in Java. I would like to pass the generated Blob in a HttpURLConnection, and I have created the classes for this on the Google App Engine.

So my question is: how can I upload a Blob from a client java application?

Note: in my case I would like to upload a JavaFX Image as a Blob, but I think this question could be asked in general.

UPDATE 1: Using the FileService could be the solution, as @TejjD kindly pointed out. However, the Files API is going to be deprecated and is therefore not useful.

UPDATE 2: I am using the following code on the server:

@Override
public void doPost(HttpServletRequest req, HttpServletResponse res)
        throws ServletException, IOException {

    //Check if there is a parameter for the outfit id
     try {
        if (!req.getParameter("id").isEmpty() && Functions.isInteger(req.getParameter("id"))) {

            //Check if the requested id exists in the Cloud SQL database
            Connection conn = ConnectionManager.connectToCloudSQL();
            GetQueryBuilder query = DataManager.executeGet(conn, req, "outfit");

            //Check result
            if (query.getResultSet() == null) {
                throw new Exception("The Outfit object with the requested ID is not yet present in the Cloud SQL database");
            }

            Map<String,List<BlobKey>> blobs = blobstoreService.getUploads(req);
            BlobKey blobKey = blobs.get("image").get(0);

            if (blobKey == null) {
                throw new Exception("No blobkey specified");
            } 
            else {

               //First create a checksum from the file
               String checkSum = this.buildCheckSum(blobKey);

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

               //Create new outfit object
               int outfitId = Integer.parseInt(req.getParameter("id"));
               OutfitExtension outfit = new OutfitExtension();
               outfit.setId(outfitId);
               outfit.setImage(blobKey);
               outfit.setCheckSum(checkSum);

               pm.makePersistent(outfit);

            }
        }
        else {
            throw new Exception("An outfit ID needs to be added to the HTTP request and should be from type Integer only.");
        }
    } catch (Exception e) {
        res.sendError(HttpServletResponse.SC_BAD_REQUEST, "Bad request: "+e.getMessage());
    }

}

This code is run when some URL is called (I have connected this in the web.xml). As you can see in the code, it is about blobstoreService.getUploads(req). How can I post Blob directly in which it is recognized as a upload?

Thanks for your comment! However, I have linked to that information myself. What extra info does it give me about this question? — bashoogzaad
– bashoogzaad, Commented Apr 15, 2015 at 7:53

Community · Accepted Answer · 2017-05-23 10:26:52Z

1

This is a tricky one, I would advise you to perhaps have a look at this

However, I am inserting a code snippet that might answer your question in terms of you wanting to upload via code.

public static BlobKey toBlobstore(Blob imageData) throws FileNotFoundException, FinalizationException, LockException, IOException {
    if (null == imageData)
        return null;

    // Get a file service
    FileService fileService = FileServiceFactory.getFileService();

    // Create a new Blob file with mime-type "image/png"
    AppEngineFile file = fileService.createNewBlobFile("image/jpeg");// png

    // Open a channel to write to it
    boolean lock = true;
    FileWriteChannel writeChannel = fileService.openWriteChannel(file, lock);

    // This time we write to the channel directly
    writeChannel.write(ByteBuffer.wrap
        (imageData.getBytes()));

    // Now finalize
    writeChannel.closeFinally();
    return fileService.getBlobKey(file);
}

UPDATE: (For POST method):

// file Upload.java

import java.io.IOException;
import java.util.List;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.google.appengine.api.blobstore.BlobKey;
import com.google.appengine.api.blobstore.BlobstoreService;
import com.google.appengine.api.blobstore.BlobstoreServiceFactory;

public class Upload extends HttpServlet {
    private BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService();

    @Override
    public void doPost(HttpServletRequest req, HttpServletResponse res)
        throws ServletException, IOException {

        Map<String, List<BlobKey>> blobs = blobstoreService.getUploads(req);
        List<BlobKey> blobKeys = blobs.get("myFile");

        if (blobKeys == null || blobKeys.isEmpty()) {
            res.sendRedirect("/");
        } else {
            res.sendRedirect("/serve?blob-key=" + blobKeys.get(0).getKeyString());
        }
    }
}

That is what you can use to parse the image and upload it.

I hope this assists you :)

All the best!

Let me know of the outcome.

Good luck

edited May 23, 2017 at 10:26

CommunityBot

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answered Apr 15, 2015 at 7:56

TejjD

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4 Comments

bashoogzaad Over a year ago

Thanks for your answer @TejjD, appreciate it! However, where can I specify the URL to which the write needs to be done? Also, the FileService is deprecated, so I am not keen on using that.

TejjD Over a year ago

No problem at all. Glad I could shed some light. Where do you wish for it to be written to?

bashoogzaad Over a year ago

I would like to write it to the Blobstore using a POST url connection, see my updated question.

TejjD Over a year ago

Alright I see what you mean. I have updated my answer, I am working on incorporating what the api, on the link you have already provided, says. I will get back to you on a solution as soon as possible :), I just had a look at your "Update 2" I will use that in finding a solution for you. Thanks

ozarov · Accepted Answer · 2015-04-15 15:41:17Z

0

Any reason for not using Google Cloud storage instead of blobstore? See https://cloud.google.com/storage/docs/json_api/v1/libraries for information about the GCS standard library or https://github.com/GoogleCloudPlatform/appengine-gcs-client for a more convenient access from App Engine.

answered Apr 15, 2015 at 15:41

ozarov

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