"Resumable Upload" with "Signed URL" on Google Cloud Storage using Java

Regarding the first point, yes, the blob.writer(...)method handles resumable uploads automatically. Unfortunately, this method cannot be called from a signed URL, but can only upload files directly from the byte stream.

However, as you mentioned, there are other ways to create resumable uploads from signed URLs, e.g. using PUTmethod seems like a good workaround.

What I do is:

1. Create a signed URL using the "PUT" method . You can do this by specifying SignUrlOption , and I specified a service account in the bucket with the required permissions.

2. Use URLFetch to throw an HTTP request to this signed URL. I believe e.g. you can't use the curl command directly, and the UrlFetch API does the trick.

3. Add the uploadType=resumable header to the urlFetchHTTP request. See this documentation for how it works and other parameters and information.

4. I configured URLFetchto make an asynchronous call to the signed URL as I thought it would be more convenient when uploading large files.

Example code used in App Engine handler:

package com.example.storage;

import java.io.IOException;
import java.io.FileInputStream;
import java.util.Properties;
import java.util.concurrent.TimeUnit;
import java.util.HashMap;
import java.util.Map;
import java.nio.charset.StandardCharsets;

import java.net.URL;

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

// Cloud Storage Imports
import com.google.cloud.storage.Bucket;
import com.google.cloud.storage.BucketInfo;
import com.google.cloud.storage.Storage;
import com.google.cloud.storage.StorageOptions;
import com.google.cloud.storage.Blob;
import com.google.cloud.storage.BlobId;
import com.google.cloud.storage.BlobInfo;
import com.google.cloud.storage.Storage.SignUrlOption;
import com.google.auth.oauth2.ServiceAccountCredentials;
import com.google.cloud.storage.HttpMethod;

// Url Fetch imports
import com.google.appengine.api.urlfetch.HTTPMethod;
import com.google.appengine.api.urlfetch.HTTPRequest;
import com.google.appengine.api.urlfetch.URLFetchService;
import com.google.appengine.api.urlfetch.URLFetchServiceFactory;
import com.google.appengine.api.urlfetch.HTTPHeader;

@WebServlet(name = "MainStorage", value = "/")
public class MainStorage extends HttpServlet {

        @Override
        public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
                // Bucket parameters 
                String bucketName = "MY-BUCKET-NAME";
                String blobName = "MY-BLOB-NAME";
                String keyPath = "/PATH-TO-SERVICE-ACCOUNT-KEY/key.json";

                BlobId blobId = BlobId.of(bucketName, blobName);
                Storage storage = StorageOptions.getDefaultInstance().getService();

                // Create signed URL with SignUrlOptions
                URL signedUrl = storage.signUrl(BlobInfo.newBuilder(bucketName, blobName).build(), 14, TimeUnit.DAYS,
                                                SignUrlOption.signWith(ServiceAccountCredentials.fromStream(new FileInputStream(keyPath))),
                                                SignUrlOption.httpMethod(HttpMethod.PUT));

                // Contents to upload to the Blob
                String content = "My-File-contents";

                // Build UrlFetch request
                HTTPRequest upload_request = new HTTPRequest(signedUrl, HTTPMethod.PUT);
                upload_request.setPayload(content.getBytes(StandardCharsets.UTF_8));

                // Set request to have an uploadType=resumable
                HTTPHeader set_resumable = new HTTPHeader("uploadType", "resumable");
                upload_request.setHeader(set_resumable);
                URLFetchService fetcher = URLFetchServiceFactory.getURLFetchService();

                // Do an asynchronous call to the signed URL with the contents
                fetcher.fetchAsync(upload_request);

                // Return response to App Engine handler call
                response.setContentType("text/plain");
                response.getWriter().println("Hello Storage");
        }
}

There may be a better way to do this, but I believe it gives an idea of ​​how to do this type of application.