Sample of a CUBA Storage for Google Cloud Storage - very similar to the supplied AWS S3 one

GoogleCloudFileStorage.java

package com.sample;

import com.google.cloud.storage.*;
import com.haulmont.bali.util.Preconditions;
import com.haulmont.cuba.core.app.FileStorageAPI;
import com.haulmont.cuba.core.entity.FileDescriptor;
import com.haulmont.cuba.core.global.Configuration;
import com.haulmont.cuba.core.global.FileStorageException;
import com.metanube.metai4.google.service.GoogleConfig;
import org.apache.commons.lang3.StringUtils;

import javax.annotation.PostConstruct;
import javax.inject.Inject;
import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.util.Calendar;
import java.util.Date;

import static com.haulmont.bali.util.Preconditions.checkNotNullArgument;

public class GoogleCloudFileStorage implements FileStorageAPI {
    @Inject protected Configuration configuration;
    GoogleConfig googleConfig;
    Storage storage;

    public GoogleCloudFileStorage() {
        storage = StorageOptions.getDefaultInstance().getService();
    }

    @PostConstruct
    public void init() {
        googleConfig = configuration.getConfig(GoogleConfig.class);
    }

    @Override
    public long saveStream(FileDescriptor fileDescr, InputStream inputStream) throws FileStorageException {
        Preconditions.checkNotNullArgument(fileDescr.getSize());
        BlobId blobId = getBlobId(fileDescr);
        Blob blob = storage.create(BlobInfo.newBuilder(blobId).build(), inputStream);
        return blob.getSize();
    }

    @Override
    public void saveFile(FileDescriptor fileDescr, byte[] data) throws FileStorageException {
        checkNotNullArgument(data, "File content is null");
        BlobId blobId = getBlobId(fileDescr);
        storage.create(BlobInfo.newBuilder(blobId).build(), data);
    }

    @Override
    public void removeFile(FileDescriptor fileDescr) throws FileStorageException {
        storage.delete(getBlobId(fileDescr));
    }

    @Override
    public InputStream openStream(FileDescriptor fileDescr) throws FileStorageException {
        return new ByteArrayInputStream(getBlob(fileDescr).getContent());
    }

    @Override
    public byte[] loadFile(FileDescriptor fileDescr) throws FileStorageException {
        Blob blob = getBlob(fileDescr);
        return blob.getContent();
    }

    @Override
    public boolean fileExists(FileDescriptor fileDescr) throws FileStorageException {
        return getBlob(fileDescr) != null;
    }

    protected String resolveFileName(FileDescriptor fileDescr) {
        return getStorageDir(fileDescr.getCreateDate()) + "/" + getFileName(fileDescr);
    }

    /**
     * INTERNAL. Don't use in application code.
     */
    protected Blob getBlob(FileDescriptor fileDescriptor) {
        return getBlob(getBlobId(fileDescriptor));
    }

    protected Blob getBlob(BlobId blobId) {
        return storage.get(blobId);
    }

    protected BlobId getBlobId(FileDescriptor fileDescr) {
        return BlobId.of(googleConfig.getFileStorageBucket(), resolveFileName(fileDescr));
    }

    protected String getStorageDir(Date createDate) {
        Calendar cal = Calendar.getInstance();
        cal.setTime(createDate);
        int year = cal.get(Calendar.YEAR);
        int month = cal.get(Calendar.MONTH) + 1;
        int day = cal.get(Calendar.DAY_OF_MONTH);

        return String.format("%d/%s/%s",
                year, StringUtils.leftPad(String.valueOf(month), 2, '0'), StringUtils.leftPad(String.valueOf(day), 2, '0'));
    }

    protected String getFileName(FileDescriptor fileDescriptor) {
        if (StringUtils.isNotBlank(fileDescriptor.getExtension())) {
            return fileDescriptor.getId().toString() + "." + fileDescriptor.getExtension();
        } else {
            return fileDescriptor.getId().toString();
        }
    }
}