Create Multi-Cloud Application Consuming Object Store Service

You can skip the steps of setting up a basic spring boot project and clone/download the skeletal project from the git repository.

Import the project into the IDE (Eclipse/ Intellij) as maven project.

The project contains the spring boot dependencies for web, configuration processor in pom.xml.
It also contains Application.java class which is the entry point into the application.

Note: If you face any issues while building/importing the application, you can remove the content in .m2 folder and try again.

Edit pom.xml file and add the required dependencies.

Add the below property in properties section. This gson version is required for jclouds to work.

<gson.version>2.6.2</gson.version>

Add the below dependencies in dependencies section.

		<!-- jclouds dependencies -->
		<dependency>
    		<groupId>org.apache.jclouds.provider</groupId>
    		<artifactId>aws-s3</artifactId>
    		<version>2.1.2</version>
		</dependency>
		<dependency>
    		<groupId>org.apache.jclouds.provider</groupId>
    		<artifactId>google-cloud-storage</artifactId>
    		<version>2.1.2</version>
		</dependency>
		<dependency>
			<groupId>com.fasterxml.jackson.core</groupId>
			<artifactId>jackson-databind</artifactId>
		</dependency>
		<dependency>
			<groupId>com.google.guava</groupId>
			<artifactId>guava</artifactId>
			<version>27.0.1-jre</version>
		</dependency>
		<dependency>
			<groupId>commons-fileupload</groupId>
			<artifactId>commons-fileupload</artifactId>
			<version>1.3.3</version>
		</dependency>

jclouds dependencies aws-s3, google-cloud-storage are required to use APIs of jclouds for AWS, GCP respectively.

You can add the dependency based on the Object Store vendor that you are using.

Guava is required by ContextBuilder to build BlobStoreContext and for I/O operations like converting InputStream to ByteStream.

commons-fileupload is required for uploading files.

jackson-databind is required to parse JSON.

In this step you will set the application context based on the environment.

Create package: com.sap.refapps.objectstore.config

Create class ObjectStoreContextInitializer in it.

package com.sap.refapps.objectstore.config;

import java.io.IOException;
import java.util.Optional;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.env.ConfigurableEnvironment;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

public class ObjectStoreContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {

	private static final Logger logger = LoggerFactory.getLogger(ObjectStoreContextInitializer.class);

	private static String activeProfile;

	@Override
	public void initialize(ConfigurableApplicationContext applicationContext) {
		final ConfigurableEnvironment applicationEnvironment = applicationContext.getEnvironment();
		final String profileToActive = getActiveProfile();
		// Active profile is set based on the objectore service connected to.
		// (s3/GCS etc..)
		applicationEnvironment.addActiveProfile(profileToActive);
	}

	/**
	 * This method is used to return the profile name to activate based on
	 * service plans.
	 *
	 * @return profile name
	 */
	public static String getActiveProfile() {
		final String servicePlan = getServicePlan();
		if (servicePlan.equals("s3-standard")) {
			activeProfile = "cloud-aws";
		} else if (servicePlan.equals("gcs-standard")) {
			activeProfile = "cloud-gcp";
		}
		return activeProfile;
	}

	/**
	 * This method is used to parse the service plan name from VCAP_SERVICES
	 *
	 * @return service plan name
	 */
	private static String getServicePlan() {
		Optional<String> servicePlan = Optional.empty();
		final String jsonString = System.getenv("VCAP_SERVICES");
		if (jsonString != null) {
			try {
				ObjectMapper mapper = new ObjectMapper();
				JsonNode root = mapper.readTree(jsonString);
				JsonNode objectstoreNode = root.path("objectstore");

				for (JsonNode node : objectstoreNode) {
					servicePlan = Optional.of(node.path("plan").asText());
				}

			} catch (IOException e) {
				logger.error("Exception occurred: " + e);
			}
		}
		return servicePlan.get();
	}

}

Note: Active profile is set based on the Object Store service connected to (AWS S3/GCS).

getServicePlan() parses the VCAP_SERVICES and finds the service plan used.
This service plan can be used to identify the Object Store provider and set the active profile.
VCAP_SERVICES is the environmental variable, that gets added whenever an application is bound to a service on CF. It contains the credentials required to connect to the service.

In getActiveProfile() method, add more conditional statements based on the service plans of the supported IaaS vendors that you would like to use.

Edit Application.java as shown below. This is required to register the custom ApplicationContextInitializer that you created in the previous step.

package com.sap.refapps.objectstore;

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;

import com.sap.refapps.objectstore.config.ObjectStoreContextInitializer;

@SpringBootApplication  
public class Application {  
  public static void main(String[] args) {  
  new SpringApplicationBuilder(Application.class)  
    .initializers(new ObjectStoreContextInitializer()).run(args);  
  }  
}

You need to create configuration classes depending on the number of cloud providers you are planning to run the application on. This class stores the required credentials and gets the BlobStoreContext by passing these credentials.

If you are using AWS as the infrastructure, then follow Step 5.1.

If you are using GCP as the infrastructure, then follow Step 5.2.

If you want the application to run on both the infrastructures, then follow both Step 5.1 and 5.2.

Step 5.1

Create class AmazonWebServiceConfiguration in com.sap.refapps.objectstore.config package.

package com.sap.refapps.objectstore.config;

import org.jclouds.ContextBuilder;
import org.jclouds.blobstore.BlobStoreContext;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;
import org.springframework.context.annotation.PropertySource;

/**
 * This is AWS Credentials Configuration class
 *
 */

@Profile("cloud-aws")
@Configuration
@ConfigurationProperties(prefix = "vcap.services.objectstore-service.credentials")
@PropertySource("classpath:application.properties")
public class AmazonWebServiceConfiguration {

	private String accessKeyId;
	private String bucket;
	private String secretAccessKey;

	public String getAccessKeyId() {
		return accessKeyId;
	}

	public void setAccessKeyId(final String accessKeyId) {
		this.accessKeyId = accessKeyId;
	}

	public String getBucket() {
		return bucket;
	}

	public void setBucket(final String bucket) {
		this.bucket = bucket;
	}

	public String getSecretAccessKey() {
		return secretAccessKey;
	}

	public void setSecretAccessKey(final String secretAccessKey) {
		this.secretAccessKey = secretAccessKey;
	}

	/**
	 * @return blobStoreContext
	 */
	public BlobStoreContext getBlobStoreContext() {
		return ContextBuilder.newBuilder("aws-s3").credentials(this.getAccessKeyId(), this.getSecretAccessKey())
				.buildView(BlobStoreContext.class);
	}

}

Step 5.2

Create class GoogleCloudPlatformConfiguration in com.sap.refapps.objectstore.config package.

package com.sap.refapps.objectstore.config;

import java.nio.charset.Charset;
import java.util.Base64;

import org.jclouds.ContextBuilder;
import org.jclouds.blobstore.BlobStoreContext;
import org.jclouds.domain.Credentials;
import org.jclouds.googlecloud.GoogleCredentialsFromJson;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;
import org.springframework.context.annotation.PropertySource;

import com.google.common.base.Supplier;

/**
 * This is GCP Credentials Configuration class
 *
 */

@Profile("cloud-gcp")
@Configuration
@ConfigurationProperties(prefix = "vcap.services.objectstore-service.credentials")
@PropertySource("classpath:application.properties")
public class GoogleCloudPlatformConfiguration {

	private String base64EncodedPrivateKeyData;
	private String bucket;

	public String getBase64EncodedPrivateKeyData() {
		return base64EncodedPrivateKeyData;
	}

	public String getBucket() {
		return bucket;
	}

	public void setBase64EncodedPrivateKeyData(final String base64EncodedPrivateKeyData) {
		this.base64EncodedPrivateKeyData = base64EncodedPrivateKeyData;
	}

	public void setBucket(final String bucket) {
		this.bucket = bucket;
	}

	/**
	 * @return blobStoreContext
	 */
	public BlobStoreContext getBlobStoreContext() {
		final byte[] decodedKey = Base64.getDecoder().decode(this.getBase64EncodedPrivateKeyData());
		final String decodedCredential = new String(decodedKey, Charset.forName("UTF-8"));
		Supplier<Credentials> supplierCredential = new GoogleCredentialsFromJson(decodedCredential);
		BlobStoreContext blobStoreContext = ContextBuilder.newBuilder("google-cloud-storage")
				.credentialsSupplier(supplierCredential).buildView(BlobStoreContext.class);

		return blobStoreContext;
	}
}

@ConfigurationProperties is used to inject credential values from VCAP_SERVICES into configuration class. Here, 'objectstore-service' is the name of the objectstore service instance created on CF.

@Profile("cloud-aws") annotation, is used to load the right configuration and service implementation classes based on the active provider. For example, if the active provider is "cloud-aws", then AWS configuration and service classes will be loaded.

In this step you will create a model class for blob file. This class stores the metadata including size, contentType, bucket(container in which the file will be stored), etag (unique identifier) and so on of the blob file that you are trying to upload/download from Object Store.

Create package com.sap.refapps.objectstore.model.

Create class BlobFile in it.

package com.sap.refapps.objectstore.model;

import java.util.Map;

public class BlobFile {  

  private String etag;  
  private String bucket;  
  private String name;  
  private String url;  
  private String lastModified;  
  private String size;  
  private String contentType;  
  private Map<String,String> userMetadata;  

  public BlobFile() {  
  }  

  public BlobFile(String name) {  
    this.name = name;  
  }  

 public BlobFile(String etag, String bucket, String name, String url, String size, String lastModified,  
    String contenType, Map<String, String> userMetadata) {  
    this.etag = etag;  
    this.bucket = bucket;  
    this.name = name;  
    this.url = url;  
    this.size = size;  
    this.lastModified = lastModified;  
    this.contentType = contenType;  
    this.userMetadata = userMetadata;  
  }  

  public Map<String, String> getUserMetadata() {  
    return userMetadata;  
  }  

  public String getContentType() {  
    return contentType;  
  }  

  public String getLastModified() {  
    return lastModified;  
  }  

  public String getSize() {  
    return size;  
  }  

  public String getEtag() {  
    return etag;  
  }  

  public String getBucket() {  
    return bucket;  
  }  

  public String getName() {  
    return name;  
  }  

  public String getUrl() {  
    return url;  
  }  
}  

In this step you will create the REST endpoints for upload, download, delete, list operations.
The service class required by the controller will be created in the next step

Create package com.sap.refapps.objectstore.controller.

Create class ObjectstoreController.

package com.sap.refapps.objectstore.controller;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.Optional;

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.fileupload.FileItemIterator;
import org.apache.commons.fileupload.FileItemStream;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.InputStreamResource;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

import com.google.common.io.ByteStreams;
import com.sap.refapps.objectstore.model.BlobFile;
import com.sap.refapps.objectstore.service.ObjectStoreService;

@RestController
@RequestMapping("/objectstorage.svc/api/v1")
public class ObjectstoreController {

	private ObjectStoreService objectStoreService;
	private static Logger logger = LoggerFactory.getLogger(ObjectstoreController.class);

	@Autowired
	public ObjectstoreController(final ObjectStoreService objectStoreService) {
		this.objectStoreService = objectStoreService;
	}

	/**
	 * @return list of blobfiles Function to get the list of objects in the
	 *         objectStore.
	 */
	@GetMapping("/storage")
	@ResponseBody
	public ResponseEntity<List<BlobFile>> listFiles() {

		List<BlobFile> blobFiles = this.objectStoreService.listObjects();
		return new ResponseEntity<>(blobFiles, HttpStatus.OK);
	}

	/**
	 * @param request
	 * @return Message indicating if the file has been uploaded Function to
	 *         upload objects to objectStore.
	 */
	@PostMapping("/storage")
	public ResponseEntity<String> uploadFile(HttpServletRequest request) throws IOException, FileUploadException {

		// Check if we have a file upload request
		boolean isMultipart = ServletFileUpload.isMultipartContent(request);

		String message = "";
		Optional<FileItemStream> fileItemStream = Optional.empty();
		byte[] byteArray = null;

		if (isMultipart) {

			// Create a new file upload handler
			try {
				ServletFileUpload upload = new ServletFileUpload();
				FileItemIterator iter = upload.getItemIterator(request);
				while (iter.hasNext()) {
					fileItemStream = Optional.of(iter.next());
					try (InputStream inputStream = fileItemStream.get().openStream()) {
						byteArray = ByteStreams.toByteArray(inputStream);
						if (!fileItemStream.get().isFormField()) {
							final String contentType = fileItemStream.get().getContentType();
							message = this.objectStoreService.uploadFile(byteArray, fileItemStream.get().getName(),
									contentType);
						}
					} catch (IOException e) {
						logger.error("Error occurred while uploading the object: " + fileItemStream.get().getName() + e);
					}
				}
			} catch (IOException e) {
				logger.error("Error occurred while uploading the object: " + fileItemStream.get().getName() + e);
			}
		}
		return new ResponseEntity<>(message, HttpStatus.ACCEPTED);
	}

	/**
	 * @param fileName
	 * @return inputStream containing the file Function to get a particular
	 *         objects from objectStore.
	 */
	@GetMapping(value = "/storage/{name:.*}")
	public ResponseEntity<InputStreamResource> getFile(@PathVariable(value = "name") String fileName) {

		if (fileName != null) {
			HttpHeaders respHeaders = new HttpHeaders();

			if (this.objectStoreService.isBlobExist(fileName)) {
				respHeaders.setContentDispositionFormData("attachment", fileName);
				InputStreamResource inputStreamResource = new InputStreamResource(
						this.objectStoreService.getFile(fileName));
				return new ResponseEntity<InputStreamResource>(inputStreamResource, respHeaders, HttpStatus.OK);
			} else {
				return errorMessage(fileName + " does not exist in the container", HttpStatus.NOT_FOUND);
			}
		}

		// Default to 200, when input is missing
		return new ResponseEntity<InputStreamResource>(HttpStatus.OK);
	}

	/**
	 * @param fileName
	 * @return Message indicating if the file has been deleted Function to
	 *         delete an object
	 */
	@DeleteMapping("/storage/{name}")
	public ResponseEntity<String> deleteFile(@PathVariable(value = "name") String fileName) {
		String msg = "Could not delete a null object.";
		if (fileName != null) {
			if (this.objectStoreService.isBlobExist(fileName)) {
				if (this.objectStoreService.deleteFile(fileName)) {
					msg = fileName + " is successfully deleted.";
				} else {
					msg = "Error occurred while deleting the object: " + fileName;
					return new ResponseEntity<>(msg, HttpStatus.INTERNAL_SERVER_ERROR);
				}
			} else {
				msg = fileName + " does not exist in the container";
				return errorMessage(msg, HttpStatus.NOT_FOUND);
			}

		}

		return new ResponseEntity<>(msg, HttpStatus.OK);
	}

	/**
	 * @param message
	 * @param status
	 * @return ResponseEntity with HTTP status,headers and body helper function
	 *         to form the responseEntity
	 */
	private static ResponseEntity errorMessage(String message, HttpStatus status) {
		HttpHeaders headers = new HttpHeaders();
		headers.setContentType(org.springframework.http.MediaType.TEXT_PLAIN);

		return ResponseEntity.status(status).headers(headers).body(message);
	}
}

Following the spring guidelines, create a service interface and separate service implementations for each IaaS provider.

Create package com.sap.refapps.objectstore.service.

Create interface ObjectStoreService.

package com.sap.refapps.objectstore.service;

import java.io.InputStream;
import java.util.List;
import org.springframework.stereotype.Service;
import com.sap.refapps.objectstore.model.BlobFile;

@Service
public interface ObjectStoreService {

	public String uploadFile(byte[] bytes, String name, String contentType);

	public boolean deleteFile(String fileName);

	public InputStream getFile(String fileName);

	public List<BlobFile> listObjects();

	public boolean isBlobExist(String name);
}

Create implementation classes. The repository class required by the services will be created in the next step.

If you are using AWS as the Infrastructure, then follow Step 8.1.

If you are using GCP as the Infrastructure, then follow Step 8.2.

If you want the application to run on both the Infrastructures, then follow both Step 8.1 and 8.2.

Here again use @profile annotation to help the controller decide which implementation to invoke.

Step 8.1

Create AWSObjectStoreService class in the same package.

package com.sap.refapps.objectstore.service;

import java.io.InputStream;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Profile;
import org.springframework.stereotype.Service;

import com.sap.refapps.objectstore.config.AmazonWebServiceConfiguration;
import com.sap.refapps.objectstore.model.BlobFile;
import com.sap.refapps.objectstore.repository.ObjectStoreRepository;

@Profile("cloud-aws")
@Service
public class AWSObjectStoreService implements ObjectStoreService {

	private final AmazonWebServiceConfiguration awsConfig;
	private final ObjectStoreRepository repository;
	private final String containerName;
	private static Logger logger = LoggerFactory.getLogger(AWSObjectStoreService.class);

	@Autowired
	public AWSObjectStoreService(final AmazonWebServiceConfiguration awsConfig, ObjectStoreRepository repository) {
		this.awsConfig = awsConfig;
		this.repository = repository;
		this.containerName = awsConfig.getBucket();
	}

	@Override
	public String uploadFile(byte[] bytes, String fileName, String contentType) {
		repository.setContext(awsConfig.getBlobStoreContext());
		logger.info("Upload started");
		String message = repository.uploadFile(containerName, bytes, fileName, contentType);
		logger.info("upload completed");
		return message;
	}

	public List<BlobFile> listObjects() {
		repository.setContext(awsConfig.getBlobStoreContext());
		List<BlobFile> files = repository.listFiles(containerName);
		return files;
	}

	@Override
	public InputStream getFile(String fileName) {
		repository.setContext(awsConfig.getBlobStoreContext());
		InputStream inputStream = repository.downloadFile(containerName, fileName);
		return inputStream;
	}

	@Override
	public boolean deleteFile(String fileName) {
		repository.setContext(awsConfig.getBlobStoreContext());
		boolean status = repository.deleteFile(containerName, fileName);
		return status;

	}

	@Override
	public boolean isBlobExist(String fileName) {
		repository.setContext(awsConfig.getBlobStoreContext());
		boolean status = repository.isBlobExist(containerName, fileName);
		return status;
	}
}

Step 8.2

Create class GCPObjectStoreService in the same package.

package com.sap.refapps.objectstore.service;

import java.io.InputStream;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Profile;
import org.springframework.stereotype.Service;

import com.sap.refapps.objectstore.config.GoogleCloudPlatformConfiguration;
import com.sap.refapps.objectstore.model.BlobFile;
import com.sap.refapps.objectstore.repository.ObjectStoreRepository;

@Profile("cloud-gcp")
@Service
public class GCPObjectStoreService implements ObjectStoreService {

	private final GoogleCloudPlatformConfiguration gcpConfig;
	private final ObjectStoreRepository repository;
	private final String containerName;
	private static Logger logger = LoggerFactory.getLogger(GCPObjectStoreService.class);

	@Autowired
	public GCPObjectStoreService(final GoogleCloudPlatformConfiguration gcpConfig,
			final ObjectStoreRepository repository) {
		this.gcpConfig = gcpConfig;
		this.repository = repository;
		this.containerName = gcpConfig.getBucket();
	}

	@Override
	public String uploadFile(byte[] bytes, String fileName, String contentType) {
		repository.setContext(gcpConfig.getBlobStoreContext());
		logger.info("Upload started");
		String message = repository.uploadFile(containerName, bytes, fileName, contentType);
		logger.info("upload completed");
		return message;
	}

	public List<BlobFile> listObjects() {
		repository.setContext(gcpConfig.getBlobStoreContext());
		List<BlobFile> listBlobs = repository.listFiles(containerName);
		return listBlobs;
	}

	@Override
	public InputStream getFile(String fileName) {
		repository.setContext(gcpConfig.getBlobStoreContext());
		InputStream inputStream = repository.downloadFile(containerName, fileName);
		return inputStream;
	}

	@Override
	public boolean deleteFile(String fileName) {
		repository.setContext(gcpConfig.getBlobStoreContext());
		boolean blobRemove = repository.deleteFile(containerName, fileName);
		return blobRemove;

	}

	@Override
	public boolean isBlobExist(String fileName) {
		repository.setContext(gcpConfig.getBlobStoreContext());
		boolean blobExist = repository.isBlobExist(containerName, fileName);
		return blobExist;
	}

}

The repository class is common for all the Object Store providers and it deals with the actual business logic. This class makes calls to jclouds API – for example, putBlob(), getBlob() – to perform operation in Object Store.

Create package com.sap.refapps.objectstore.repository.

Create class ObjectStoreRepository.

package com.sap.refapps.objectstore.repository;

import java.io.IOException;
import java.io.InputStream;
import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.jclouds.blobstore.BlobStore;
import org.jclouds.blobstore.BlobStoreContext;
import org.jclouds.blobstore.domain.Blob;
import org.jclouds.blobstore.domain.PageSet;
import org.jclouds.blobstore.domain.StorageMetadata;
import org.jclouds.io.Payload;
import org.jclouds.io.payloads.ByteArrayPayload;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Repository;

import com.sap.refapps.objectstore.model.BlobFile;

@Repository
public class ObjectStoreRepository {

	private BlobStoreContext context;
	private BlobStore blobStore;

	private static Logger logger = LoggerFactory.getLogger(ObjectStoreRepository.class);

	public BlobStoreContext getContext() {
		return context;
	}

	public void setContext(BlobStoreContext context) {
		this.context = context;
	}

	/**
	 * @param bucketName
	 * @param data
	 * @param fileName
	 * @return message
	 */
	public String uploadFile(String bucketName, byte[] bytes, String fileName, String contentType) {

		String message = null;

		try {
			// getting blob store
			blobStore = getContext().getBlobStore();

			// creating payload
			Payload payload = new ByteArrayPayload(bytes);

			// adding user metadata to the blob
			Map<String, String> userMetadata = new HashMap<String, String>();
			userMetadata.put("description", "sample content");

			// creating Blob
			Blob blob = blobStore.blobBuilder(fileName).payload(payload).contentType(contentType)
					.userMetadata(userMetadata).build();

			// Multipart upload is currently not supported since it has an issue
			// with OpenStack Swift.
			// multipart issue:
			// (https://issues.apache.org/jira/browse/JCLOUDS-1064).
			blobStore.putBlob(bucketName, blob);
			message = fileName + " is successfully uploaded.";

		} finally {
			getContext().close();
		}

		return message;
	}

	/**
	 * @param bucketName
	 * @return List<BlobFile>
	 */
	public List<BlobFile> listFiles(String bucketName) {

		List<BlobFile> files = new ArrayList<>();
		PageSet<? extends StorageMetadata> list;

		try {
			// getting blobstore
			blobStore = getContext().getBlobStore();

			// List all files from the bucket
			list = blobStore.list(bucketName);

			if (list != null) {
				// Iterate and form the list to be returned
				for (Iterator<? extends StorageMetadata> it = list.iterator(); it.hasNext();) {
					StorageMetadata storageMetadata = it.next();
					Blob blob = blobStore.getBlob(bucketName, storageMetadata.getName());
					files.add(createBlobFile(blob));
				}
			}
		} finally {
			getContext().close();
		}
		return files;
	}

	/**
	 * @param bucketName
	 * @param fileName
	 * @return InputStream
	 */
	public InputStream downloadFile(String bucketName, String fileName) {

		InputStream inputStream = null;
		try {
			// getting blobstore
			blobStore = getContext().getBlobStore();

			// getting blob
			Blob blob = blobStore.getBlob(bucketName, fileName);

			inputStream = blob.getPayload().openStream();
			logger.info(fileName + " is successfully downloaded.");

		} catch (IOException e) {
			logger.error("Error occurred while downloading the object: " + fileName + e);

		} finally {
			getContext().close();
		}

		return inputStream;
	}

	/**
	 * @param bucketName
	 * @param fileName
	 * @return true/false if the blobfile has been deleted
	 */
	public boolean deleteFile(String bucketName, String fileName) {

		boolean isBlobRemoved = false;
		try {
			// getting blobstore
			blobStore = getContext().getBlobStore();
			// removing blob
			blobStore.removeBlob(bucketName, fileName);

			if (!isBlobExist(bucketName, fileName)) {
				isBlobRemoved = true;
				logger.info(fileName + " is successfully deleted.");
			}
		} finally {
			getContext().close();
		}

		return isBlobRemoved;
	}

	public boolean isBlobExist(String bucketName, String fileName) {

		boolean isExist = false;
		try {
			// getting blobstore
			blobStore = getContext().getBlobStore();
			isExist = blobStore.blobExists(bucketName, fileName);
		} finally {
			getContext().close();
		}
		return isExist;
	}

	/**
	 * @param blob
	 * @return blobFile
	 */
	public static BlobFile createBlobFile(final Blob blob) {
		return new BlobFile(blob.getMetadata().getETag(), blob.getMetadata().getContainer(),
				blob.getMetadata().getName(), blob.getMetadata().getUri().toString(),
				readableFileSize(blob.getMetadata().getSize()), blob.getMetadata().getLastModified().toString(),
				blob.getPayload().getContentMetadata().getContentType(), blob.getMetadata().getUserMetadata());

	}

	/**
	 * @param size
	 * @return decimalformat of size of file along with unit
	 */
	private static String readableFileSize(final long size) {
		if (size <= 0)
			return "0";
		final String[] units = new String[] { "B", "KB", "MB", "GB", "TB" };
		int digitGroups = (int) (Math.log10(size) / Math.log10(1024));
		return new DecimalFormat("#,##0.#").format(size / Math.pow(1024, digitGroups)) + " " + units[digitGroups];
	}

}

Create a file manifest.yml in the root folder of the project.

Add the below content to the file.

applications:
- name: objectstore-sample-svc
  host: <unique ID>-objectstore-sample-svc
  memory: 2G
  buildpack: https://github.com/cloudfoundry/java-buildpack.git
  path: target/objectstore-sample-1.0.0.jar
  services:
    - objectstore-service

Provide a unique ID in the host for the application. The host name has to be unique across the Cloud Foundry landscape.
The service objectstore-service will be created in the next step.

In this step you will create an Object Store service, build and deploy the application on Cloud Foundry.

The steps below should be performed in a command prompt or terminal.

1. Log into Cloud Foundry, enter your username and password, and select the org, space when prompted.

   cf api <api>
   cf login
   

   api is the URL of the Cloud Foundry landscape that you are trying to connect to.

2. Look for the objectstore service in the market place, and view the available plans.

   cf marketplace
   

3. Create service instance.

   service-plan is s3-standard for AWS.

   service-plan is gcs-standard for GCP.

   cf create-service objectstore <service-plan> objectstore-service
   

4. Move to the folder that contains pom.xml, and then build and push the application to Cloud Foundry.

   mvn clean install
   cf push
   

   Note: If you face any issues while building/importing the application, you can clear the content in .m2 folder and try again.

Postman Client can be used to test / access the REST API endpoints.

Upload a file

POST <application URL>/objectstorage.svc/api/v1/storage/

Request Body: form-data with key-value pair. Pass the name of the key as file, select file in the dropdown, too. Value is path of the file. You can create a txt file with some data to test.

On a successful upload operation, you will the get the below response:

• Status: 202
• Response Body: <uploaded_filename> is successfully uploaded

List all the files

GET <application URL>/objectstorage.svc/api/v1/storage/

Content-Type: application/json

On a successful get operation, you will the get the below response:

• Status: 200

• Response Body:

  [
    {   
        "etag": "\"79ab51ca348ea601be38845914646c66-1\"",
        "bucket": "hcp-3752ce5a-242e-40a6-801e-3752cf9bd075",
        "name": "sample.docx",
        "url": "https://hcp-3752ce5a-242e-40a6-801e-3752cf9bd075.s3-eu-central-1.amazonaws.com/sample.jpg",
        "lastModified": "Thu Nov 08 08:06:21 UTC 2018",
        "size": "1.4 MB",
        "contentType": "binary/octet-stream",
        "userMetadata": {
            "description": "sample content"
        }
    },
    {
          "etag": "\"423e78a36c57db87f359b2a1b8294beb-1\"",
          "bucket": "hcp-3752ce5a-242e-40a6-801e-3752cf9bd075",
          "name": "resume.pdf",
          "url": "https://hcp-3752ce5a-242e-40a6-801e-3752cf9bd075.s3-eu-central-1.amazonaws.com/resume.pdf",
          "lastModified": "Thu Nov 08 08:07:45 UTC 2018",
          "size": "964.6 KB",
          "contentType": "application/pdf",
          "userMetadata": {
              "description": "sample content"
          }
      }
    ...
  
  ]
  

Download a file

GET <application URL/objectstorage.svc/api/v1/storage/{name}

By hitting this URL, the object will get downloaded into the local system. So please open the URL in any browser rather than Postman to test it.

Delete a file

DELETE <application URL>/objectstorage.svc/api/v1/storage/{name}

On a successful delete operation, you will the get the below response:

• Status: 200

• Response Body: deleted from ObjectStore.

Follow the steps below to extend the application to work with other cloud providers.

1. Add the required jclouds dependency in pom.xml

2. Create configuration class for the provider by checking the required credentials in VCAP_SERVICES.

3. Create service class implementing objectStoreService interface.

4. Add the conditional statements in ObjectStoreContextInitializer class to set the active profile based on service plan.

Source code of the application that works on AWS, GCP and OpenStack is published in git repository.