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BIOB - Binary Object Repository

Build Status Coverage Maven Central

Goal

The goal of this project is to make it easy to store binary data alongside the entities that refer to them.

For example:

  • An avatar image that is linked to the User entity

  • Attachments that are linked to an Issue in an issue tracker

Example Usage

Add dependency

Maven

Use this dependency if you use Maven:

<dependency>
  <groupId>io.github.wimdeblauwe</groupId>
  <artifactId>biob</artifactId>
  <version>${biob.version}</version>
</dependency>

Gradle

For Gradle, use the following dependency:

implementation 'io.github.wimdeblauwe:biob:${biob.version}'

Basic setup

The library is not tied to Spring Boot, but I will use some concepts of Spring Boot to explain it usage.

Suppose you have the following User entity:

@Entity
public class User {

  @Id
  private Long id;
  private String username;

  // further details of class omitted...
}

If you use Spring Data, you will have a repository to persist this in the database:

public interface UserRepository extends CrudRepository<User, Long> {
}

and most likely a Service that uses this repository:

@Service
@Transactional
public class UserServiceImpl implements UserService {

  private final UserRepository repository;

  public UserServiceImpl(UserRepository repository) {
    this.repository = repository;
  }

  public void createUser( String username ) {
    repository.save( new User(null, username) );
  }
}

Extending the User entity

We now extend the User class to store the avatar image of the user. However, we will not store binary file in the database, but only store a reference to the file in the database. The file itself will be stored in a BinaryObjectStorage implementation of which our library has various implementations available.

The type of the reference in the entity can be any primitive or class you want. For this example, we will go for a simple UUID:

@Entity
public class User {

  @Id
  private Long id;
  private String username;
  private UUID avatarId;

  // further details of class omitted...
}

Adding a BinaryObjectRepository

To store a binary file, we create an instance of BinaryObjectRepository:

InMemoryBinaryObjectStorage storage = new InMemoryBinaryObjectStorage(); (1)
BinaryObjectRepository<User, UUID> repository = new BinaryObjectRepository<>( (2)
                                                    UUID::randomUUID, (3)
                                                    (user, uuid) -> user.getId() + "/images/"
                                                                    + uuid.toString(), (4)
                                                    storage); (5)
  1. Creates in memory instance of BinaryObjectStorage

  2. The BinaryObjectRepository needs 2 generic types. The first one is the type of the entity that the binary object is refered from (e.g. User). The second one is the type that is used by the reference itself (e.g. UUID).

  3. The first argument is a function that generates a new object of the type of the reference. This this case, we generate a random UUID.

  4. The second argument is a function that generates the path where the file should be stored. This path will be relative and interpreted by the BinaryObjectStorage implementation as they see fit.

  5. The actual BinaryObjectStorage that will persist the file. This can be in memory, in a folder structure on disk, on an S3 bucket, …​

Updating the UserService

There are now 2 ways to use the BinaryObjectRepository in our service:

  • Inject the full BinaryObjectRepository instance into your service.

  • Inject the BinaryObjectStorage and create the BinaryObjectRepository in the constructor of your service.

This is an example where we inject the backing storage in our service:

@Service
@Transactional
public class UserServiceImpl implements UserService {

  private final UserRepository repository;
  private final BinaryObjectRepository objectRepository;

  public UserServiceImpl(UserRepository repository,
                         BinaryObjectStorage storage) {
    this.repository = repository;
    this.objectRepository = new BinaryObjectRepository<>( UUID::randomUUID, (1)
                                                          (user, uuid) -> user.getId() + "/images/"
                                                                          + uuid.toString(),
                                                          storage);
  }

  public void createUser( String username, MultipartFile avatar ) {
    User user = repository.save( new User(null, username) );

    UUID avatarId = objectRepository.store( user, (2)
                                            getMetadata(avatar),
                                            avatar.getInputStream() );

    user.setAvatarId( avatarId ); (3)
  }

  private BinaryObjectMetadata getMetadata(MultipartFile multipartFile) { (4)
    return new BinaryObjectMetadata(multipartFile.getSize(),
                                    multipartFile.getOriginalFilename(),
                                    multipartFile.getContentType());
  }
}
  1. Create the BinaryObjectRepository in the constructor

  2. Store the binary file. We assume it was uploaded as a MultipartFile via a @Controller for example.

  3. Use the returned avatarId and set it on the entity so it is stored in the database along with the User entity.

  4. The store() method also requires some metadata with is gathered in the BinaryObjectMetadata object.

Backing storage implementations

The project currently has the following backing storages implemented:

In memory

The InMemoryBinaryObjectStorage keeps all binary objects in memory. Its main purpose is testing.

File based

The LocalFileSystemBinaryObjectStorage will store the binary objects on the local filesystem. The generated path for each object that is stored will be relative to the baseDir that is passed at construction time.

Development

Deployment

Release

Release is done via the Maven Release Plugin:

mvn release:prepare

and

mvn release:perform

Note

Before releasing, run export GPG_TTY=$(tty)

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Java library to store binary objects

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