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Preface

Project metadata

1. Working with Spring Stores

The goal of the Spring Content is to make it easy to create applications that manage content such as documents, images and video by significantly reducing the amount of boilerplate code that the Developer must create for themselves. Instead, the Developer provides interfaces only that declare the intent for the content-related functionality. Based on these, and on class-path dependencies, Spring Content is then able to inject storage-specific implementations.

Important

This chapter explains the core concepts and interfaces for Spring Content. The examples in this chapter use Java configuration and code samples for the Spring Content S3 module. Adapt the Java configuration and the types to be extended to the equivalents for the particular Spring Content module that you are using.

1.1. Core concepts

The central interfaces in the Spring Content are Store, AssociativeStore and ContentStore. These interfaces provide access to content streams through the standard Spring Resource API either directly or through association with Spring Data entities.

1.1.1. Store

The simplest interface is the Store interface. Essentially, it is a Spring ResourceLoader that returns instances Spring Resource. It is also generic allowing the Resource’s ID (or location) to be specified. All other Store interfaces extend from Store.

Example 1. Store interface
public interface Store<SID extends Serializable> {

	Resource getResource(SID id);		(1)
}

  1. Returns a Resource handle for the specified id

For example, given a PictureStore that extends Store it is possible to store (retrieve and delete) pictures.

1.1.2. AssociativeStore

AssociativeStore extends from Store allowing Spring Resource’s to be associated with JPA Entities.

Example 2. AssociativeStore interface
public interface AssociativeStore<SID extends Serializable> {

	Resource getResource(SID id);								(1)
	void associate(S entity, PropertyPath path, SID id);		(2)
    void unassociate(S entity, PropertyPath path);				(3)
	Resource getResource(S entity, PropertyPath path);			(4)
}

  1. Returns a Resource handle for the specified id

  2. Associates the Resource id with the Entity entity at the PropertyPath path

  3. Unassociates the Resource at the PropertyPath path from the entity

  4. Returns a handle for the associated Resource at PropertyPath path

For example, given an Entity User with Spring Content annotations, a UserRepository and the PictureStore this time extending AssociativeStore it is possible to store and associate a profile picture for each user.

Example 3. ContentStore interface
@Entity
@Data
public class User {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private Long id;

	private String username;

	@ContentId
	private String profilePictureId;

	@ContentLength
	private Long profilePictureLength
}

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

public interface PictureStore extends AssociativeStore<User, String> {
}

@SpringBootApplication
public class Application {
	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}

	@Bean
	public CommandLineRunner demo(UserRespository repo, PictureStore store) {
		return (args) -> {
			// create a new user
			User jbauer = new User("jbauer");

			// store a picture
			WritableResource r = (WritableResource)store.getResource("/some/picture.jpeg");

			try (InputStream is = new FileInputStream("/tmp/jbauer.jpg")) {
				try (OutputStream os = ((WritableResource)r).getOutputStream()) {
					IOUtils.copyLarge(is, os);
				}
			}

			// associate the Resource with the Entity
			store.associate(jbauer, PropertyPath("profilePicture"), "/some/picture.jpeg");

			// save the user
			repository.save(jbauer);
		};
	}
}

1.2. ContentStore

ContentStore extends AssociativeStore and provides a more convenient API for managing associated content based on java Stream, rather than Resource.

Example 4. ContentStore interface
public interface ContentStore<E, CID extends Serializable> {

	void setContent(E entity, InputStream content); 	(1)
	InputStream getContent(E entity);					(2)
	void unsetContent(E entity);						(3)
}

  1. Stores content and associates it with entity

  2. Returns the content associated with entity

  3. Deletes content and unassociates it from entity

The example above can be refactored as follows:

Example 5. ContentStore interface
@Entity
@Data
public class User {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private Long id;

	private String username;

	@ContentId
	private String profilePictureId;

	@ContentLength
	private Long profilePictureLength
}

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

public interface ProfilePictureStore extends ContentStore<User, String> {
}

@SpringBootApplication
public class Application {
	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}

	@Bean
	public CommandLineRunner demo(UserRepository repository, ProfilePictureStore store) {
		return (args) -> {
			// create a new user
			User jbauer = new User("jbauer");

			// store profile picture
			store.setContent(jbauer, PropertyPath.from("profilePicture"), new FileInputStream("/tmp/jbauer.jpg"));

			// save the user
			repository.save(jbauer);
		};
	}
}

1.3. ReactiveContentStore

ReactiveContentStore is an experimental Store that provides a reactive API for managing associated content based on Mono and Flux reactive API.

Example 6. ReactiveContentStore interface
public interface ReactiveContentStore<E, CID extends Serializable> {

    Mono<S> setContent(S entity, PropertyPath path, long contentLen, Flux<ByteBuffer> buffer);  (1)
    Flux<ByteBuffer> getContentAsFlux(S entity, PropertyPath path);                             (2)
    Mono<E> unsetContent(E entity);                                                             (3)
}

  1. Stores content and associates it with entity

  2. Returns the content associated with entity

  3. Deletes content and unassociates it from entity

The example above can be refactored as follows:

Example 7. ReactiveContentStore interface
@Entity
@Data
public class User {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    private String username;

    @ContentId
    private String profilePictureId;

    @ContentLength
    private Long profilePictureLength
}

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

public interface ProfilePictureStore extends ReactiveContentStore<User, String> {
}

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public CommandLineRunner demo(UserRepository repository, ProfilePictureStore store) {
        return (args) -> {
            // create a new user
            User jbauer = new User("jbauer");

            // store profile picture
            FileInputStream fis = new FileInputStream("/tmp/jbauer.jpg");
            int len = fis.available();
            ByteBuffer byteBuffer = ByteBuffer.allocate(len);
            Channels.newChannel(fis).read(byteBuffer);

            store.setContent(jbauer, PropertyPath.from("profilePicture"), len, Flux.just(byteBuffer)))
                .doOnSuccess(updatedJbauer -> {
                    // save the user
                    repository.save(updatedJbauer).block(Duration.ofSeconds(10));
                }).block(Duration.ofSeconds(10));
        };
    }
}

Currently, S3 is the only storage module that supports this experimental API.

1.3.1. Content Properties

As we can see above content is "associated" by adding additional metadata about the content to the Entity. This additional metadata is annotated with Spring Content annotations. There are several. The only mandatory annotation is @ContentId. Other optional annotations include @ContentLength, @MimeType and @OriginalFileName. These may be added to your entities when you need to capture this additional infomation about your associated content.

When adding these optional annotations it is highly recommended that you correlate the field’s name creating a "content property". This allows for multiple pieces of content to be associated with the same entity, as shown in the following example. When associating a single piece of content this is not necessary but still recommended.

Example 8. Content Property
@Entity
@Data
public class User {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private Long id;

	private String username;

	@ContentId
	private String profilePictureId;			(1)

	@ContentLength
	private Long profilePictureLength

	@MimeType
	private String profilePictureType;

	@OriginalFileName
	private String profilePictureName;

	@ContentId
	private String avatarId;				   (2)

	@ContentLength
	private Long avatarLength

	@MimeType
	private String avatarType;
}

  1. Content property "profilePicture" with id, length, type and original filename

  2. Content property "avatar" with id, length and type

When modeled thus these can then be managed as follows:

InputStream profilePicture = store.getContent(user, PropertyPath.from("profilePicture"));

store.setContent(user, PropertyPath.from("avatar"), avatarStream);

1.3.2. Nested Content Properties

If desired content properties can also be nested, as the following JPA example shows:

Example 9. Nested Content Properties
@Entity
@Data
public class User {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    private String username;

    private @Embedded Images images = new Images();
}

@Embeddable
public class Images {
    @ContentId
    private String profilePictureId;

    @ContentLength
    private Long profilePictureLength

    @MimeType
    private String profilePictureType;

    @OriginalFileName
    private String profileName;

    @ContentId
    private String avatarId;

    @ContentLength
    private Long avatarLength

    @MimeType
    private String avatarType;
}

These can then be managed with forward slash (/) separated property paths:

InputStream profilePicture = store.getContent(user, PropertyPath.from("images/profilePicture"));

store.setContent(user, PropertyPath.from("images/avatar"), avatarStream);

1.3.3. Using Stores with Multiple Spring Content Storage Modules

Using a single Spring Content storage module in your application keeps things simple because all Storage beans will use to that one Spring Content storage module as their implementation. Sometimes, applications require more than one Spring Content storage module. In such cases, a store definition must distinguish between storage technologies by extending one of the module-specific signature Store interfaces.

See Signature Types for the signature types for the storage modules you are using.

Manual Storage Override

Because Spring Content provides an abstraction over storage it is also common to use one storage module for testing but another for production. For these cases it is possible to again include multiple Spring Content storage modules, but use generic Store interfaces, rather than signature types, and instead specify the spring.content.storage.type.default=<storage_module_id> property to manually set the storage implementation to be injected into your Storage beans.

1.3.4. Events

Spring Content emits twelve events. Roughly speaking one for each Store method. They are:

  • BeforeGetResourceEvent

  • AfterGetResourceEvent

  • BeforeAssociateEvent

  • AfterAssociateEvent

  • BeforeUnassociateEvent

  • AfterUnassociateEvent

  • BeforeSetContent

  • AfterSetContent

  • BeforeGetContent

  • AfterGetContent

  • BeforeUnsetContent

  • AfterUnsetContent

Writing an ApplicationListener

If you wish to extend Spring Content’s functionality you can subclass the abstract class AbstractStoreEventListener and override the methods that you are interested in. When these events occur your handlers will be called.

There are two variants of each event handler. The first takes the entity with with the content is associated and is the source of the event. The second takes the event object. The latter can be useful, especially for events related to Store methods that return results to the caller.

Example 10. Entity-based AbstractContentRepositoryEventListener
public class ExampleEventListener extends AbstractContentRepositoryEventListener {

	@Override
	public void onAfterSetContent(Object entity) {
		...logic to inspect and handle the entity and it's content after it is stored
	}

	@Override
	public void onBeforeGetContent(BeforeGetContentEvent event) {
		...logic to inspect and handle the entity and it's content before it is fetched
	}
}

The down-side of this approach is that it does not filter events based on Entity.

Writing an Annotated StoreEventHandler

Another approach is to use an annotated handler, which does filter events based on Entity.

To declare a handler, create a POJO and annotate it as @StoreEventHandler. This tells Spring Content that this class needs to be inspected for handler methods. It iterates over the class’s methods and looks for annotations that correspond to the event. There are twelve handler annotations:

  • HandleBeforeGetResource

  • HandleAfterGetResource

  • HandleBeforeAssociate

  • HandleAfterAssociate

  • HandleBeforeUnassociate

  • HandleAfterUnassociate

  • HandleBeforeSetContent

  • HandleAfterSetContent

  • HandleBeforeGetContent

  • HandleAfterGetContent

  • HandleBeforeUnsetContent

  • HandleAfterUnsetContent

Example 11. Entity-based annotated event handler
@StoreEventHandler
public class ExampleAnnotatedEventListener {

	@HandleAfterSetContent
	public void handleAfterSetContent(SopDocument doc) {
		...type-safe handling logic for SopDocument's and their content after it is stored
	}

	@HandleBeforeGetContent
	public void onBeforeGetContent(Product product) {
		...type-safe handling logic for Product's and their content before it is fetched
	}
}

These handlers will be called only when the event originates from a matching entity.

As with the ApplicationListener event handler in some cases it is useful to handle the event. For example, when Store methods returns results to the caller.

Example 12. Event-based annotated event handler
@StoreEventHandler
public class ExampleAnnotatedEventListener {

	@HandleAfterSetContent
	public void handleAfterGetResource(AfterGetResourceEvent event) {
		SopDocument doc = event.getSource();
		Resource resourceToBeReturned = event.getResult();
		...code that manipulates the resource being returned...
	}
}

To register your event handler, either mark the class with one of Spring’s @Component stereotypes so it can be picked up by @SpringBootApplication or @ComponentScan. Or declare an instance of your annotated bean in your ApplicationContext.

Example 13. Handler registration
@Configuration
public class ContentStoreConfiguration {

	@Bean
	ExampeAnnotatedEventHandler exampleEventHandler() {
		return new ExampeAnnotatedEventHandler();
	}
}

1.3.5. Searchable Stores

Applications that handle documents and other media usually have search capabilities allowing relevant content to be found by looking inside of it for keywords or phrases, so called full-text search.

Spring Content is able to support this capability with it’s Searchable<CID> interface.

Example 14. Searchable interface
public interface Searchable<CID> {

    Iterable<T> search(String queryString);
}

Any Store interface can be made to extend Searchable<CID> in order to extend its capabilities to include the search(String queryString) method. For example:

public interface DocumentContentStore extends ContentStore<Document, UUID>, Searchable<UUID> {
}

...

@Autowired
private DocumentContentStore store;

Iterable<UUID> = store.search("to be or not to be");

For search to return actual results full-text indexing must be enabled. See Fulltext Indexing and Searching for more information on how to do this.

1.3.6. Renderable Stores

Applications that handle files and other media usually also have rendition capabilities allowing content to be transformed from one format to another.

Content stores can therefore optionally also be given rendition capabilities by extending the Renderable<E> interface.

Example 15. Renderable interface
public interface Renderable<E> {

	InputStream getRendition(E entity, String mimeType);
}

Returns a mimeType rendition of the content associated with entity.

Renditions must be enabled and renderers provided. See Renditions for more information on how to do this.

1.4. Creating Content Store Instances

To use these core concepts:

  1. Define a Spring Data entity and give it’s instances the ability to be associated with content by adding @ContentId and @ContentLength annotations

    @Entity
public class SopDocument {
	private @Id @GeneratedValue Long id;
	private String title;
	private String[] authors, keywords;

	// Spring Content managed attribute
	private @ContentId UUID contentId;
	private @ContentLength Long contentLen;
}

  2. Define an interface extending Spring Data’s CrudRepository and type it to the domain and ID classes.

    public interface SopDocumentRepository extends CrudRepository<SopDocument, Long> {
}

  3. Define another interface extending ContentStore and type it to the domain and @ContentId class.

    public interface SopDocumentContentStore extends ContentStore<SopDocument, UUID> {
}

  4. Optionally, make it extend Searchable

    public interface SopDocumentContentStore extends ContentStore<SopDocument, UUID>, Searchable<UUID> {
}

  5. Optionally, make it extend Renderable

    public interface SopDocumentContentStore extends ContentStore<SopDocument, UUID>, Renderable<SopDocument> {
}

  6. Set up Spring to create proxy instances for these two interfaces using JavaConfig:

    @EnableJpaRepositories
@EnableS3Stores
class Config {}
    Note
    		 The JPA and S3 namespaces are used in this example. If you are using the repository and content store abstractions for other databases and stores, you need to change this to the appropriate namespace declaration for your store module.

  7. Inject the repositories and use them

    @Component
public class SomeClass {
	@Autowired private SopDocumentRepository repo;
  	@Autowired private SopDocumentContentStore contentStore;

	public void doSomething() {

		SopDocument doc = new SopDocument();
		doc.setTitle("example");
		contentStore.setContent(doc, new ByteArrayInputStream("some interesting content".getBytes())); # (1)
		doc.save();
		...

		InputStream content = contentStore.getContent(sopDocument);
		...

		List<SopDocument> docs = doc.findAllByContentId(contentStore.findKeyword("interesting"));
		...

	}
}

    1. Spring Content will update the @ContentId and @ContentLength fields

1.5. Patterns of Content Association

Content can be associated with a Spring Data Entity in several ways.

1.5.1. Entity Association

The simplest, allowing you to associate one Entity with one Resource, is to decorate your Spring Data Entity with the Spring Content attributes.

The following example shows a Resource associated with an Entity Dvd.

@Entity
public class Dvd {
	private @Id @GeneratedValue Long id;
	private String title;

	// Spring Content managed attributes
	private @ContentId UUID contentId;
	private @ContentLength Long contentLen;

	...
}

public interface DvdRepository extends CrudRepository<Dvd, Long> {}

public interface DvdStore extends ContentStore<Dvd, UUID> {}

1.5.2. Property Association

Sometimes you might want to associate multiple different Resources with an Entity. To do this it is also possible to associate Resources with one or more Entity properties.

The following example shows two Resources associated with a Dvd entity. The first Resource is the Dvd’s cover Image and the second is the Dvd’s Stream.

@Entity
public class Dvd {
	private @Id @GeneratedValue Long id;
	private String title;

	@OneToOne(cascade = CascadeType.ALL)
	@JoinColumn(name = "image_id")
	private Image image;

	@OneToOne(cascade = CascadeType.ALL)
	@JoinColumn(name = "stream_id")
	private Stream stream;

	...
}

@Entity
public class Image {
	// Spring Data managed attribute
	private @Id @GeneratedValue Long id;

	@OneToOne
	private Dvd dvd;

	// Spring Content managed attributes
	private @ContentId UUID contentId;
	private @ContentLength Long contentLen;
}

@Entity
public class Stream {
	// Spring Data managed attribute
	private @Id @GeneratedValue Long id;

	@OneToOne
	private Dvd dvd;

	// Spring Content managed attributes
	private @ContentId UUID contentId;
	private @ContentLength Long contentLen;
}

public interface DvdRepository extends CrudRepository<Dvd, Long> {}

public interface ImageStore extends ContentStore<Image, UUID> {}

public interface StreamStore extends ContentStore<Stream, UUID> {}

Note how the Content attributes are placed on each property object of on the Entity itself.

When using JPA with a relational database these are typically (but not always) also Entity associations. However when using NoSQL databases like MongoDB that are capable of storing hierarchical data they are true property associations.

Property Collection Associations

In addition to associating many different types of Resource with a single Entity. It is also possible to associate one Entity with many Resources using a java.util.Collection property, as the following example shows.

@Entity
public class Dvd {
	private @Id @GeneratedValue Long id;
	private String title;

	@OneToMany
	@JoinColumn(name = "chapter_id")
	private List<Chapter> chapters;

	...
}

@Entity
public class Chapter {
	// Spring Data managed attribute
	private @Id @GeneratedValue Long id;

	// Spring Content managed attributes
	private @ContentId UUID contentId;
	private @ContentLength Long contentLen;
}

public interface DvdRepository extends CrudRepository<Dvd, Long> {}

public interface ChapterStore extends ContentStore<Chapter, UUID> {}

2. Renditions

2.1. Overview

When enabled, renditions give stores the ability to transform content from one format to another by providing a small set of renderers out-of-the-box.

It also provides an extension point for providing your own renderers.

To enable renditions add the spring-content-renditions or spring-content-renditions-boot-starter dependency to your project. This enables the renditions capability and a small set of renderers that can convert documents of various types to jpeg images based on the apache poi and pdfbox libraries

You can also add the spring-content-docx4j dependency to your project for an additional small set of renderers that can convert documents between Microsoft Word, Adobe PDF and HTML based on the docx4j library.

2.2. Maven Central Coordinates

The maven coordinates for this Spring Content library are as follows:

<dependency>
    <groupId>com.github.paulcwarren</groupId>
    <artifactId>spring-content-renditions</artifactId>
</dependency>

As it is usual to use several Spring Content libraries together importing the bom is recommended:

<dependency>
    <groupId>com.github.paulcwarren</groupId>
    <artifactId>spring-content-bom</artifactId>
    <version>${spring-content-version}</version>
    <type>pom</type>
    <scope>import</scope>
</dependency>

2.3. Annotation-based Configuration

Example 16. Enabling Spring Content Renditions with Java Config
@Configuration
@Import(org.springframework.content.renditions.config.RenditionsConfiguration.class) (1)
@Import(org.springframework.content.docx4j.config.Docx4jConfiguration.class)         (2)
public static class ApplicationConfig {
}

  1. Not required when using spring-content-renditions-boot-starter

  2. Not required when using spring-content-renditions-boot-starter

2.4. Making Stores Renderable

With renditions enabled, Store interfaces can be made Renderable. See Renderable Stores for more information on how to do this.

2.5. Renderers

The spring-content-rendition dependency contributes the following renderer:

  • Pdf To Jpeg

  • Text To Jpeg

  • Word To Jpeg

  • Jpeg To Png

The spring-content-docx4j dependency contributes the following renderer:

  • Word To Html

  • Word To PDF

  • Word To Text

2.6. RenditionProvider Extension Point

Spring Content Renditions offers some common renderers out-of-the-box. However, if you need to provide additional renderers to satisfy your use cases then you can implement the RenditionProvider extension point. This requires you to implement the RenditionProvider interface, mark this implementation as a @Service and ensure that it is contributed as a bean to your application context at runtime.

Example 17. Implementing the RenditionProvider Extension Point
package my.custom.rendition.provider;

@Service    (2)
public class CustomRenditionProvider implements RenditionProvider { (1)

	@Override
	public String consumes() {
		return "my/type";
	}

	@Override
	public String[] produces() {
		return new String[] { "your/type" };
	}

	@Override
	public InputStream convert(InputStream fromInputSource, String toMimeType) {
}

...

@Configuration
@ComponentScan("my.custom.rendition.provider")         (3)
public static class ApplicationConfig {
}

  1. Implementation of RenditionProvider

  2. Marked as an @Service

  3. Ensure the service is scanned by Spring and offered as a bean