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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.from("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.

1.4. 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);

1.4.1. 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);

1.5. 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.

1.5.1. 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.

1.6. 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

1.6.1. 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 AbstractStoreEventListener
public class ExampleEventListener extends AbstractStoreEventListener {

	@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.

1.6.2. 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();
	}
}

1.7. 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.

1.8. 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.

1.9. Error Translation

When using Stores, you must decide how to handle the storage technology’s native exception classes. Typically, storage layers throw runtime exceptions and do not have to be declared or caught. You may also have to deal with IllegalArgumentException and IllegalStateException. This means that callers can only treat exceptions as being generally fatal, unless they want to depend on the storage technology’s own exception structure. This trade-off might be acceptable to applications that are strongly aligned to a particular storage or do not need any special exception treatment (or both). However, Spring Content lets exception translation be applied transparently through the @Store annotations. The following examples show how to contribute a bean that implements StoreExceptionTranslator that translates RuntimeException’s to StoreAccessExceptions:

Example 16. StoreExceptionTranslator interface
@Configuration
public class Config {

    @Bean
    public StoreExceptionTranslator translator() {
        return new StoreExceptionTranslator() {
            @Override
            public StoreAccessException translate(RuntimeException re) {
                ...
            }
        };
    }
	InputStream getRendition(E entity, String mimeType);
}

1.10. 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

2. Filesystem Content Stores

2.1. Maven Central Coordinates

The maven coordinates for this Spring Content library are:

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

2.2. Annotation-based Configuration

Spring Content Filesystem Stores are enabled with the following Java Config.

Example 17. Spring Content Filesystem Stores using Java Config
@Configuration
@EnableFilesystemStores
public static class ApplicationConfig {

    @Bean
    File filesystemRoot() {
        try {
            return Files.createTempDirectory("").toFile();
        } catch (IOException ioe) {}
        return null;
    }

    @Bean
    FileSystemResourceLoader fileSystemResourceLoader() {
        return new FileSystemResourceLoader(filesystemRoot().getAbsolutePath());
    }

}

By default content will be stored in a randomly chosen (at application startup) folder

2.3. Spring Boot Configuration

When using spring-content-fs-boot-starter (or content-fs-spring-boot-starter) the root for all file system stores will be a randomly chosen folder (at application start-up) under java.io.tmdir.

The following configuration properties (prefix spring.content.fs) are supported.

Property Description

filesystemRoot

The root location where file system stores place their content (defaults to java.io.tmpdir/<random>/).

2.4. Accessing Storage

2.4.1. Signature Types

Filesystem Storage supports the following signature types:

  • org.springframework.content.fs.store.FilesystemStore

  • org.springframework.content.fs.store.FilesystemAssociativeStore

  • org.springframework.content.fs.store.FilesystemContentStore

The module id for the spring.content.storage.type.default property is fs.

2.4.2. Loading Spring Resources from a Store or AssociativeStore

Resources returned by Filesystem Storage are standard Spring Resources implementing the following interfaces:

  • org.springframework.core.io.Resource

  • org.springframework.core.io.WriteableResource

  • org.springframework.content.commons.io.DeleteableResoure

When a Resource is loaded from the Store the following rules are used to determine the resource’s location.

For a Store, when a Resource is loaded using a call to getResource(ID location).

  • if the store’s ID is typed to a String this will be used as-is as the resource’s location

  • otherwise, if a registered Spring Converter exists that converts the Store’s ID type to a String this will be used to convert the value to a String location

For an AssociativeStore (or indirectly a ContentStore), when a Resource is loaded from a call to getResource(S entity):

  • if a registered Spring Converter exists that converts the the Store’s entity (S) type to a String this will be used convert the value to a String location.

  • otherwise, the Entity’s @ContentId field will be used as the resource’s location

See Configuring a Spring Converter for more information on how to register a converter.

2.4.3. Setting Content

Storing content is achieved using the ContentStore.setContent(T entity, PropertyPath path, InputStream content, SetContentParams params) method.

The PropertyPath will be used to resolve the content property to update.

If content has not yet been stored with this entity and an Id has not been assigned, one will be generated based in java.util.UUID.

The @ContentId and @ContentLength annotations will be updated on entity.

If content has previously been stored it will be overwritten also updating the @ContentLength attribute, if present. However, using ContentDisposition.Create on the SetContentParams a new Id will be assigned and content stored, leaving the existing content in place and orphaned.

2.4.4. Getting Content

Content can be accessed using the ContentStore.getContent(T entity, PropertyPath path) method.

2.4.5. Unsetting Content

Content can be removed using the ContentStore.unsetContent(T entity, PropertyPath path, UnsetContentParams params) method. Using ContentDisposition.Keep on UnsetContentParams will leave the content in storage and orphaned.

2.4.6. Storage Customization

By default, the Filesystem Store Module will store all content at the root of the backing store. Usually, this is sufficient.

However, for the cases where you need more control over the content in the backing store, the Module provides a placement service. This service can be configured through a standard Spring converter in a couple of different ways, depending on requirements.

Assume you have a Document entity like this:

@Entity
@Data
public class Document {

    @Id
    @GeneratedValue(strategy=AUTO)
    private Long id;

    @ContentId
    private UUID contentId;

    @ContentLength
    private Long contentLength;

    @MimeType
    private String mimeType;

    private String contentPath;
}

The first option is a converter that converts from the @ContentId type, in this case UUID, to String.

Example 18. Spring Content Filesystem Stores customizing storage customization by @ContentId type
@Configuration
public class FilesystemStoreConfiguration  {

   	public Converter<UUID,String> converter() {
		return new FilesystemStoreConverter<UUID,String>() {

			@Override
			public String convert(UUID source) {
				return String.format("/%s", source.toString().replaceAll("-", "/"));
			}
		};
	}

	@Bean
	public FilesystemStoreConfigurer configurer() {
		return new FilesystemStoreConfigurer() {

			@Override
			public void configureFilesystemStoreConverters(ConverterRegistry registry) {
				registry.addConverter(converter());
			}
		};
	}
}

This example uses a converter to generate a random location on disk based on the contentId

For example, a Document with a contentId of ec39f99b-5de3-4dc5-9753-a97c26f809c2 would be stored in the backing store at /ec39f99b/5de3/4dc5/9753/a97c26f809c2.

The second option is a converter that converts from the Entity type to String.

Example 19. Spring Content Filesystem Stores customizing storage customization by Entity type
@Configuration
public static class StoreConfig {
    @Bean
    public FilesystemStoreConfigurer configurer() {
        return new FilesystemStoreConfigurer() {

            @Override
            public void configureFilesystemStoreConverters(ConverterRegistry registry) {
                registry.addConverter(new Converter<Document, String>() {

                    @Override
                    public String convert(Document document) {
                        return document.getContentPath();
                    }
                });
            }
        };
    }

	@Bean
	public FilesystemStoreConfigurer configurer() {
		return new FilesystemStoreConfigurer() {

			@Override
			public void configureFilesystemStoreConverters(ConverterRegistry registry) {
				registry.addConverter(converter());
			}
		};
	}
}

This example allows the application to control the location in the backing store with a field on the entity.

For example, if you created a Document and set its contentPath to /path/to/my-file the content will be stored in the backing store at /path/to/my-file.

3.1. Overview

When enabled the Solr integration will forward all content to Solr for fulltext indexing which can then be searched by adding the optional Searchable<CID> interface to the Content Repositories.

3.2. Dependencies

Add the solrj to the classpath.

	<dependency>
		<groupId>org.apache.solr</groupId>
		<artifactId>solr-solrj</artifactId>
		<version>5.5.3</version>			(1)
		<exclusions>
			<exclusion>
				<groupId>org.codehaus.woodstox</groupId>
				<artifactId>wstx-asl</artifactId>
			</exclusion>
			<exclusion>
				<artifactId>log4j</artifactId>
				<groupId>log4j</groupId>
			</exclusion>
		</exclusions>
	</dependency>

  1. If using Spring Boot the version may be omitted

3.3. Enabling

  • Specify the @EnableFullTextSolrIndexing annotation to your @Configuration Spring Application block.

  • Ensure a (SolrJ) SolrClient @Bean is instantiated somewhere within your @Configuration Spring Application block.

3.4. Configuring

By default when the Solr module is enabled Spring-Content looks for a http://localhost:8983/solr/solr solr server with no username or password.

To change this behavior the following variables need to be set via the Externalized Configuration method.

Property Description

solr.url

Url of the Solr host (including port and core)

solr.username

Solr user

solr.password

Solr user’s password