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Preface

Project metadata

1. Introduction

REST web services have become the number one means for application integration on the web. In its core, REST defines that a system consists of resources that clients interact with. These resources are often also implemented in a hypermedia driven way. Spring MVC offers a solid foundation to build theses kinds of services. But implementing even the simplest REST web services for a multi-domain object system can be quite tedious and result in a lot of boilerplate code.

Spring Content REST builds on top of Spring Content stores and automatically exports those as REST resources. It leverages REST to expose end-points for each content resource and it also optionally integrates with Spring Data REST’s hypermedia API to allow clients to find content resources that have been associated with Spring Data entities.

Spring Content REST officially supports:

2. Getting Started

2.1. Introduction

Spring Content REST is itself a Spring MVC application and is designed in such a way that it should integrate with your existing Spring MVC applications with very little effort.

2.2. Adding Spring Content REST to a Spring Boot project

The simplest way to get to started is if you are building a Spring Boot application. That’s because Spring Content REST has both a starter as well as auto-configuration.

Example 1. Spring Boot configuration with Gradle
dependencies {
    ...
    compile("com.github.paulcwarren:spring-content-rest-boot-starter:${version}")
	...
}
Example 2. Spring Boot configuration with Maven
 <dependencies>
	...
    <dependency>
      <groupId>com.github.paulcwarren</groupId>
      <artifactId>spring-content-rest-boot-starter</artifactId>
      <version>${version}</version>
    </dependency>
	...
  </dependencies>

When using Spring Boot, Spring Content REST gets configured automatically.

2.3. Adding Spring Content REST to a Gradle Project

To add Spring Content REST to a Gradle-based project, add the spring-content-rest artifact to your compile-time dependencies:

dependencies {
    ...
    compile("com.github.paulcwarren:spring-content-rest:${version}")
	...
}

2.4. Adding Spring Content REST to a Maven Project

To add Spring Content REST to a Maven-based project, add the spring-content-rest artifact to your compile-time dependencies:

 <dependencies>
	...
    <dependency>
      <groupId>com.github.paulcwarren</groupId>
      <artifactId>spring-content-rest</artifactId>
      <version>${version}</version>
    </dependency>
	...
  </dependencies>

2.5. Configuring Spring Content REST

To install Spring Content REST alongside your existing Spring MVC application, you need to include the appropriate MVC configuration. Spring Content REST configuration is defined in two classes called; RestConfiguration and HypermediaConfiguration and they can just be imported into your applications configuration.

Important
This step is unnecessary if you are using Spring Boot’s auto-configuration. Spring Boot will automatically enable Spring Content REST when you include com.github.paulcwarren:spring-content-rest-boot-starter and your app is flagged as a @SpringBootApplication.

Make sure you also configure Spring Content stores for the store you wish to use. For details on that, please consult the reference documentation for the corresponding Spring Content module.

3. Store Resources

3.1. Fundamentals

The core functionality of Spring Content REST, enabled through @Import(RestConfiguration.class), is to export resources for Spring Content stores. This is often closely related to Spring Data repositories.

The following describes typical store scenarios and how they are exported with Spring Content REST.

3.1.1. Resources

Spring Content Stores manage Spring Resources that, when exported using Spring Content REST, are accessible by REST endpoint.

Consider the following Store interface:

  public interface DvdStore extends Store<String> {}

In this example, the Store’s Resources are exported to the URI /dvds. The path is derived from the uncapitalized, pluralized, simple class name of the interface. When interacting with this endpoint any additional path is deemed to be the Resource’s location and will be used to fetch the Resource using the Store’s getResource method. For example, a GET request to /dvds/comedy/monty_pythons_flying_circus.mp4 will fetch from the DvdStore (/dvds), the Resource /comedy/monty_pythons_flying_circus.mp4.

3.1.2. Entity Resources

Entity Resources are Spring Resource associated with Spring Data Entities.

Assume the following Entity class, Repository and Store interfaces:

  @Entity
  public class Dvd {
  	@Id
  	private Long id;

    @ContentId
    private UUID contentId;

  	@ContentLength
  	private Long contentLength;

  	@MimeType
  	private String mimeType;

  	// getters and setters
  }

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

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

In this example a single Spring Resource (the DVD’s video stream) is associated with a Dvd Entity by annotating additional fields on the Entity using the @ContentId, @ContentLength and @MimeType annotations. In this example Spring Data REST exports a collection resource to /dvds. The path is derived from the uncapitalized, pluralized, simple class name of the domain class. Item resources are also exported to the URI /dvds/{id}. The HTTP methods used to request this endpoint map onto the methods of CrudRepository.

Similarly, Spring Content REST also exports any associated Spring Resources to the URI /dvds/{id}. In this case the HTTP methods map onto the methods of ContentStore as follows:-

  • GET → getContent

  • POST/PUT → setContent

  • DELETE → unsetContent

3.1.3. Property Resources

Property Resources are associated with the properties of Spring Data Entities, that themselves maybe Spring Data Entities. This allows many Resources to be associated with a single Entity.

Consider the following Entity model, with Repository and Store interfaces:

@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> {}

In this example separate Resources are associated with the image and stream properties of the Dvd Entity.

When using JPA and its relational characteristics these associations are typically (but not always) also Entity associations as well, as shown here. However when using NoSQL databases like MongoDB that are capable of storing hierarchical data they are true property associations.

As before, Spring Data REST will export an item resource under the URI /dvds/{id}. However, this time Spring Content REST will export Property Resources to the URI /dvds/{id}/image/{contentId} and /dvds/{id}/stream/{contentId} managed by the respective Store. A property can be set by POSTing to /dvds/{id}/image (or /dvds/{id}/stream).

Note
as these properties are both single values these Resources are also available under the simplified URI /dvds/{id}/image and /dvds/{id}/stream where the {contentId} is omitted for convenience.

3.1.4. Property Collection Resources

Property Resources can also target Collections.

Consider the following example:-

@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> {}

In this example many Resources can be associated with the chapters property of the Dvd Entity.

As with Property Resources, Property Collection Resources are also exported to the URI /dvds/{id}/chapters. However, in this case, POSTing to /dvds/{id}/chapters always appends a new Resource to the 'Chapters' Collection. This Resource supports both POST and PUT HTTP methods.

Exported content stores may be marked as Searchable. Assuming the following content store interface:

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

When the store is exported, Spring Content REST exposes a fulltext query resource for the Searchable.search methods. These resources are exported to the URI /dvds/searchContent. Method parameters can be supplied as query parameters:

  curl -H 'Accept: application/hal+json'  http://localhost:8080/searchContent?queryString=foo

3.1.6. Default status codes

For the content resources exposed, we use a set of default status codes:

  • 200 OK - for plain GET requests and POST and PUT requests that overwrite existing content resources

  • 201 Created - for POST and PUT requests that create new content resources

  • 204 No Content - for DELETE requests

  • 206 Partial Content - for range GET requests

3.1.7. Resource Discoverability

A core principle of HATEOAS is that Resources should be discoverable through the publication of links that point to the available resources. There are a few competing de-facto standards specifying how to represent links in JSON. By default, Spring Data REST uses HAL to render responses. HAL defines links to be contained in a property of the returned document.

Resource discovery starts at the top level of the application. By issuing a request to the root URL under which the Spring Data REST application is deployed, the client can extract a set of links from the returned JSON object that represent the next level of resources that are available to the client.

When enabled through @Import(HypermediaConfiguration.class) Spring Content REST will inject Store, Entity and Property Resources links for both into the HAL responses created by Spring Data REST.

3.2. The Store Resource

Spring Content REST exports Store Resources to /{store}/**. The resource path and linkrel can be customized using the @StoreRestResource annotation on the Store interface.

3.2.1. Supported HTTP Methods

Store Resources support GET, PUT, POST, and DELETE. All other HTTP methods will cause a 405 Method Not Allowed.

GET

Returns the Resource’s content

Supported media types

All content types except application/json

PUT/POST

Sets the Resources’s content

Supported media types

All content types except application/json

DELETE

Removes the Resource’s content

Supported media types

All content types except application/json

3.3. The Entity Resource

Spring Content REST exports Entity Resources to /{store}/{id}. The resource path can be customized using the @StoreRestResource annotation on the Store interface.

3.3.1. Supported HTTP Methods

Entity Resources support GET, PUT, POST, and DELETE. All other HTTP methods will cause a 405 Method Not Allowed.

GET

Returns the Resource’s content

Supported media types

All content types except application/json

PUT/POST

Sets the Resources’s content

Supported media types

All content types except application/json

DELETE

Removes the Resource’s content

Supported media types

All content types except application/json

3.4. The Property Resource

Spring Content REST exports Property Resources to /{store}/{id}/{property} and /{store}/{id}/{property}/{contentId}. The resource path can be customized using the @StoreRestResource annotation on the Store interface.

3.4.1. Supported HTTP Methods

Property Resources support GET, PUT, POST, and DELETE. All other HTTP methods will cause a 405 Method Not Allowed.

GET

Returns the Resource’s content

Supported media types

All content types except application/json

PUT/POST

Sets the Resources’s content

Supported media types

All content types except application/json

DELETE

Removes the Resource’s content

3.5. The Collection Property Resource

Spring Content REST exports Property Collection Resources to /{store}/{id}/{property}. The resource path can be customized using the @StoreRestResource annotation on the Store interface.

3.5.1. Supported HTTP Methods

Content collection resources support PUT and POST.

PUT/POST

Appends new content to the collection of Resources

Supported media types

All content types except application/json

4. Repository Resources (Spring Data REST Extensions)

4.1.1. The SearchContent Resource

When a Store extending Searchable is exported, a searchContent endpoint will be available at the /{store}/searchContent URI.

  curl -H 'Accept: application/hal+json'  http://localhost:8080/searchContent?queryString=foo
Supported HTTP Methods

As the SearchContent resource is read-only it supports GET only. All other HTTP methods will cause a 405 Method Not Allowed.

Supported media types
  • application/hal+json

  • application/json.

4.2. Locking and Versioning

4.2.1. The Lock Resource

When a repository extending LockingAndVersioningRepository is exported a lock endpoint will be available at the /{repository}/{id}/lock URI.

  curl -X PUT http://localhost:8080/docs/1234/lock
  curl -X DELETE http://localhost:8080/docs/1234/lock
Supported HTTP Methods

The Lock resource supports PUT and DELETE. All other HTTP methods will cause a 405 Method Not Allowed.

PUT

Acquires a pessimistic lock on the resource.

DELETE

If held, releases the pessimistic lock on the resource.

Supported media types

Not applicable.

4.2.2. The Version Resource

When a repository extending LockingAndVersioningRepository is exported a version endpoint will be available at the /{repository}/{id}/version URI.

  curl -X PUT http://localhost:8080/docs/1234/version -d '{"number": "1.1", "label": "a minor change"}'
Supported HTTP Methods

The version resource supports PUT. All other HTTP methods will cause a 405 Method Not Allowed.

PUT

Creates a new version of the entity.

Supported media types

application/json

4.2.3. The FindAllVersionsLatest Resource

When a repository extending LockingAndVersioningRepository is exported a findAllVersionsLatest endpoint will be available at the /{repository}/findAllVersionsLatest URI.

  curl -X GET http://localhost:8080/docs/findAllVersionsLatest
Supported HTTP Methods

The version resource supports GET. All other HTTP methods will cause a 405 Method Not Allowed.

GET

Returns the latest version of all entities.

Supported media types

Not applicable.

4.2.4. The FindAllVersions Resource

When a repository extending LockingAndVersioningRepository is exported a findAllLatestVersions endpoint will be available at the /{repository}/{id}/findAllVersions URI.

  curl -X GET http://localhost:8080/docs/1234/findAllVersions
Supported HTTP Methods

The version resource supports GET. All other HTTP methods will cause a 405 Method Not Allowed.

GET

Returns all versions of the given entity.

Supported media types

Not applicable.

5. Customizing Store Resources

5.1. Configuring CORS

For security reasons, browsers prohibit AJAX calls to resources residing outside the current origin. When working with client-side HTTP requests issued by a browser you may want to enable specific HTTP resources to be accessible.

Spring Data Content supports Cross-Origin Resource Sharing (CORS) through Spring’s CORS support.

5.1.1. Store Interface CORS Configuration

You can add a @CrossOrigin annotation to your store interfaces to enable CORS for the whole store. By default @CrossOrigin allows all origins and HTTP methods:

@CrossOrigin
interface DvdStore extends ContentStore<Dvd, UUID> {}

In the above example CORS support is enabled for the whole DvdStore. @CrossOrigin also provides attributes to perform more granular configuration.

@CrossOrigin(origins = "http://mydomain.com",
  methods = { RequestMethod.GET, RequestMethod.POST, RequestMethod.DELETE },
  maxAge = 3600)
interface DvdStore extends ContentStore<Dvd, UUID> {}

This example enables CORS support for the whole DvdStore providing one origin, restricted to GET, POST and DELETE methods with a max age of 3600 seconds.

5.1.2. Global CORS Configuration

In addition to fine-grained, annotation-based configuration, you probably want to define some global CORS configuration as well. This is similar to Spring Web MVC’S CORS configuration but can be declared within Spring Content REST and combined with fine-grained @CrossOrigin configuration. By default, all origins and GET, HEAD, and POST methods are allowed.

The following example sets up the same CORS configuration but as a global configuration:

@Configuration
public class SpringContentRestCustomization {

	@Bean
	private ContentRestConfigurer contentRestConfigurer() {

		return new ContentRestConfigurer() {
			@Override
			public void configure(RestConfiguration config) {
				config.getCorsRegistry().addMapping("/dvds/**")
						.allowedMethods("GET", "POST", "DELETE")
						.allowedOrigins("http://mydomain.com")
						.maxAge(3600);
			}
		};
	}
}

5.2. Changing the Base URI

By default, Spring Content REST serves up REST resources at the root URI, '/'.

With Spring Boot 1.2 and later versions, you can change the base URI by setting a single property in application.properties, as follows:

spring.content.rest.baseUri=/api

Or if you are not using Spring Boot, you can do the following:

@Configuration
class CustomContentRestMvcConfiguration {

  @Bean
  public ContentRestConfigurer contentRestConfigurer() {

    return new ContentRestConfigurer() {

      @Override
      public void configure(RestConfiguration config) {
        config.setBaseUri(URI.create("/contentApi"));
      }
    };
  }
}

For each exported Spring Resource, Spring Content REST will generate a suitable linkrel.

However, it can sometimes be useful to control this yourself.

Given the following example:

  @Entity
  public class Dvd {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ContentId
    private UUID contentId;

    @ContentLength
    private Long contentLength;

    @MimeType
    private String mimeType;

    // getters and setters
  }

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

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

Spring Content REST will export the Spring Resource to the following linkrel:

  "_links" : {
    "self" : {
      ...
    },
    "dvd" : {
      ...
    },
    "dvds" : {
      "href" : "http://localhost:8080/dvds/1"
    }
  }

Specifying a linkRel on the StoreRestResource, as follows:

  @StoreRestResource(linkRel="content")
  public interface DvdStore extends ContentStore<Dvd, UUID> {}

will result in the following linkrel instead:

 "_links" : {
    "self" : {
      ...
    },
    "dvd" : {
      ...
    },
    "content" : {
      "href" : "http://localhost:8080/dvds/1"
    }
  }

By default, and where possible, Spring Content REST exports Spring Resources to shortened link URIs. These will often match the Spring Data Rest Entity URI.

Given the following example:

  @Entity
  public class Dvd {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ContentId
    private UUID contentId;

    @ContentLength
    private Long contentLength;

    @MimeType
    private String mimeType;

    // getters and setters
  }

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

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

As there is only a single associated Spring Resource, Spring Content REST will generate the following URI:

  "_links" : {
    "self" : {
      ...
    },
    "dvd" : {
      ...
    },
    "dvds" : {
      "href" : "http://localhost:8080/dvds/1"
    }
  }

To generate fully qualified link URIs set the following property:

spring.content.rest.fullyQualifiedLinks=true

Or if you are not using Spring Boot, you can do the following:

@Configuration
class CustomContentRestMvcConfiguration {

  @Bean
  public ContentRestConfigurer contentRestConfigurer() {

    return new ContentRestConfigurer() {

      @Override
      public void configure(RestConfiguration config) {
        config.setFullyQualifiedLinks(true);
      }
    };
  }
}

Spring Content REST will now generate links as follows:

  "_links" : {
    "self" : {
      ...
    },
    "dvd" : {
      ...
    },
    "content" : {
      "href" : "http://localhost:8080/dvds/1/content"
    }
  }

where content is the extracted property name taken from the field contentId.

5.5. Store Resolver

Every REST request must map to one store and one store only. However, it is entirely possible to define an application with multiple stores that make this impossible.

For these situations you need to provide a StoreResolver that, based on runtime context, can resolve these conflicts.

Example 3. Configuring a StoreResolver
public interface S3ExampleStore extends S3ContentStore<Example, UUID>{}
public interface FSExampleStore extends FilesystemContentStore<Example, UUID>{}     (1)

@Configuration
@EnableS3Stores
@EnableFilesystemStores
public static class ApplicationConfig {

    @Bean
    public ContentRestConfigurer contentRestConfigurer() {
        return new ContentRestConfigurer() {
            @Override
            public void configure(RestConfiguration config) {
                config.addStoreResolver("examples", new StoreResolver() {           (2)
                    @Override
                    public StoreInfo resolve(StoreInfo... stores) {
                        /* your resolver implementation */
                    }
                });
            }
        };
    }
}
  1. Both stores are typed to the domain type Example and will therefore be exported to the URI /examples

  2. Store resolver resolves requests to /examples/…​ to either S3ExamplesStore or FSExampleStore, depending on request context.

5.6. Put/Post Content Handling

A ContentStore provides two methods for setting content. Spring Content REST prefers to use setContent(S entity, InputStream) over setContent(S entity, Resource) so that content is streamed through the application. This is usually the best approach.

However, under some circumstances this can be inconvenient when event handlers and store customizations must handle the content as it moves through the application. This also becomes inefficient when the content is large and the content needs to be processed several times.

For these situations, it is possible to configure Spring Content REST to call setContent(S entity, Resource) as follows:

Example 4. Configuring PUT/POST Handling
public interface ExampleStore extends ContentStore<Example, UUID>{}

@Configuration
public static class ApplicationConfig {

   @Bean
   public ContentRestConfigurer configurer() {
       return new ContentRestConfigurer() {
           @Override
           public void configure(RestConfiguration config) {
               config.forDomainType(Example.class).putAndPostPreferResource();
           }
       };
   }
}
Note
if preferred, it is also possible to configure your ContentStore to hide the setContent(S entity, InputStream) method by annotating this method with the RestResource(export=false) annotation.

When configured this way, Spring Content REST will create a file backed Resource allowing event handlers and store customizations to use File, RandomAccessFile and Channel Java io/nio APIs to process the content stream.

If you would like to defer until runtime so that a decision can be based on the request, you can instead provide a Resource<Method, HttpHeaders>, as follows:

Example 5. Deferring PUT/POST Handling until runtime
public interface ExampleStore extends ContentStore<Example, UUID>{}

@Configuration
public static class ApplicationConfig {

   @Bean
   public ContentRestConfigurer configurer() {
       return new ContentRestConfigurer() {
           @Override
           public void configure(RestConfiguration config) {

               config.forDomainType(TestEntity.class).setSetContentResolver(new Resolver<Method, HttpHeaders>(){

                @Override
                public boolean resolve(Method method, HttpHeaders context) {

                    return // your logic here
               }});
           }
       };
   }
}