spring-data-rest/doc/changing_json.md

Customizing the JSON output

Sometimes in your application you need to provide links to other resources from a particular entity. For example, a Customer response might be enriched with links to a current shopping cart, or links to manage resources related to that entity. Spring Data REST provides integration with Spring HATEOAS and provides an extension hook for users to alter the representation of resources going out to the client.

The ResourceProcessor interface

Spring HATEOAS defines a ResourceProcessor<?> interface for processing entities. All beans of type ResourceProcessor<Resource<T>> will be automatically picked up by the Spring Data REST exporter and triggered when serializing an entity of type T. For example, to define a processor for a Person entity, add a @Bean to your ApplicationContext like the following (which is taken from the Spring Data REST tests):

	@Bean public ResourceProcessor<Resource<Person>> personProcessor() {
		return new ResourceProcessor<Resource<Person>>() {
			@Override public Resource<Person> process(Resource<Person> resource) {
				resource.add(new Link("http://localhost:8080/people", "added-link"));
				return resource;
			}
		};
	}

Adding Links

It's possible to add links to the default representation of an entity by simply calling resource.add(Link) like the example above. Any links you add to the Resource will be added to the final output.

Customizing the representation

The Spring Data REST exporter executes any discovered ResourceProcessors before it creates the output representation. It does this by registering a Converter<Entity, Resource> instance with an internal ConversionService. This is the component responsible for creating the links to referenced entities (e.g. those objects under the "links" property in the object's JSON representation). It takes an @Entity and iterates over its properties, creating links for those properties that are managed by a Repository and copying across any embedded or simple properties.

If your project needs to have output in a different format, however, it's possible to completely replace the default outgoing JSON representation with your own. If you register your own ConversionService in the ApplicationContext and register your own Converter<Person, Resource>, then you can return a Resource implementation of your choosing.