Return IDs in JSON response from Spring Data REST

The accepted answer overrides a deprecated method. Here's the updated version:

@Component
public class RestConfig implements RepositoryRestConfigurer {

    @Override
    public void configureRepositoryRestConfiguration(RepositoryRestConfiguration config, CorsRegistry cors) {
        config.exposeIdsFor(Book.class);
    }
}

An alternative approach is to implement RepositoryRestConfigurer in your @SpringBootApplication annotated class:

@SpringBootApplication
public class MyApplication implements RepositoryRestConfigurer {

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

    @Override
    public void configureRepositoryRestConfiguration(RepositoryRestConfiguration config, CorsRegistry cors) {
        config.exposeIdsFor(Book.class);
    }

}

Spring Data Rest hides the ID by default, in order to have it in the JSON you have to manually configure that for your entity. Depending on your spring version you can either provide your own configuration (old):

@Configuration
public class ExposeEntityIdRestConfiguration extends RepositoryRestMvcConfiguration {

    @Override
    protected void configureRepositoryRestConfiguration(RepositoryRestConfiguration config) {
        config.exposeIdsFor(Book.class);
    }
}

...or register a RepositoryRestConfigurer (current):

@Component
public class ExposeEntityIdRestMvcConfiguration extends RepositoryRestConfigurerAdapter {

  @Override
  public void configureRepositoryRestConfiguration(RepositoryRestConfiguration config) {
    config.exposeIdsFor(Book.class);
  }
}

See the Spring Data Rest documentation for more details.