How to simply enable HAL+JSON object mapping with Spring Restemplate - spring-data-rest

Question

I have been pulling my hair out trying to figure out how to simply enable this sort of functionality in my client in response to a HAL+JSON request. If I have the specific resource I can get the properties to bind but really would like the hrefs in an easy to use format so I can lazy fetch them.
Organization[] orgs = restTemplate.getForObject("http://myservice/organizations",Organizations[].class);
or
Organization org = restTemplate.getForObject("http://myservice/organizations/1",Organization.class);
Given the following HAL and entities:
{
"_embedded": {
"af:organizations": [
{
"name": "First Company",
"description": "Some company",
"_links": {
"self": {
"href": "http://localhost:8080/hal/organizations/1"
},
"af:workers": {
"href": "http://localhost:8080/hal/organizations/1/workers",
"title": "Cancel an order"
}
}
},
{
"name": "Second Company",
"description": "Someplace we all used to work",
"_links": {
"self": {
"href": "http://localhost:8080/hal/organizations/2"
},
"af:workers": {
"href": "http://localhost:8080/hal/organizations/2/workers",
"title": "All the little ants on your farm"
}
}
}
]
},
"_links": {
"self": {
"href": "http://localhost:8080/hal/organizations"
},
"profile": {
"href": "http://localhost:8080/hal/profile/organizations"
},
"curies": [
{
"href": "/custom/docs/{rel}.txt",
"name": "af",
"templated": true
}
]
}
}
entity
import lombok.AllArgsConstructor;
import lombok.EqualsAndHashCode;
import lombok.Getter;
import lombok.NoArgsConstructor;
import java.util.List;
#Getter
#NoArgsConstructor
#EqualsAndHashCode
#AllArgsConstructor
public class Organization {
private String name;
private String description;
#JsonProperty("_links")
private Map<String, Link> links;
}
Configuration (which is my 3rd attempt. It's just my current one)
#Configuration
#EnablePluginRegistries(RelProvider.class)
#PropertySource("classpath:ant-farm-client.properties")
public class AntFarmClientConfig {
#Value("${server.url}")
private String base;
private static final boolean EVO_PRESENT =
ClassUtils.isPresent("org.atteo.evo.inflector.English", null);
#Autowired
private PluginRegistry<RelProvider, Class<?>> relProviderRegistry;
#Bean
public ObjectMapper jacksonObjectMapper() {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
return objectMapper;
}
#Bean
public MappingJackson2HttpMessageConverter jsonConverter() {
MappingJackson2HttpMessageConverter jacksonConverter = new
MappingJackson2HttpMessageConverter();
jacksonConverter.setSupportedMediaTypes(Arrays.asList(MediaType.valueOf("application/json")));
jacksonConverter.setObjectMapper(jacksonObjectMapper());
return jacksonConverter;
}
#Bean
public CurieProvider curieProvider() {
return new DefaultCurieProvider("af", new UriTemplate("http://schema.org/{rel}"));
}
#Bean
MessageSourceAccessor accessor(ApplicationContext context) {
return new MessageSourceAccessor(context);
}
#Bean
public RestOperations template(ObjectMapper mapper,MappingJackson2HttpMessageConverter halConverter ) {
RestTemplate restTemplate = new RestTemplate();
DefaultUriTemplateHandler handler = new DefaultUriTemplateHandler();
handler.setBaseUrl(base);
restTemplate.setUriTemplateHandler(handler);
restTemplate.getMessageConverters().add(halConverter);
return restTemplate;
}
#Bean
public MappingJackson2HttpMessageConverter halConverter(MessageSourceAccessor accessor) {
CurieProvider curieProvider = curieProvider();
RelProvider relProvider = new DelegatingRelProvider(relProviderRegistry);
ObjectMapper halObjectMapper = new ObjectMapper();
halObjectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
halObjectMapper.registerModule(new Jackson2HalModule());
halObjectMapper.setHandlerInstantiator(new
Jackson2HalModule.HalHandlerInstantiator(relProvider, curieProvider,accessor));
MappingJackson2HttpMessageConverter halConverter = new MappingJackson2HttpMessageConverter();
halConverter.setSupportedMediaTypes(Arrays.asList(MediaTypes.HAL_JSON));
halConverter.setObjectMapper(halObjectMapper);
return halConverter;
}
#Bean
RelProvider defaultRelProvider() {
return EVO_PRESENT ? new EvoInflectorRelProvider() : new DefaultRelProvider();
}
#Bean
RelProvider annotationRelProvider() {
return new AnnotationRelProvider();
}

Answer 1

I would try to get a Resources<Resource<Organization>> out of the RestTemplate. The outer Resources would contain the global links and each Resource in the content contains the item links then.
I would not create my own ObjectMapper - spring hateoas provides one. It is just important that your RestTemplate has the HttpMessageConverter in place that can convert application/hal+json.
This article shows an example for doing this https://dzone.com/articles/spring-resttemplate-linked
Currently I cannot try this myself so I can just provide you with these untested thoughts.