Send POST and PUT through RestTemplate to a Spring Data Rest Api - json

Question

I've been developing a cloud app to mess a little with Spring Cloud and such. Now I'm stuck trying to send a POST or a PUT request to a Spring Data Rest backend using the RestTemplate API but everything I tried ends with an error: HttpMessageNotReadableException: Cannot deserialize instance of java.lang.String out of START_OBJECT token, HttpMessageNotReadableException: Could not read document: Can not deserialize instance of java.lang.String out of START_ARRAY token, ...from request with content type of application/xml;charset=UTF-8!, Error 400 null... you name it. After researching I discovered that it actually is quite hard to consume HAL JSON with RestTemplate (level 3 JSON hypermedia if I recall correctly) but I want to know if it is possible.
I'd like to see some working (detailed if possible) examples of a RestTemplate sending POST and PUT to a Spring Data Rest backend.
Edit: I tried postForEntity, postForLocation, exchange and it just ended in different kinds of errors. Those are some snippets I tried (there're more, it's just that I dispose them).
My entity:
#Entity
public class Account implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
#NotNull
#NotEmpty
private String username;
#NotNull
#NotEmpty
private String authorities;
#NotNull
#NotEmpty
private String password;
//Constructor, getter and setter
Some restTemplate attemps:
public Account create(Account account) {
//Doesnt work :S
MultiValueMap<String, String> map = new LinkedMultiValueMap<String, String>();
map.add("name", account.getName());
map.add("username", account.getUsername());
map.add("password", account.getPassword());
map.add("authorities", account.getAuthorities());
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);
final HttpEntity<MultiValueMap<String, String>> entity = new HttpEntity<MultiValueMap<String, String>>(map,
headers);
return restTemplate.exchange(serviceUrl + "/accounts", HttpMethod.POST, entity, Account.class).getBody();
}
//Also tried with a AccountResource which extends from ResourceSupport and doesn't work either. This one gives me a error saying it cannot deserialize Account["name"].
Also tried like this and got an error about header being application/xml: RestTemplate POSTing entity with associations to Spring Data REST server
The other ones just repeat one of those errors.

Answer 1

You need to configure your RestTemplate so it can consume the application/hal+json content type.
It has already been addressed in some other posts, such as this one or that one, and on a bunch of blog posts, such as here.
The following solution works for a Spring Boot project:
First, configure your RestTemplate using a bean:
// other import directives omitted for the sake of brevity
import static org.springframework.hateoas.MediaTypes.HAL_JSON;
#Configuration
public class RestTemplateConfiguration {
#Autowired
private ObjectMapper objectMapper;
/**
*
* #return a {#link RestTemplate} with a HAL converter
*/
#Bean
public RestTemplate restTemplate() {
// converter
MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
converter.setSupportedMediaTypes(Arrays.asList(HAL_JSON));
converter.setObjectMapper(objectMapper);
RestTemplate restTemplate = new RestTemplate(Collections.singletonList(converter));
return restTemplate;
}
}
Then, let Spring inject the RestTemplate where you need to consume the REST backend, and use one of the many variants of RestTemplate#exchange:
#Autowired
public RestTemplate restTemplate;
...
// for a single ressource
// GET
Account newAccount = restTemplate.getForObject(url, Account.class);
// POST
Account newAccount = restTemplate.exchange(serviceUrl + "/accounts", HttpMethod.POST, entity, Account.class).getBody();
// or any of the specialized POST methods...
Account newAccount = restTemplate.postForObject(serviceUrl + "/accounts", entity, Account.class);
For a collection, you will manipulate a PagedResources
// for a collection
ParameterizedTypeReference<PagedResources<Account>> responseType =
new ParameterizedTypeReference<PagedResources<Account>>() {};
// GET
PagedResources<Account> accounts =
restTemplate.exchange(url, HttpMethod.GET, null, responseType).getBody();
//