Returning HAL json from HttpServletResponse - spring

Question

I am trying to return a response body in my "successfullAuthentication" method in "UsernamePasswordAuthenticationFilter" using HATEOAS, but is returning the links in this format:
"links": [
{
"rel": "self",
"href": "http://localhost:8080/api/users/5c55ee26911e9f04acb77c91",
"hreflang": null,
"media": null,
"title": null,
"type": null,
"deprecation": null
},
I would like it to return HAL json format so it would look like this:
"_links": {
"self": {
"href": "http://localhost:8080/api/users/5c55ee26911e9f04acb77c91"
},
I have this in my method (response is HttpServletResponse):
User user = userService.findById(authResult.getName());
String json = Jackson.toJsonString(userResourceAssembler.toResource(user));
response.setContentType("application/hal+json");
response.setCharacterEncoding("UTF-8");
response.addHeader(jwtConfig.getHeader(), jwtConfig.getPrefix() + token);
response.getWriter().write(json);
I also have this in my WebConfig: #EnableHypermediaSupport(type = { EnableHypermediaSupport.HypermediaType.HAL })
Does anyone know why this is happening?

Answer 1

I found the answer in this github issue: https://github.com/spring-projects/spring-hateoas/issues/270#issuecomment-145606558
Basically:
private String convertToHalString(ResourceSupport resource) {
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new Jackson2HalModule());
mapper.setHandlerInstantiator(new Jackson2HalModule.HalHandlerInstantiator(
new EvoInflectorRelProvider(), null, null));
String resourceString = null;
try {
resourceString = mapper.writeValueAsString(resource);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
return resourceString;
}

Answer 2

Try to extend all model classes- to add HATEOAS links –
with org.springframework.hateoas.ResourceSupport class
Presuming you have respective URI's in controller class
Link link = ControllerLinkBuilder
.linkTo(UserController.class)
.slash(user.getXXX())
.withSelfRel();
//for single resource
user.add(link);
Link userLink = ControllerLinkBuilder
.linkTo(ControllerLinkBuilder
.methodOn(UserController.class).getAllUsers())
.withSelfRel();
//For collections
userList.add(userLink);
Reference: https://spring.io/understanding/HATEOAS