How to change Hateoas output format in spring application? - spring

Question

I am currently working on a spring application that offers a REST interface with which CRUD operations on entities of various kinds can be performed. These entities are stored in repositories and thus a major part of the REST interface is automatically generated by spring. When I execute a GET request on such an entity type (e.g. /devices), the result looks as following:
{
"_embedded":{
"devices":[
{
"macAddress": "...",
"ipAddress": "...",
"name": "Device_1",
"id":"5c866db2f8ea1203bc3518e8",
"_links":{
"self":{
...
},
"device":{
...
}
}, ...
]
},
"_links":{
...
},
"page":{
"size":20,
"totalElements":11,
"totalPages":1,
"number":0
}
}
Now I need to implement a similar interface manually, because additional checks are required. I have made use of the spring-hateoas features for this purpose. However, I am unable to achieve the same output structure like the one automatically generated by spring. The corresponding code in my controller class (annotated with RestController) looks as follows:
#GetMapping("/devices")
public Resources<Device> getDevices() {
List<Device> deviceList = getDeviceListFromRepository();
Link selfRelLink = ControllerLinkBuilder.linkTo(
ControllerLinkBuilder.methodOn(RestDeviceController.class)
.getDevices())
.withSelfRel();
Resources<Device> resources = new Resources<>(deviceList);
resources.add(selfRelLink);
return resources;
}
The configuration (excerpt) looks as follows:
#Configuration
#EnableWebMvc
#EnableSpringDataWebSupport
#EnableHypermediaSupport(type = EnableHypermediaSupport.HypermediaType.HAL)
public class WebServletConfiguration extends WebMvcConfigurerAdapter implements ApplicationContextAware {
...
#Override
public void configureContentNegotiation(ContentNegotiationConfigurer c) {
c.defaultContentType(MediaTypes.HAL_JSON);
}
...
}
However, this is the output of a request:
{
"links":[
{
"rel":"self",
"href":"..."
}
],
"content":[
{
"id":"5c866db2f8ea1203bc3518e8",
"name":"Device_1",
"macAddress": "...",
"ipAddress":"...",
}
]
}
As you can see, instead of an _embedded key there is a content key and the links key misses the leading underscore. These are the main issues I have with this output, more detailed differences compared to the output above are not that important to me. I would like to unify the ouput generated by my application, but I am unable to achieve the output format of the mappings that are automatically generated by spring. I also tried to wrap the resources object into another resource object (like return new Resource<...>(resources)), this did not work as well though.
Do you have any hints for me about what I am doing wrong here? I am quite new to Spring & Co, so please tell me if you need more information about a certain thing. Any help is highly appreciated. Thanks in advance!

Answer 1

Finally I was able to find a solution: The strange output format as showed in the question was generated due to the accept header application/json that was sent by the client. After adding
#Override
public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
configurer.ignoreAcceptHeader(true);
configurer.defaultContentType(MediaTypes.HAL_JSON);
}
to class WebServletConfiguration which extends WebMvcConfigurerAdapter everything works as exptected and the output format is now HAL-like. A quite easy fix, but it took me weeks to figure this out. Maybe this answer will help somebody else in the future.