Spring Rest - bind nested DTO object to @RequestParams

Question

I want to bind get params to my DTO. My problem is mapping the nested list my DTO has.

controller class:

@PostMapping(value = "test-endpoint")
public ResponseEntity<String> doStuff(@Valid @RequestParams MyDto myDto) {
    // do stuff
}

parent DTO:

public class MyDto {
    @NotNull
    private String fieldA;

    @Valid
    @NotNull
    private List<MyNestedDto> nestedDto;
}

Nested DTO:

public class MyNestedDto {
    @NotNull
    private String nestedFieldA;

    @NotNull
    private String nestedFieldB;

    // more fields
}

I have a service that sends a POST request to my controller. The request cannot be changed hence why I can't use @RequestBody annotation.

The request looks like that:

http://localhost:8080/api/test-endpoint?nestedDto={"more":[{"nestedFieldA":"example","nestedFieldB":"example"}]}&fieldA=123

Is there a way to bind the nested list to get params?

Edit*

Registering a converter doesn't seem to work, my converter convert method is not even called.

@Configuration
public class WebConfiguration implements WebMvcConfigurer {
    @Override
    public void addFormatters(FormatterRegistry registry) {
        registry.addConverter(new MyConverter());
    }
}

public class MyConverter implements Converter<String, MyDto> {

    @Override
    public MyDto convert(String source) {
        // it never reaches there
        ObjectMapper objectMapper = new ObjectMapper();
        
        return null; // return null for testing purposes
    }
}

sorry what is problem ? do you want to map that JSON to `@RequestParam` — Ryuzaki L, Dec 14 '20 at 16:15
yes is there a way to map that JSON to @RequestParam without changing the request? — Thanos M, Dec 14 '20 at 16:19
Why you use `POST` method and the do everything on semantics of `GET`? Either `POST` your object and get it from `@RequestBody` or use `GET` and receive each params independently or use Map. Recommendation: Use `POST/@RequestBody`. — Rana_S, Dec 14 '20 at 18:49
I cannot use @RequestBody because as I said I cannot modify the incoming request that is being made to my controller. — Thanos M, Dec 14 '20 at 19:11
The main problem is not the request method but how to bind my nested dto to get params as described — Thanos M, Dec 14 '20 at 19:15
Bind HttpServletRequest to controller method then get parameters and use objectMapper to convert it to object — Gurkan İlleez, Dec 14 '20 at 19:22
I would prefer a more elegant way, I want to avoid deserializing those params inside my controller manually. Doing that in most of my controllers is not the way to go in my opinion. — Thanos M, Dec 14 '20 at 19:24

score 1 · Answer 1 · answered Dec 14 '20 at 19:31

1

public class AController {
     private final ObjectMapper objectMapper;
     private final Validator validator;

     public AController(ObjectMapper objectMapper,Validator validator){
          this.objectMapper = objectMapper;
          this.validator = validator;
     }

     @PostMapping(value = "test-endpoint")
     public ResponseEntity<String> doStuff(@RequestParam("nestedDto") String nestedDto) {
           MyDto myDto = objectMapper.readValue(nestedDto);
           Set<ConstraintViolation<MyDto>> constraintViolation = 
           validator.validate(myDto);
           if (!constraintViolation.isEmpty()) {
                throw new ConstraintViolationException(constraintViolation);
           }
     }

}

This is pseudo code so i just write it to demonstrate how to solve the problem. If you want more elegant way, you have to change request because request is wrong here.

answered Dec 14 '20 at 19:31

Gurkan İlleez

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Thank you for your answer, I was aware of this solution before posting this question. As I said I would like to know if there is a more elegant way of doing this deserialization since it's not convenient doing that in most of my controllers. – Thanos M Dec 14 '20 at 19:35
https://stackoverflow.com/questions/38360215/how-to-create-a-spring-interceptor-for-spring-restful-web-services – Gurkan İlleez Dec 14 '20 at 19:42
I ll check it out thanks, I was thinking of using a custom converter but I don't seem to be able to make it work. – Thanos M Dec 14 '20 at 19:44

Spring Rest - bind nested DTO object to @RequestParams

1 Answers1