typeMismatch.java.util.List when trying to set a list

Question

I am trying to set a List<Long> to an Java object.

The set function is:

ResponseEntity<String> response = bcInsertService.addNewClip(new PrmBcClipInsert()
    .setTags(Arrays.asList(new Long[]{5L, 3L}))
);

And the object is

public class PrmBcClipInsert implements Serializable {

    @ApiModelProperty(required = true)
    private List<Long> tags;

    public List<Long> getTags() {
        return tags;
    }

    public PrmBcClipInsert setTags(List<Long> tags) {
        this.tags = tags;
        return this;
    }
}

This is BcInsertService:

public class BcInsertService extends RestTemplate {
    private static final Logger log = LoggerFactory.getLogger(BcInsertService.class);

    public ResponseEntity<String> addNewClip(PrmBcClipInsert prmBcClipInsert) {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.MULTIPART_FORM_DATA);
        MultiValueMap<String, Object> map= new LinkedMultiValueMap<String, Object>();
        HttpEntity<MultiValueMap<String, Object>> request = new HttpEntity<MultiValueMap<String, Object>>(prmBcClipInsert.getParameters(), headers);

        ParameterizedTypeReference<StandardResponse> typeRef = new ParameterizedTypeReference<StandardResponse>() {};
        ResponseEntity<String> response = this.postForEntity( "http://localhost:8080/bc/add-clip", request , String.class );
        log.info(response.toString());
        return response;
    }

}

And it returns an error:

Field error in object 'prmBcClipInsert' on field 'tags': rejected value [[5,3]]; codes [typeMismatch.prmBcClipInsert.tags,typeMismatch.tags,typeMismatch.java.util.List,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [prmBcClipInsert.tags,tags]; arguments []; default message [tags]]; default message [Failed to convert property value of type 'java.lang.String' to required type 'java.util.List' for property 'tags'; nested exception is java.lang.NumberFormatException: For input string: "[5,3]"]

Why the method doesn't accept a list even though it says that it accepts a list?

Answer 1

I was able to recreate your error case using a form validation. You are probably trying to pass a form data that is [5, 3] for the tags variable with type List<Long>, but passing with brackets break that structure, the value ought to be 5, 3...

So what I've done is;

1. Create a dummy controller using your input;

   @Controller
   public class TestController {
   
       @PostMapping
       public ModelAndView test(@Validated @ModelAttribute final PrmBcClipInsert prmBcClipInsert, final BindingResult bindingResult) {
           final ModelAndView modelAndView = new ModelAndView();
           System.out.println(prmBcClipInsert.getTags());
           modelAndView.setViewName("test");
           return modelAndView;
       }
   }
   

2. Pass the form with tags=[5,3], and get the following error in BindingResult;

   org.springframework.validation.BeanPropertyBindingResult: 1 errors Field error in object 'prmBcClipInsert' on field 'tags': rejected value [[5, 3]]; codes [typeMismatch.prmBcClipInsert.tags,typeMismatch.tags,typeMismatch.java.util.List,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [prmBcClipInsert.tags,tags]; arguments []; default message [tags]]; default message [Failed to convert property value of type 'java.lang.String' to required type 'java.util.List' for property 'tags'; nested exception is java.lang.NumberFormatException: For input string: "[5,3]"]

   Which is the identical error that you were getting... So I presume either you get this PrmBcClipInsert as a form input like in my example, or you are trying to do a similar binding in some other part of your code...

3. Pass the form with tags=5,3, no error...

---

There can be a custom converter to support for passing said array input with brackets in binding logic with something like;

@Component
public class LongListConverter implements Converter<String, List<Long>> {

    @Override
    public List<Long> convert(String source) {
        return Arrays.stream(StringUtils.strip(source, "[]").split(","))
                .map(StringUtils::strip)
                .map(Long::new)
                .collect(Collectors.toList());
    }
}

With this, both 5, 3 & [5, 3] can be supplied as value of tags variable.

Answer 2

All you need is a converter here. Create a List<>String converter like below (refactor the below example in your code):

@Converter
public class StringListConverter implements AttributeConverter<List<String>, String> {
    private static final String SPLIT_CHAR = ";";

    // Go nuts on List to string here...

    @Override
    public String convertToDatabaseColumn(List<String> stringList) {
        return String.join(SPLIT_CHAR, stringList.toString());
    }

    @Override
    public List<String> convertToEntityAttribute(String string) {
        return Arrays.asList(string.split(SPLIT_CHAR));
    }
}

Try it and share the outcome.