CustomDeserializer has no default constructor (no argument)

Question

I consume REST Api with RestTemplate. The response I get from the API has many nested objects. Here is a small snippet as an example:

"formularios": [
  {
    "form_data_id": "123006",
    "form_data": {
      "form_data_id": "123006",
      "form_id": "111",
      "efs": {
        "1": {},
        "2": "{\"t\":\"c\",\"st\":\"m\",\"v\":[{\"id\":\"3675\",\"l\":\"a) Just an example\",\"v\":\"1\"},{\"id\":\"3676\",\"l\":\"b) Another example.\",\"v\":\"2\"}]}"
      }
    }

The problem I am facing is that in most cases, “1” does have content, like “2”, and Jackson just parses it as a String on the “efs” object. But sometimes, as in the code snippet, the API sends it empty, and the jackson accepts it as an object, which gives me an error that says something about START_OBJECT (I don’t remember the exact error, but this is not important for this question).

So I decided to create my own deserializer, so when Jackson reads "1", he ignores the empty object and simply parses it as an empty string.

:

public class CustomDeserializer extends StdDeserializer<Efs> {

 public CustomDeserializer(Class<Efs> t) {
     super(t);
 }

 @Override
 public Efs deserialize(JsonParser jp, DeserializationContext dc)
         throws IOException, JsonProcessingException {

     String string1 = null;
     String string2 = null;
     JsonToken currentToken = null;

     while ((currentToken = jp.nextValue()) != null) {
         if (currentToken.equals(JsonToken.VALUE_STRING)) {
             if (jp.getCurrentName().equals("1")) {
                 string1 = jp.getValueAsString();
             } else {
                 string2 = jp.getValueAsString();
             }

         } else {
             if (jp.getCurrentName().equals("2")) {
                 string2 = jp.getValueAsString();
             }

         }
     }
     return new Efs(string1, string2);

  }
 }

API:

    ObjectMapper mapper = new ObjectMapper();  
    SimpleModule mod = new SimpleModule("EfsModule");
    mod.addDeserializer(Efs.class, new CustomDeserializer(Efs.class));
    mapper.registerModule(mod);


    List<HttpMessageConverter<?>> messageConverters = new ArrayList<>();
    MappingJackson2HttpMessageConverter jsonMessageConverter = new MappingJackson2HttpMessageConverter();
    jsonMessageConverter.setObjectMapper(mapper);
    messageConverters.add(jsonMessageConverter);


    RestTemplate restTemplate = new RestTemplate();
    restTemplate.setMessageConverters(messageConverters);

:

 CustomDeserializer has no default (no arg) constructor

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Answer 1

, . , ( , ):

public class CustomDeserializer extends StdDeserializer<Efs> {

   public CustomDeserializer() {
       super(Efs.class);
   }
   ...
}

Answer 2

, ( ). ( ), :

@JsonDeserialize(using = DomainObjectDeserializer.class)
public class DomainObject {
    private String key;

    public class DomainObjectDeserializer extends StdDeserializer<DomainObject> {
        public DomainObjectDeserializer() {
            super(DomainObject.class);
        }

        @Override
        public DomainObject deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
            // code
        }
    }
}

Class # getDeclaredConstructor() ( vararg), : ( ). DomainObjectDeserializer , DomainObjectDeserializer javac , . , DomainObjectDeserializer .

DomainObjectDeserializer.class.getDeclaredConstructors() , , .

DomainObjectDeserializer static .

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Answer 3

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