Main

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonValue;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.module.SimpleModule;

import java.io.IOException;
import java.util.List;


public class Main {
    private static final String json ="{\"result\": \"some result\"}";
    private static final String json2 ="\"ERROR\"";
    public static void main(String[] args) throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        SimpleModule module = new SimpleModule();
        module.addDeserializer(SearchResultDTO.class, new SearchResultsDeserializer());
        mapper.registerModule(module);
        SearchResultDTO obj1 = mapper.readValue(json,SearchResultDTO.class);
        SearchResultDTO obj2 = mapper.readValue(json2,SearchResultDTO.class);
        System.out.println(obj1);
        System.out.println(obj2);
    }


    private static class SearchResultDTO {
        private String result;

        public SearchResultDTO() {
        }

        public SearchResultDTO(String result) {
            this.result = result;
        }

        public String getResult() {
            return result;
        }

        public void setResult(String result) {
            this.result = result;
        }

        @Override
        public String toString() {
            return "SearchResultDTO{" +
                    "result='" + result + '\'' +
                    '}';
        }
    }

    public static class SearchResultsDeserializer extends JsonDeserializer<SearchResultDTO> {
        private static ObjectMapper mapper = new ObjectMapper();
        @Override
        public SearchResultDTO deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException {
            JsonToken t = jp.getCurrentToken();
            if (t == JsonToken.VALUE_STRING){
                return new SearchResultDTO(jp.getText());
            } else {
                return mapper.readValue(jp, SearchResultDTO.class);
            }
        }
    }
}

Output:
SearchResultDTO{result='some result'}
SearchResultDTO{result='ERROR'}