com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of START_OBJECT token

Question

How to read below JSON using Jackson ObjectMapper? I have developed code but getting below error.

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of START_OBJECT token
 at [Source: (File); line: 7, column: 19] (through reference chain: com.example.demo.resources.Orgnization["secondaryIds"])

JSON

{
  "id": "100000",
  "name": "ABC",
  "keyAccount": false,
  "phone": "1111111",
  "phoneExtn": "11",
  "secondaryIds": {
    "ROP": [
      "700010015",
      "454546767",
      "747485968",
      "343434343"
    ],
    "AHID": [
      "01122006",
      "03112001"
    ]
  }
}

Please show a minimal reproducible example with your Java entity and deserialization call to ObjectMapper. — Mark Rotteveel
– Mark Rotteveel, Commented Oct 24, 2019 at 15:26
May be you use: mapper.readValue(is, List.class) instead of mapper.readValue(is, Map.class) — nik0x1
– nik0x1, Commented Feb 26, 2023 at 18:11

Michał Ziober · Accepted Answer · 2019-10-24 15:27:30Z

27

You need to enable ACCEPT_SINGLE_VALUE_AS_ARRAY feature. Probably in POJO you have a List but when there is only one element in a List JSON payload is generated without array brackets.

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;
import java.util.List;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./src/main/resources/test.json");

        ObjectMapper mapper = new ObjectMapper();
        mapper.enable(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY);

        Orgnization root = mapper.readValue(jsonFile, Orgnization.class);
        System.out.println(root);
    }
}

edited Oct 24, 2019 at 15:27

answered Oct 24, 2019 at 15:16

Michał Ziober

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