com.fasterxml.jackson.databind.exc.MismatchedInputException：无法从 START_OBJECT 令牌中反序列化 `java.util.Arra

Posted 2023-02-15

【中文标题】com.fasterxml.jackson.databind.exc.MismatchedInputException：无法从 START_OBJECT 令牌中反序列化 `java.util.ArrayList` 的实例

【英文标题】：com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of START_OBJECT token

【发布时间】：2020-02-20 16:37:39

【问题描述】：

如何使用JacksonObjectMapper阅读下面的JSON？我已经开发了代码，但遇到了错误。

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"
    ]
  

【问题讨论】：

请显示minimal reproducible example 与您的Java 实体和对ObjectMapper 的反序列化调用。

【参考方案1】：

您需要启用ACCEPT_SINGLE_VALUE_AS_ARRAY 功能。可能在POJO 中你有一个List，但是当List 中只有一个元素时，JSON 有效负载生成时没有数组括号。

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);