JsonMappingException没有单一的String构造函数/工厂方法Jackson [英] JsonMappingException no single-String constructor/factory method Jackson

问题描述

我正在尝试解析使用Spring build Jackson支持从我的Controller中的UI发送的JSON数据，这是我的代码

I am trying to parse JSON data being sent from UI in my Controller using Spring build Jackson support and this is my code

final Map<String, CartDataHelper> entriesToUpdateMap = new ObjectMapper().readValue(entriesToUpdate, new TypeReference<Map<String, CartDataHelper>>()

我的JSON字符串是

{"0":"{\"categoryCode\":\"shoes\",\"productCode\":\"300050253\",\"initialQty\":\"3\",\"leftoverQty\":\"0\",\"newQty\":\"3\"}",
"1":"{\"categoryCode\":\"shoes\",\"productCode\":\"300050254\",\"initialQty\":\"3\",\"leftoverQty\":\"0\",\"newQty\":\"3\"}"}

我使用一些在线服务检查了JSON格式并且它似乎有效，而tryin gto解析JSON数据我得到以下异常

i checked the JSON format using some online services and it seems valid, while tryin gto parse JSON data i am getting following exception

org.codehaus.jackson.map.JsonMappingException: Can not instantiate value of type [simple type, class controllers.util.CartDataHelper] from JSON String; no single-String constructor/factory method

my CartDataHelper class包含 productCode ， categoryCode 等的简单属性，带有无参数构造函数

my CartDataHelper class contains simple properties for for productCode, categoryCode etc with a no argument constructor

推荐答案

正如评论所述，您的JSON包含 Map< String，String> 而不是 Map< String，CartDataHelper> ：值是JSON字符串，而不是JSON对象。

As comments mentioned, your JSON contains Map<String,String> and NOT Map<String,CartDataHelper>: values are JSON Strings, not JSON Objects.

理想情况下你不会尝试写作将对象作为JSON字符串;如果是这样，事情会奏效。

Ideally you would not try writing out objects as JSON Strings; and if so, things would work.

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