jackson - 只有一个 Map 对象的数组字符串怎么转为 List<Map>
背景
有一个字符串长得像下面这个样子:
[{
"success": {
"description": "Welcome to JSON Viewer",
"code": 200
},
"message": "this is a message"
}]
想将其转化为 List<Map>对象,于是乎我这么写:
// json 为上面提到的字符串
List<Map<String, Object>> mapList = new ObjectMapper().convertValue(json, new TypeReference<List<Map<String, Object>>>() {});
执行报错:Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of ‘java.util.ArrayList<java.util.Map<java.lang.String,java.lang.Object>>’ out of VALUE_STRING token
查了一下原因是因为:转换的时候数组里面只有一个对象
,而这样是被默认禁止的。需要修改 jackson 的配置。
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);
List<Map<String, Object>> mapList = mapper.convertValue(json, new TypeReference<List<Map<String, Object>>>() {
});
执行依然报错:
Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `java.util.LinkedHashMap` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('[{
"success": {
"description": "Welcome to JSON Viewer",
"code": 200
},
"message": "this is a message"
}]')
简单翻译一下:无法构造LinkedHashMap的实例(尽管至少存在一个创建者)。
再改:不再使用convertValue方法,改用readValue
方法,直接搞定。
解决
// json 为上面提到的字符串
// 不过会有受检异常
List<Map<String, Object>> mapList = new ObjectMapper().readValue(json, new TypeReference<List<Map<String, Object>>>() {});
// 打印转换后的结果
System.out.println(mapList);
打印结果:
[{success={description=Welcome to JSON Viewer, code=200}, message=this is a message}]
posted on 2021-01-01 16:57 AmosChen 阅读(88) 评论(0) 编辑 收藏 举报 来源