java - 无法从 START_OBJECT 标记 String.class 反序列化 java.lang.String 的实例

Question

我第一次遇到将 ObjectMapper 与 String.class 一起使用。我尝试将 json 作为字符串给出，但得到了 JsonMappingException。您能帮忙解释一下原因吗？

public static void main(String args[]) throws JsonParseException, JsonMappingException, IOException{
       String response="{\"response\":\"success\"}";
       ObjectMapper objectMapper = new ObjectMapper();
        Object object = objectMapper.readValue(response, String.class);
        System.out.println(object);
   }

回应:

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.lang.String out of START_OBJECT token at [Source: {"response":"success"}; line: 1, column: 1] at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:270) at com.fasterxml.jackson.databind.DeserializationContext.reportMappingException(DeserializationContext.java:1234) at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1122) at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1075) at com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:60) at com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:11) at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3814) at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2858)

在一次试验中，当我将响应传递为“成功”时，我得到:

Exception in thread "main" com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'success': was expecting ('true', 'false' or 'null')

Answer 1

正确的方法是read it as tree :

ObjectMapper om = new ObjectMapper();
JsonNode tree = om.readTree("{\"response\":\"success\"}");
String response = tree.get("response").asText();
System.out.println(response);

输出:成功