Can not deserialize instance of java.lang.String out of START_OBJECT token String.class

Question

I come across using ObjectMapper with String.class for first time.I tried giving json as string for which got JsonMappingException. Could you please help understand why?

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);
   }

Response:

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)

On just a trial when i pass response as "success", i get:

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

rkosegi · Accepted Answer · 2018-09-03 10:47:03Z

1

Correct way is to read it as tree:

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

outputs: success

answered Sep 3, 2018 at 10:47

rkosegi

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Comments

Alexander Petrov · Accepted Answer · 2018-09-03 10:39:24Z

0

Because you passed json pair where response is a field name and success is a value for this field so you need to create class ResponseDTO

public class ResponseDto { private String response; //getter/setter here

and

 Object object = objectMapper.readValue(response, ResponseDTO.class);

Hope it helps.

answered Sep 3, 2018 at 10:39

Alexander Petrov

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5 Comments

Gayathri Over a year ago

My need is on response which is applicable for String.class

Alexander Petrov Over a year ago

Well just a simple text in response without Json structure will be ok.

Gayathri Over a year ago

I tried with just "success" but i got jsonparseException. i have added that too in question

Alexander Petrov Over a year ago

I meant that you don't need to use ObjectMapper in this case. If your response is just a String you could use it as is.

Gayathri Over a year ago

You're actually right. I ain't sure. This is existing code. was writing junit for a method which implements this

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