SpringBoot JSON not deserializing into my request model - json

Question

I am using SpringBoot and trying to deserialize JSON like:
{
"userId": "Dave",
"queryResults": {
"id": "ABC",
"carData": {.....},
"carId": "Honda",
"status": 0,
"model": "X"
}
}
, into MyRequestModel clas:
public class MyRequestModel {
private String userId;
private String: queryResults;
}
, that is received as #RequestBody parameter in my #PostMapping method that looks like:
#PostMapping
public String postDate(#RequestBody MyRequestModel data) {
...
return "posted";
}
The above queryResults field is supposed to be stored as a CLOB in a database.
Problem I am having is that if I send this JSON to hit my endpoint (PostMapping) method, it cannot deserialize it into MyRequestModel and I get this error:
Cannot deserialize instance of java.lang.String out of START_OBJECT token
at [Source: (PushbackInputStream); line: 3, column: 18] (through reference chain: MyRequestModel["queryResults"])]

Answer 1

I guess the real answer to your question is: if you NEED the queryResults property to be a String, then implement a custom deserializer.
If not, then, use one of the alternatives that Jonatan and Montaser proposed in the other answers.
Implementing a custom deserializer within Spring Boot is fairly straightforward, since Jackson is its default serializer / deserializer and it provides a easy way to write our own deserializer.
First, create a class that implements the StdDeserializer<T>:
MyRequestModelDeserializer.java
public class MyRequestModelDeserializer extends StdDeserializer<MyRequestModel> {
public MyRequestModelDeserializer() {
this(null);
}
public MyRequestModelDeserializer(Class<?> vc) {
super(vc);
}
#Override
public MyRequestModel deserialize(JsonParser p, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
JsonNode node = p.getCodec().readTree(p);
String userId = node.get("userId").asText();
String queryResults = node.get("queryResults").toString();
MyRequestModel model = new MyRequestModel();
model.setQueryResults(queryResults);
model.setUserId(userId);
return model;
}
}
Second, mark your class to be deserialized using your custom deserializer by using the #JsonDeserialize annotation:
MyRequestModel.java
#JsonDeserialize(using = MyRequestModelDeserializer.class)
public class MyRequestModel {
private String userId;
private String queryResults;
}
It's done.

Answer 2

queryResults is a String on Java side but it is an Object on JSON side.
You will be able to deserialize it if you send it in as a String:
{
"userId": "Dave",
"queryResults": "foo"
}
or if you create classes that maps to the fields:
public class MyRequestModel {
private String userId;
private QueryResults queryResults;
}
public class QueryResults {
private String id;
private CarData carData;
private String carId;
private Integer status;
private String model;
}
or if you serialize it into something generic (not recommended):
public class MyRequestModel {
private String userId;
private Object queryResults;
}
public class MyRequestModel {
private String userId;
private Map<String, Object> queryResults;
}
public class MyRequestModel {
private String userId;
private JsonNode queryResults;
}

Answer 3

You have two options to deserialize this request:-
change the type of queryResults to Map<String, Object>, it will accepts everything as an object of key and value. (Not recommended)
public class MyRequestModel {
private String userId;
private Map<String, Object> queryResults;
}
You have to create a class that wraps the results of queryResults as an object.
class QueryResult {
private String id;
private Map<String, Object> carData;
private String carId;
private Integer status;
private String model;
public QueryResult() {}
public QueryResult(String id, Map<String, Object> carData, String carId, Integer status, String model) {
this.id = id;
this.carData = carData;
this.carId = carId;
this.status = status;
this.model = model;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public Map<String, Object> getCarData() {
return carData;
}
public void setCarData(Map<String, Object> carData) {
this.carData = carData;
}
public String getCarId() {
return carId;
}
public void setCarId(String carId) {
this.carId = carId;
}
public Integer getStatus() {
return status;
}
public void setStatus(Integer status) {
this.status = status;
}
public String getModel() {
return model;
}
public void setModel(String model) {
this.model = model;
}
}
and make the type of queryResult as shown:-
public class MyRequestModel {
private String userId;
private QueryResult queryResults;
}