Using Custom JSON Deserialization in Jackson - json

Question

I am trying to create objects of a complex class with the Jackson library. Each object has a schema that the deserializer needs to use to interpret the JSON. My question is how to supply the schema to the deserializer?
The deserializer extends the class JSONDeserializer, which has a no-argument constructor and an abstract method deserialize(parser,context) that must be overridden. I would like to use instead the alternate method deserialize(parser,context, value) where value is the partially constructed object, which includes the schema. That is, the deserialize method could call value.schema() to access the schema. The object itself is constructed piecewise with a builder, which the alternate method uses.
I have found no documentation on how to register the alternate deserialize method with the object mapper to insure that it, rather than the overridden abstract method, is called.
Any advice would be appreciated.

Answer 1

So Lets say you have a class called User which has a which has a property called Data which has date field birthdate, and you don't want to use the standard Date deserializer and wants to use your custom one. below is how it can be achieved.
User.java
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
#JsonIgnoreProperties(ignoreUnknown = true)
public class User {
#JsonProperty("code")
public Integer code;
#JsonProperty("status")
public String status;
#JsonProperty("message")
public String message;
#JsonProperty("time")
public String time;
#JsonProperty("data")
public Data data;
}
Data.java
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
#JsonIgnoreProperties(ignoreUnknown = true)
public class Data {
#JsonProperty("id_hash")
public Integer idHash;
#JsonProperty("user_name")
public String userName;
#JsonProperty("user_surname")
public String userSurname;
#JsonProperty("birthdate")
#JsonDeserialize(using = BirthdayDeserializer.class)
public Date birthdate;
#JsonProperty("height")
public Integer height;
#JsonProperty("weight")
public Integer weight;
#JsonProperty("sex")
public Integer sex;
#JsonProperty("photo_path")
public String photoPath;
}
BirthdayDeserializer.java
public class BirthdayDeserializer extends JsonDeserializer<Date> {
#Override
public Date deserialize(JsonParser jsonparser, DeserializationContext deserializationcontext) throws IOException {
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String date = jsonparser.getText();
try {
return format.parse(date);
} catch (ParseException e) {
throw new RuntimeException(e);
}
}
}
Main.java to test it.
public class Main {
public static void main(String[] args) throws IOException {
String json = "{\n" +
" \"code\": 1012,\n" +
" \"status\": \"sucess\",\n" +
" \"message\": \"Datos Del Usuario\",\n" +
" \"time\": \"28-10-2015 10:42:04\",\n" +
" \"data\": {\n" +
" \"id_hash\": 977417640,\n" +
" \"user_name\": \"Daniel\",\n" +
" \"user_surname\": \"Hdz Iglesias\",\n" +
" \"birthdate\": \"1990-02-07\",\n" +
" \"height\": 190,\n" +
" \"weight\": 80,\n" +
" \"sex\": 2\n" +
" }\n" +
"}";
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(Date.class, new BirthdayDeserializer());
mapper.registerModule(module);
User readValue = mapper.readValue(json, User.class);
System.out.println(readValue);
}
}
Check the main method as how I have registered the custom Deserializer.