CODEWITHSUNDEEP
javadeserializationgson
t3rse
t3rse

Reputation: 10124

Gson Deserialization - Nested Classes Mapping Lowercase Fields

I am currently using Gson libraries to deserialize a json file into some java class instances. Everything seems to work fine but I encounter issues with nested classes with lowercase field definitions. My FieldNamingPolicy is set to FieldNamingPolicy.UPPER_CAMEL_CASE which works for everything in the hierarchy except the items in my nested class that have lowercase (as opposed to PascalCase) field names.

Is there something special involved in having mixed cases used in the JSON being parsed?

I'm not sure my explanation makes sense so here is a contrived example of what my json looks like and the problem I'm running into: 

{
    "Name": "David",
    "City": "Los Angeles",
    "Website": "http://www.example.org/1",
    "Contact": {
      "AllowPhone": "true",
      "Priority": "10",
      "Address": {
        "street": "1234 Example St",
        "city": "Los Angeles",
        "state": "CA",
        "phone": "(777)777-7777"
      }
    }
}

I have classes based on this hierarchy:

  1. PersonModel (with fields for Name, City, State, Website, and Contact)
  2. ContactModel (with fields for AllowPhone, Priority, Address)
  3. AddressModel (with fields for street, city, state, phone)

Examples of the classes: 

public class PersonModel{

  @Expose
  String name;

  @Expose
  String city;

  @Expose
  String website;

  @Expose
  ContactModel contact;

  /* getters for all the above defined */
}

public class ContactModel{

  @Expose
  String allowPhone;

  @Expose
  int priority;

  @Expose
  AddressModel address;

  /* getters for all the above defined */

}

public class AddressModel{ /* fields are lower case! */

  @Expose
  String street;

  @Expose
  String city;

  @Expose
  String state;

  @Expose
  String phone; 

  /* getters for all the above defined */

}

When I attempt to deserialize json into my class structure Person and Contact work as expected. I even get an instance of AddressModel. However the fields on the instance of AddressModel are all null.

Can anyone point me to either a fix for the case issue or, if there is something else wrong, an adjusted approach?

Upvotes: 1

Views: 675

Answers (1)

Sotirios Delimanolis
Sotirios Delimanolis

Reputation: 279890

As the javadoc states, GsonBuilder#setFieldNamingPolicy(FieldNamingPolicy)

Configures Gson to apply a specific naming policy to an object's field during serialization and deserialization.

So fields mapped like

Java name | Json name
   name   |  Name

have to also work for deserialization. They work for your PersonModel and ContactModel because the policy holds true.

However, for your AddressModel class, it looks like

Java name | Json name
  street  |  street

So the policy is not upheld and Gson doesn't find those fields to deserialize them.

I suggest using @SerializedName to specify exactly what the name in the JSON will be.

Upvotes: 1

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