Force GSON to use Constructor containing Setters or Setters in general, instead of Fields

Question

Let's say I have the following Model-class:

public class Product
{
    private int ProductId;
    private String Name;

    public Product(){
        setProductId(0);
        setName("");
    }

    // Getter and Setter for the Product-ID
    public void setProductId(int i){
        if(i >= 0) {
            ProductId = i;
        } else {
            ProductId = 0;
        }
    }
    public int getProductId(){
        return ProductId;
    }

    // Getter and Setter for the Name
    public void setName(String n){
        if(n != null && n.length() > 0) {
            name = n;
        } else {
            name = ""; 
        }
    }
    public String getName(){
        return name;
    }
}

The following Json-Strings:

"[{\"$id\":\"1\",\"ProductId\":1,\"Name\":\"A Product\"}," + 
"{\"$id\":\"2\",\"ProductId\":2,\"Name\":\"Another Product\"}]";

And

"[{\"$id\":\"1\",\"ProductId\":1,\"Name\":\"A Product\"}," + 
"{\"$id\":\"2\",\"ProductId\":-4,\"Name\":null}]";

And the following convertion method:

public void jsonToProducts(String json){
    ArrayList<Product> p = null;
    if(json != null && json.length() > 0){
        try{
            Type listType = new TypeToken<ArrayList<Product>>(){}.getType();
            p = new Gson().fromJson(json, listType);
        }
        catch(JsonParseException ex){
            ex.printStackTrace();
        }
    }
    setProducts(p);
}

By default Gson uses the fields. Because of that I get the following results of the two Json-Strings:

// Json-String 1:
Product 1: ProductId = 1; Name = "A Product";
Product 2: ProductId = 2; Name = "Another Product";

^ This is the result I want, so no problem here.

// Json-String 2:
Product 1: ProductId = 1; Name = "A Product";
Product 2: ProductId = -4; Name = null;

^ This is not the result I want, because for the second Product I want this instead:

Product 2: ProductId = 0; Name = "";

How can I force Gson to use the Setters instead?

I know how I can force Gson to use a Constructor that doesn't has any parameters, but can I also force Gson to use Setters? (Or perhaps a Constructor with parameters, then I'll just add another Constructor that got all Model's fields as parameters.)

Kevin Cruijssen · Accepted Answer · 2014-08-06T06:56:56.647

I've looked at Gson's User Guide and it looks like it isn't implemented yet.. Supporting Getters and Setters is placed on their TODO/issues-list (issue 232).

I've got a temporarily (inefficient and ugly solution):

public void jsonToProducts(String json){
    ArrayList<Product> products = null;
    if(json != null && json.length() > 0){
        try{
            Type listType = new TypeToken<ArrayList<Product>>(){}.getType();
            products = new Gson().fromJson(json, listType);
        }
        catch(JsonParseException ex){
            ex.printStackTrace();
        }
    }
    // TODO: Replace when Gson supports Setters or Parameterized Constructors
    if(products != null && products.size() > 0){
        for(Product p : products){
            p.setProductId(p.getProductId());
            p.setName(p.getName());
        }
    }

    setProducts(products);
}

I will accept this as answer for now. If anyone knows a better way of handling Gson's lack of Setter-support I would appreciate it. (Especially since my Product-List is around 1250 Products large, so looping through it resetting all fields isn't that good for performance in a mobile app. Luckily this only happens once at start-up..)

Force GSON to use Constructor containing Setters or Setters in general, instead of Fields

1 Answers1