How to handle a NumberFormatException with Gson in deserialization a JSON response

Question

I\'m reading a JSON response with Gson, which returns somtimes a NumberFormatException because an expected int value is set to an empty string. Now

Answer 1

At first, I tried to write a general custom type adaptor for Integer values, to catch the NumberFormatException and return 0, but Gson doesn't allow TypeAdaptors for primitive Types:

java.lang.IllegalArgumentException: Cannot register type adapters for class java.lang.Integer

After that I introduced a new Type FooRuntime for the runtime field, so the Foo class now looks like this:

public class Foo
{
    private String name;
    private FooRuntime runtime;

    public int getRuntime()
    {
        return runtime.getValue();
    }
}

public class FooRuntime
{
    private int value;

    public FooRuntime(int runtime)
    {
        this.value = runtime;
    }

    public int getValue()
    {
        return value;
    }
}

A type adaptor handles the custom deserialization process:

public class FooRuntimeTypeAdapter implements JsonDeserializer, JsonSerializer
{
    public FooRuntime deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException
    {
        int runtime;
        try
        {
            runtime = json.getAsInt();
        }
        catch (NumberFormatException e)
        {
            runtime = 0;
        }
        return new FooRuntime(runtime);
    }

    public JsonElement serialize(FooRuntime src, Type typeOfSrc, JsonSerializationContext context)
    {
        return new JsonPrimitive(src.getValue());
    }
}

Now it's necessary to use GsonBuilder to register the type adapter, so an empty string is interpreted as 0 instead of throwing a NumberFormatException.

String input = "{\n" +
               "   \"name\" : \"Test\",\n" +
               "   \"runtime\" : \"\"\n" +
               "}";

GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(FooRuntime.class, new FooRuntimeTypeAdapter());
Gson gson = builder.create();
Foo foo = gson.fromJson(input, Foo.class);