如何在gson序列化期间排除字段

Question

I have two entities: Order and Item in a OneToMany relationship. Item belongs an Order, and the Order has a set of Items.

class Order{
     @OneToMany(fetch = FetchType.EAGER, mappedBy = "id_order")
     Set<Item> items;
}

class Item{
     @ManyToOne(targetEntity = Order.class, fetch = FetchType.LAZY)
     @JoinColumn(name = "id_order")
     Order id_order;
}

I use gson to serialize Orders and send them to another machine, but a loop is being created during serialization, due to both orders and items having a reference to each other.

My goal is that when an Item is loaded, the field id_order should either be null or contain only the id, to avoid propagation. Does hibernate support this feature? Or can I exclude the field during serialization?

I already tried FetchType.LAZY on Item and catching Item inside an onLoad() Interceptor and setting its id_order to null . But it didn't work. I am trying to avoid writing a custom adapter or manually parsing all Items inside all Orders at every query.

Answer 1

I believe it has not much with Hibernate, but more with GSON. You should define serialization/deserialization rule.

Easiest way is to use @Expose annotation, to include/exclude given property from serialization/deserialization:

@Expose(serialize = false, deserialize = false)

Another way is to define custom adapters for givem class. WIth Adapter you can completely override the way GSON serialize or deserialize object.

For example:

public class YourAdapter implements JsonDeserializer<Order>, JsonSerializer<Order> {
    @Override
    public Orderde serialize(JsonElement jsonElement, Type type, JsonDeserializationContext jsonDeserializationContext) throws JsonParseException {
    // your logic
    }

    @Override
    public JsonElement serialize(Ordersrc, Type typeOfSrc, JsonSerializationContext context) {
        // your logic
    }
}

Finally initialize instance of your Gson parser:

Gson gson = new GsonBuilder()
        .registerTypeAdapter(Order.class, new YourAdapter())
        .build();

If you want to avoid writting whole serialization, you could exclude your field by using @Expose , and then write adapter with pure instance of GSON in it, serialize/deserialize using that pure one and manually add that one field.

Another way of dealing with serialization/deserialization problem is to use ExclusionStrategy described here: https://google-gson.googlecode.com/svn/trunk/gson/docs/javadocs/com/google/gson/ExclusionStrategy.html

Answer 2

I know this doesnt answer the question derectly but might help others, GSON has an option to exclude based on a vairiables modifier.

Gson gson = new GsonBuilder().excludeFieldsWithModifiers(Modifier.PRIVATE).create();