Customizable Serialization for Activity Return Values in Durable Functions

What’s the problem?

Hey👋,

I'm working with Durable Functions in Java, and I’ve encountered an issue with how activity return values are serialized. Specifically:

• Activity functions return POJOs annotated with Jackson and Gson and having subTypes, which is deserialized using Gson when entering the activity but none is used for serializing return value.
• This creates inconsistencies.
• There's no way to customize the serialization mechanism for Durable Functions activities.
• Raises an Exception of InvalidTypeIdException because the type is missing at com.microsoft.durabletask.JacksonDataConverter#deserialize.

How to reproduce it?

Here’s a minimal Durable Function example where an Activity returns a POJO, but the Azure Functions Java Worker does not deserialize it properly:

1️⃣ POJO with Jackson & Gson annotations and Subtypes

import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.google.gson.annotations.JsonAdapter;
import com.google.gson.annotations.SerializedName;
import com.google.gson.*;
import java.io.IOException;

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
@JsonSubTypes({
    @JsonSubTypes.Type(value = AdminUser.class, name = "admin"),
    @JsonSubTypes.Type(value = RegularUser.class, name = "regular")
})
@JsonAdapter(UserTypeAdapter.class)
public abstract class User {
    private String id;

    private String name;

    public User() {}

    public User(String id, String name) {
        this.id = id;
        this.name = name;
    }

    public String getId() { return id; }
    public String getName() { return name; }
}

public class AdminUser extends User {
    private int adminLevel;

    public AdminUser() {}
    public AdminUser(String id, String name, int adminLevel) {
        super(id, name);
        this.adminLevel = adminLevel;
    }
}

public class RegularUser extends User {
    private String membershipStatus;

    public RegularUser() {}
    public RegularUser(String id, String name, String membershipStatus) {
        super(id, name);
        this.membershipStatus = membershipStatus;
    }
}

public class UserTypeAdapter extends TypeAdapter<User> {
    @Override
    public void write(JsonWriter out, User user) throws IOException {
        out.beginObject();
        out.name("type").value(user instanceof AdminUser ? "admin" : "regular");
        out.name("id").value(user.getId());
        out.name("name").value(user.getName());
        if (user instanceof AdminUser) {
            out.name("adminLevel").value(((AdminUser) user).adminLevel);
        } else if (user instanceof RegularUser) {
            out.name("membershipStatus").value(((RegularUser) user).membershipStatus);
        }
        out.endObject();
    }

    @Override
    public User read(JsonReader in) throws IOException {
        in.beginObject();
        String type = "";
        String id = "";
        String name = "";
        int adminLevel = 0;
        String membershipStatus = "";
        
        while (in.hasNext()) {
            String fieldName = in.nextName();
            switch (fieldName) {
                case "type":
                    type = in.nextString();
                    break;
                case "id":
                    id = in.nextString();
                    break;
                case "name":
                    name = in.nextString();
                    break;
                case "adminLevel":
                    adminLevel = in.nextInt();
                    break;
                case "membershipStatus":
                    membershipStatus = in.nextString();
                    break;
                default:
                    in.skipValue();
                    break;
            }
        }
        in.endObject();
        
        return "admin".equals(type) ? new AdminUser(id, name, adminLevel) : new RegularUser(id, name, membershipStatus);
    }
}

What do you want to happen?

✅ Supporting GSON for serialization.

Bắt đầu với com.microsoft.durabletask.JacksonDataConverter và theo dõi cách các giá trị trả về của activity được tuần tự hóa rồi giải tuần tự hóa. Sử dụng ví dụ User đa hình được cung cấp để hiểu lỗi, sau đó xác định cách tích hợp một Gson serializer có thể cấu hình. Được xem là hoàn tất khi các POJO của activity sử dụng chú thích Gson có thể round-trip mà không gặp InvalidTypeIdException do thiếu kiểu.