javademos/sealed/jackson/JsonPayment.java

import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import tools.jackson.databind.json.JsonMapper;

public class JsonPayment {
    // Two annotations tell Jackson which JSON field names the type, and which class each name means.
    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
    @JsonSubTypes({
        @JsonSubTypes.Type(value = Card.class, name = "card"),
        @JsonSubTypes.Type(value = Upi.class, name = "upi"),
        @JsonSubTypes.Type(value = NetBanking.class, name = "netbanking")})
    sealed interface Payment permits Card, Upi, NetBanking {}
    record Card(String last4, long amount) implements Payment {}
    record Upi(String vpa, long amount) implements Payment {}
    record NetBanking(String bank, long amount) implements Payment {}

    static long fee(Payment p) {
        return switch (p) {
            case Card(String last4, long amount) -> amount * 2 / 100;
            case Upi(String vpa, long amount) -> 0;
            case NetBanking(String bank, long amount) -> 15;
        };
    }

    public static void main(String[] args) {
        JsonMapper mapper = JsonMapper.builder().build();
        Payment[] all = { new Card("4242", 500), new Upi("ankur@bank", 500), new NetBanking("HDFC", 500) };
        for (Payment p : all) {
            String json = mapper.writeValueAsString(p);
            Payment back = mapper.readValue(json, Payment.class);
            System.out.println(json + "  ->  " + back + "  equal=" + back.equals(p) + "  fee=" + fee(back));
        }
        try {
            mapper.readValue("{\"type\":\"cheque\",\"amount\":500}", Payment.class);
        } catch (Exception e) {
            System.out.println("unknown type: " + e.getClass().getSimpleName() + ": " + e.getMessage().lines().findFirst().orElse(""));
        }
    }
}