sealed: add release-level and Jackson 3.2.3 transcripts

09 shows which language level each sealed feature needs; 10 runs the Payment model through Jackson 3 (jars fetched and sha1-checked, not committed).

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01TF9JWFvJSNm6HVzswzZU5a

sealed/jackson/.gitignore

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+lib/

sealed/jackson/JsonForgotten.java

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+import com.fasterxml.jackson.annotation.JsonSubTypes;
+import com.fasterxml.jackson.annotation.JsonTypeInfo;
+import tools.jackson.databind.json.JsonMapper;
+
+public class JsonForgotten {
+    // Wallet is a permitted subtype, and the compiler is happy, but nobody told Jackson about it.
+    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
+    @JsonSubTypes({
+        @JsonSubTypes.Type(value = Card.class, name = "card"),
+        @JsonSubTypes.Type(value = Upi.class, name = "upi")})
+    sealed interface Payment permits Card, Upi, Wallet {}
+    record Card(long amount) implements Payment {}
+    record Upi(long amount) implements Payment {}
+    record Wallet(long amount) implements Payment {}
+
+    public static void main(String[] args) {
+        JsonMapper mapper = JsonMapper.builder().build();
+        System.out.println("write : " + mapper.writeValueAsString(new Wallet(500)));
+        try {
+            mapper.readValue("{\"type\":\"wallet\",\"amount\":500}", Payment.class);
+        } catch (Exception e) {
+            System.out.println("read  : " + e.getClass().getSimpleName() + ": " + e.getMessage().lines().findFirst().orElse(""));
+        }
+    }
+}

sealed/jackson/JsonNoSubTypes.java

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+import com.fasterxml.jackson.annotation.JsonTypeInfo;
+import tools.jackson.databind.json.JsonMapper;
+
+public class JsonNoSubTypes {
+    // Only @JsonTypeInfo, no @JsonSubTypes. Does Jackson find the permitted subclasses by itself?
+    @JsonTypeInfo(use = JsonTypeInfo.Id.SIMPLE_NAME, property = "type")
+    sealed interface Payment permits Card, Upi {}
+    record Card(long amount) implements Payment {}
+    record Upi(long amount) implements Payment {}
+
+    // Control: the same shape without the word sealed.
+    @JsonTypeInfo(use = JsonTypeInfo.Id.SIMPLE_NAME, property = "type")
+    interface OpenPayment {}
+    record OpenCard(long amount) implements OpenPayment {}
+
+    static void tryRead(JsonMapper m, String label, String json, Class<?> type) {
+        try {
+            System.out.println(label + ": " + m.readValue(json, type));
+        } catch (Exception e) {
+            System.out.println(label + ": " + e.getClass().getSimpleName() + ": " + e.getMessage().lines().findFirst().orElse(""));
+        }
+    }
+
+    public static void main(String[] args) {
+        JsonMapper m = JsonMapper.builder().build();
+        System.out.println("write         : " + m.writeValueAsString(new Card(500)));
+        tryRead(m, "sealed, Card  ", "{\"type\":\"Card\",\"amount\":500}", Payment.class);
+        tryRead(m, "sealed, Upi   ", "{\"type\":\"Upi\",\"amount\":500}", Payment.class);
+        tryRead(m, "sealed, Cheque", "{\"type\":\"Cheque\",\"amount\":500}", Payment.class);
+        tryRead(m, "plain, OpenCard", "{\"type\":\"OpenCard\",\"amount\":500}", OpenPayment.class);
+    }
+}

sealed/jackson/JsonPayment.java

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+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(""));
+        }
+    }
+}

sealed/jackson/fetch.sh

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+#!/usr/bin/env bash
+# Downloads the three Jackson jars from Maven Central into ./lib and checks each against the published .sha1
+set -euo pipefail
+cd "$(dirname "$0")"; mkdir -p lib
+M=https://repo1.maven.org/maven2
+for a in tools/jackson/core/jackson-databind/3.2.3/jackson-databind-3.2.3 \
+         tools/jackson/core/jackson-core/3.2.3/jackson-core-3.2.3 \
+         com/fasterxml/jackson/core/jackson-annotations/2.22/jackson-annotations-2.22; do
+  f="lib/$(basename "$a").jar"
+  [ -f "$f" ] || curl -sfL -o "$f" "$M/$a.jar"
+  want="$(curl -sfL "$M/$a.jar.sha1" | cut -d' ' -f1)"; got="$(sha1sum "$f" | cut -d' ' -f1)"
+  [ "$want" = "$got" ] && echo "ok  $f  $got" || { echo "SHA1 MISMATCH $f"; exit 1; }
+done