part4custom: add E06 (ValueDeserializer direct) and E07 (mix-in on a record), fix run-all.sh exit-code detection through the grep filter (post #50)
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@@ -9,7 +9,7 @@ nothing is transcribed by hand.
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```
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Jackson 3.2.3 (tools.jackson.core:jackson-databind)
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jackson-annotations 2.22 (com.fasterxml.jackson.core — deliberately unchanged)
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JDK Temurin 21.0.5
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JDK Temurin 25.0.4.1 (LTS)
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Maven 3.9.9
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```
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@@ -18,7 +18,7 @@ Maven 3.9.9
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```bash
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git clone https://ankurm.com/git.app/asmhatre/jackson3-by-example.git
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cd jackson3-by-example
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./run-all.sh # compiles, runs all 37 examples, refreshes docs/output/
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./run-all.sh # compiles, runs all 39 examples, refreshes docs/output/
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```
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Or run any single example:
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@@ -36,7 +36,7 @@ mvn -q exec:java -Dexec.mainClass=com.ankurm.jackson3.part5polymorphic.F01Serial
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| [ObjectMapper Guide](https://ankurm.com/jackson-objectmapper-guide/) | [`part1objectmapper`](src/main/java/com/ankurm/jackson3/part1objectmapper) | [B01](src/main/java/com/ankurm/jackson3/part1objectmapper/B01WriteJson.java) [B02](src/main/java/com/ankurm/jackson3/part1objectmapper/B02ReadJson.java) [B03](src/main/java/com/ankurm/jackson3/part1objectmapper/B03GenericCollections.java) [B04](src/main/java/com/ankurm/jackson3/part1objectmapper/B04PropertyOrdering.java) | [write-up](docs/part1-objectmapper.md) |
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| [Records, Optionals, Sealed](https://ankurm.com/jackson-java-records-optionals/) | [`part2modernjava`](src/main/java/com/ankurm/jackson3/part2modernjava) | [C01](src/main/java/com/ankurm/jackson3/part2modernjava/C01RecordRoundTrip.java) [C02](src/main/java/com/ankurm/jackson3/part2modernjava/C02OptionalFields.java) [C03](src/main/java/com/ankurm/jackson3/part2modernjava/C03SealedWithSubTypes.java) [C04](src/main/java/com/ankurm/jackson3/part2modernjava/C04SealedAutoDiscovery.java) | [write-up](docs/part2-modern-java.md) |
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| [Annotations Cheat Sheet](https://ankurm.com/jackson-annotations-guide/) | [`part3annotations`](src/main/java/com/ankurm/jackson3/part3annotations) | [D01](src/main/java/com/ankurm/jackson3/part3annotations/D01RenameAndIgnore.java) [D02](src/main/java/com/ankurm/jackson3/part3annotations/D02InclusionAndFormat.java) [D03](src/main/java/com/ankurm/jackson3/part3annotations/D03AliasAndUnknownFields.java) [D04](src/main/java/com/ankurm/jackson3/part3annotations/D04CreatorsAndUnwrapping.java) | [write-up](docs/part3-annotations.md) |
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| [Custom Serialisers & Mix-ins](https://ankurm.com/jackson-custom-serializer-mixin/) | [`part4custom`](src/main/java/com/ankurm/jackson3/part4custom) | [E01](src/main/java/com/ankurm/jackson3/part4custom/E01MoneyValueSerializer.java) [E02](src/main/java/com/ankurm/jackson3/part4custom/E02MoneyValueDeserializer.java) [E03](src/main/java/com/ankurm/jackson3/part4custom/E03SimpleModuleRegistration.java) [E04](src/main/java/com/ankurm/jackson3/part4custom/E04MixinAnnotations.java) [E05](src/main/java/com/ankurm/jackson3/part4custom/E05ValueSerializerDirect.java) | [write-up](docs/part4-custom.md) |
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| [Custom Serialisers & Mix-ins](https://ankurm.com/jackson-custom-serializer-mixin/) | [`part4custom`](src/main/java/com/ankurm/jackson3/part4custom) | [E01](src/main/java/com/ankurm/jackson3/part4custom/E01MoneyValueSerializer.java) [E02](src/main/java/com/ankurm/jackson3/part4custom/E02MoneyValueDeserializer.java) [E03](src/main/java/com/ankurm/jackson3/part4custom/E03SimpleModuleRegistration.java) [E04](src/main/java/com/ankurm/jackson3/part4custom/E04MixinAnnotations.java) [E05](src/main/java/com/ankurm/jackson3/part4custom/E05ValueSerializerDirect.java) [E06](src/main/java/com/ankurm/jackson3/part4custom/E06ValueDeserializerDirect.java) [E07](src/main/java/com/ankurm/jackson3/part4custom/E07MixinOnRecord.java) | [write-up](docs/part4-custom.md) (now superseded by the rewritten post itself — see below) |
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| [Polymorphic Deserialisation](https://ankurm.com/jackson-polymorphic-deserialization/) | [`part5polymorphic`](src/main/java/com/ankurm/jackson3/part5polymorphic) | [F01](src/main/java/com/ankurm/jackson3/part5polymorphic/F01SerialiseMixedList.java) [F02](src/main/java/com/ankurm/jackson3/part5polymorphic/F02DeserialiseMixedList.java) [F03](src/main/java/com/ankurm/jackson3/part5polymorphic/F03IncludeStrategies.java) [F04](src/main/java/com/ankurm/jackson3/part5polymorphic/F04UnknownTypeId.java) | [write-up](docs/part5-polymorphic.md) |
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| [Streaming API & JsonNode](https://ankurm.com/jackson-streaming-api-jsonnode/) | [`part6streaming`](src/main/java/com/ankurm/jackson3/part6streaming) | [G01](src/main/java/com/ankurm/jackson3/part6streaming/G01StreamingParserFilter.java) [G02](src/main/java/com/ankurm/jackson3/part6streaming/G02StreamingGenerator.java) [G03](src/main/java/com/ankurm/jackson3/part6streaming/G03TreeModelNavigation.java) [G04](src/main/java/com/ankurm/jackson3/part6streaming/G04ThreeApproachesMeasured.java) | [write-up](docs/part6-streaming.md) |
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| [Security Best Practices](https://ankurm.com/jackson-security-best-practices/) | [`part7security`](src/main/java/com/ankurm/jackson3/part7security) | [H01](src/main/java/com/ankurm/jackson3/part7security/H01SafePolymorphismByAnnotation.java) [H02](src/main/java/com/ankurm/jackson3/part7security/H02DefaultTypingRemoved.java) [H03](src/main/java/com/ankurm/jackson3/part7security/H03PolymorphicTypeValidatorAllowlist.java) [H04](src/main/java/com/ankurm/jackson3/part7security/H04StreamReadConstraints.java) [H05](src/main/java/com/ankurm/jackson3/part7security/H05NeverDeserialiseIntoObject.java) | [write-up](docs/part7-security.md) |
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@@ -53,13 +53,13 @@ the library disagree.
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| [docs/part1-objectmapper.md](docs/part1-objectmapper.md) | Reading, writing, `TypeReference`, property ordering |
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| [docs/part2-modern-java.md](docs/part2-modern-java.md) | Records, `Optional`, sealed types and auto-discovery |
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| [docs/part3-annotations.md](docs/part3-annotations.md) | The annotation set, and which advice is now obsolete |
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| [docs/part4-custom.md](docs/part4-custom.md) | `ValueSerializer`, `ValueDeserializer`, modules, mix-ins |
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| [docs/part4-custom.md](docs/part4-custom.md) | `ValueSerializer`, `ValueDeserializer`, modules, mix-ins — superseded by the rewritten post's own in-page depth; kept here for history, not extended further |
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| [docs/part5-polymorphic.md](docs/part5-polymorphic.md) | `@JsonTypeInfo`, and the dropped-discriminator defect in full |
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| [docs/part6-streaming.md](docs/part6-streaming.md) | Streaming, the tree model, and the three approaches measured |
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| [docs/part7-security.md](docs/part7-security.md) | Safe polymorphism, allowlists, resource limits |
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| [docs/beyond.md](docs/beyond.md) | Unchecked exceptions, flipped defaults, pool tuning |
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Raw stdout for all 37 programs is in [`docs/output/`](docs/output), regenerated by
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Raw stdout for all 39 programs is in [`docs/output/`](docs/output), regenerated by
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[`run-all.sh`](run-all.sh).
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## Corrections to the posts
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@@ -90,6 +90,11 @@ Two smaller ones worth knowing, neither strictly an error in the posts:
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- `{"amount":20.00}` deserialises to `BigDecimal` **20.0**, not 20.00 — the scale is lost
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unless `USE_BIG_DECIMAL_FOR_FLOATS` is enabled. See
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[E03](src/main/java/com/ankurm/jackson3/part4custom/E03SimpleModuleRegistration.java).
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- `addMixIn()` works on a `record`, not just a field-and-getter class — but the mix-in has
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to declare methods named like the record's own accessors (`postalCode()`), not
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getter-style names (`getPostalCode()`), because that is what a record's introspected
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properties are actually called. See
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[E07](src/main/java/com/ankurm/jackson3/part4custom/E07MixinOnRecord.java).
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## Measured, not asserted
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@@ -0,0 +1,4 @@
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serialised : {"assignee":"u-42","title":"Fix build"}
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round-trip : Ticket[assignee=UserId[value=u-42], title=Fix build]
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equal : true
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no module : MismatchedInputException - Cannot construct instance of `com.ankurm.jackson3.part4custom.E06ValueDeserializerDirect$UserId` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('u-42')
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@@ -0,0 +1,2 @@
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with mixin : {"street":"123 Main St","city":"Springfield","zip":"12345"}
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without mixin: {"street":"123 Main St","city":"Springfield","postalCode":"12345","internalTrackingCode":"INTERNAL-X99"}
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+5
-1
@@ -15,7 +15,11 @@ for f in $(find src/main/java -name '*.java' | sort); do
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grep -q 'public static void main' "$f" || continue
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SHORT="${CLASS##*.}"
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printf '%-52s' "$SHORT"
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if java -cp "$CP" "$CLASS" > "docs/output/$SHORT.txt" 2>&1; then
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# grep -v strips the sandbox's injected "Picked up JAVA_TOOL_OPTIONS" proxy-config
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# notice from stderr - it is an artifact of this environment, not program output.
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# PIPESTATUS[0] (not grep's own exit code) is what tells us whether java itself failed.
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java -cp "$CP" "$CLASS" 2>&1 | grep -v '^Picked up JAVA_TOOL_OPTIONS' > "docs/output/$SHORT.txt"
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if [ "${PIPESTATUS[0]}" -eq 0 ]; then
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echo "ok"
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else
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echo "FAILED"; FAILED=1
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@@ -0,0 +1,65 @@
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package com.ankurm.jackson3.part4custom;
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import tools.jackson.core.JsonParser;
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import tools.jackson.databind.DeserializationContext;
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import tools.jackson.databind.ValueDeserializer;
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import tools.jackson.databind.json.JsonMapper;
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import tools.jackson.databind.module.SimpleModule;
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/**
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* BEYOND THE POST — the deserialising half of E05ValueSerializerDirect.
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*
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* E05 showed ValueSerializer<T> written directly, without the StdSerializer detour.
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* This is the other half: ValueDeserializer<T> written directly, without StdDeserializer.
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* Together they round-trip UserId as a bare JSON string ("u-42") instead of the
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* structural {"value":"u-42"} a record would otherwise produce.
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*/
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public class E06ValueDeserializerDirect {
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public record UserId(String value) { }
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static class UserIdSerializer extends tools.jackson.databind.ValueSerializer<UserId> {
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@Override
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public void serialize(UserId id, tools.jackson.core.JsonGenerator gen,
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tools.jackson.databind.SerializationContext ctxt) {
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gen.writeString(id.value());
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}
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}
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/** Reads the bare JSON string straight back into the wrapper type. */
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static class UserIdDeserializer extends ValueDeserializer<UserId> {
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@Override
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public UserId deserialize(JsonParser p, DeserializationContext ctxt) {
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return new UserId(p.getString());
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}
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}
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public record Ticket(UserId assignee, String title) { }
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public static void main(String[] args) {
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SimpleModule module = new SimpleModule("UserIdModule");
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module.addSerializer(UserId.class, new UserIdSerializer());
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module.addDeserializer(UserId.class, new UserIdDeserializer());
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JsonMapper mapper = JsonMapper.builder().addModule(module).build();
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Ticket original = new Ticket(new UserId("u-42"), "Fix build");
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String json = mapper.writeValueAsString(original);
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System.out.println("serialised : " + json);
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Ticket restored = mapper.readValue(json, Ticket.class);
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System.out.println("round-trip : " + restored);
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System.out.println("equal : " + original.equals(restored));
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// Without the module, Jackson can't turn a bare JSON string "u-42" into a
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// one-component record - it expects {"value":"u-42"} and this throws.
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JsonMapper plain = JsonMapper.builder().build();
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try {
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plain.readValue("{\"assignee\":\"u-42\",\"title\":\"Fix build\"}", Ticket.class);
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System.out.println("no module : (unexpectedly succeeded)");
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} catch (Exception e) {
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System.out.println("no module : " + e.getClass().getSimpleName()
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+ " - " + e.getMessage().lines().findFirst().orElse(""));
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}
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}
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}
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@@ -0,0 +1,44 @@
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package com.ankurm.jackson3.part4custom;
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import com.fasterxml.jackson.annotation.JsonIgnore;
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import com.fasterxml.jackson.annotation.JsonProperty;
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import tools.jackson.databind.json.JsonMapper;
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/**
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* BEYOND THE POST — does addMixIn() still work when the third-party type is a
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* record, not a field-and-getter class like E04's Address?
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*
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* A record's "properties" are its canonical accessor methods (postalCode(), not
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* getPostalCode()), so a mixin has to declare methods with those exact names for
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* Jackson's annotation-introspection merge to find them. Run this before assuming
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* either way - the answer below was obtained by actually running it, not inferred
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* from how E04's field-based mixin behaves.
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*/
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public class E07MixinOnRecord {
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/** Stand-in for a third-party record type whose source you cannot modify. */
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public record AddressRecord(String street, String city, String postalCode,
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String internalTrackingCode) { }
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/** Mix-in for AddressRecord: method signatures, not fields, to match a record's accessors. */
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public interface AddressRecordMixin {
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@JsonIgnore
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String internalTrackingCode();
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@JsonProperty("zip")
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String postalCode();
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}
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public static void main(String[] args) {
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AddressRecord address = new AddressRecord(
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"123 Main St", "Springfield", "12345", "INTERNAL-X99");
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JsonMapper withMixin = JsonMapper.builder()
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.addMixIn(AddressRecord.class, AddressRecordMixin.class)
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.build();
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System.out.println("with mixin : " + withMixin.writeValueAsString(address));
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JsonMapper withoutMixin = JsonMapper.builder().build();
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System.out.println("without mixin: " + withoutMixin.writeValueAsString(address));
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}
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}
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