feat: add subtype module (2.17) #229

black-06 · 2023-11-11T06:55:55Z

Adds a module that allows subtype to be registered without annotating the parent class.

It is implemented on SPI.

Its original version is https://github.com/black-06/jackson-modules-dynamic-subtype.

I removed the custom ServiceLoader and always use the standard library,
which means that pojo always needs a no-parameter constructor.

cowtowncoder · 2023-11-12T04:37:09Z

pom.xml

@@ -33,6 +33,7 @@ not datatype, data format, or JAX-RS provider modules.
    <module>mrbean</module>
    <module>osgi</module>
    <module>paranamer</module>
+    <module>subtype</module>


I'll probably want to change the name, "subtype" is too generic. But let me think about better name for a while...

It's a difficult thing for me to give it a name...

True🥲🥲

subtype/README.md

subtype/src/test/java/com/fasterxml/jackson/module/subtype/WithJsonSubTypesTest.java

cowtowncoder · 2023-11-12T04:48:10Z

subtype/src/test/java/com/fasterxml/jackson/module/subtype/WithoutJsonSubTypesTest.java

+import static org.junit.Assert.assertTrue;
+
+/**
+ * test work without {@link JsonSubTypes}


I am not sure I understand -- why would we test functioning without module? And isn't module actually register with the mapper. Or what is being tested here? Could probably use longer explanation of reasoning.

Probably test against Jackson polymorphic type handling working as expected. If so, does not seem necessary

I actually wanted to test whether @JsonSubType worked with @JsonSubTypes

JooHyukKim · 2023-11-12T05:02:18Z

subtype/src/main/java/com/fasterxml/jackson/module/subtype/SubtypeModule.java

+                List<NamedType> list1 = SubtypeModule.findSubtypes(a.getRawType(), a::getAnnotation);
+                List<NamedType> list2 = subtypes.getOrDefault(a.getRawType(), Collections.emptyList());


Can we rename these list1 and list2 to something less generic?

Here is a simple modification of https://github.com/FasterXML/jackson-databind/blob/3a271be870821301f73054e43e32f657e4753234/src/main/java/com/fasterxml/jackson/databind/introspect/AnnotationIntrospectorPair.java#L280-L291

JooHyukKim · 2023-11-12T05:05:14Z

subtype/src/main/java/com/fasterxml/jackson/module/subtype/SubtypeModule.java

+                if (list1.isEmpty()) return list2;
+                if (list2.isEmpty()) return list1;


If the two lists are null-safe, no need for empty checking.

JooHyukKim · 2023-11-12T05:05:28Z

subtype/src/main/java/com/fasterxml/jackson/module/subtype/SubtypeModule.java

+                List<NamedType> list = new ArrayList<>(list1.size() + list2.size());
+                list.addAll(list1);
+                list.addAll(list2);
+                return list;


Suggested change

List<NamedType> list = new ArrayList<>(list1.size() + list2.size());

list.addAll(list1);

list.addAll(list2);

return list;

List<NamedType> list = new ArrayList<>(list1.size() + list2.size());

list1.addAll(list2);

return list;

JooHyukKim · 2023-11-12T05:07:00Z

subtype/src/main/java/com/fasterxml/jackson/module/subtype/SubtypeModule.java

+                List<NamedType> list = new ArrayList<>(list1.size() + list2.size());
+                list.addAll(list1);
+                list.addAll(list2);
+                return list;


Is it possible to have duplication? If so, can we have these as set first, then return as list?

JooHyukKim · 2023-11-12T05:09:12Z

subtype/src/test/java/com/fasterxml/jackson/module/subtype/WithoutJsonSubTypesTest.java

+import static org.junit.Assert.assertTrue;
+
+/**
+ * test work without {@link JsonSubTypes}


Probably test against Jackson polymorphic type handling working as expected. If so, does not seem necessary

JooHyukKim · 2023-11-12T05:10:35Z

subtype/src/main/java/com/fasterxml/jackson/module/subtype/SubtypeModule.java

+        subtypes.remove(parent);
+    }
+
+    private static <S> List<NamedType> findSubtypes(Class<S> clazz, Function<Class<JsonSubType>, JsonSubType> getter) {


Is there a reason for keeping it static? if not maybe like...

Suggested change

private static <S> List<NamedType> findSubtypes(Class<S> clazz, Function<Class<JsonSubType>, JsonSubType> getter) {

private <S> List<NamedType> _findSubtypes(Class<S> clazz, Function<Class<JsonSubType>, JsonSubType> getter) {

JooHyukKim · 2023-11-12T05:13:57Z

subtype/src/main/java/com/fasterxml/jackson/module/subtype/JsonSubType.java

+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+@JacksonAnnotation
+public @interface JsonSubType {


Name sounds like it's part of @JsonSubTypes of annotations module. This may confuse users quite. If module name changes as per https://github.com/FasterXML/jackson-modules-base/pull/229/files#r1390329649, can we change name here also?

JooHyukKim · 2023-11-12T05:14:35Z

subtype/src/main/java/com/fasterxml/jackson/module/subtype/JsonSubType.java

+     * more than one type name should be associated with the same type.
+     *
+     * @return subtype name array
+     * @since 2.12


Version mismatch, can remove.

Suggested change

* @since 2.12

... then add @since 2.16 to the class

JooHyukKim · 2023-11-12T05:15:20Z

subtype/src/main/java/com/fasterxml/jackson/module/subtype/SubtypeModule.java

+ * Therefore, we can {@link #unregisterType} a class and then module will reload this class's subclasses.
+ */
+public class SubtypeModule extends Module {


Suggested change

* Therefore, we can {@link #unregisterType} a class and then module will reload this class's subclasses.

*/

public class SubtypeModule extends Module {

* Therefore, we can {@link #unregisterType} a class and then module will reload this class's subclasses.

*

* @since 2.16

*/

public class SubtypeModule extends Module {

cowtowncoder · 2023-11-16T02:24:18Z

Quick note: due to timing, decided that I will not try to get this in Jackson 2.16 -- so will need to be re-based to 2.17.
This because there's a bit of work to be done here.

For example, I think that naming of @JsonSubType should change as the general rule is that only jackson-annotations has annotations with name starting with @Json (and for legacy reasons, some in jackson-databind).
Modules can provide annotations that start with @Jackson prefix (or anything else that makes sense).

But I need to read the PR in bit more thought to make sure my feedback is relevant.

amricko0b · 2025-09-03T13:06:00Z

Hello everyone!
Any updates on this one?

cowtowncoder · 2025-09-03T14:04:19Z

I totally forgot. If this was to be added, would need to re-base/re-create against 2.x branch.

black-06 · 2025-09-04T01:11:17Z

I totally forgot. If this was to be added, would need to re-base/re-create against 2.x branch.

I've changed base to 2.x branch, and I checked the comments above, most of them have been modified, and the problems that haven't been solved include:

findSubtypes: It's almost a copy of AnnotationIntrospectorPair.findSubtypes, so I tend not to modify it.
annotation name JsonSubType: If the user understands JsonSubTypes, then he should be able to understand JsonSubType easily, but if there is a more appropriate name, I have no problem.

Because it's been a while. We can review the code again.

feat: add subtype module

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black-06 mentioned this pull request Nov 11, 2023

Contribute to jackson-modules-base black-06/jackson-modules-dynamic-subtype#1

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fix

5152c26

cowtowncoder changed the title ~~feat: add subtype module~~ feat: add subtype module (2.17) Nov 16, 2023

cowtowncoder added the 2.17 label Nov 16, 2023

black-06 added 4 commits September 4, 2025 08:44

Merge branch 'FasterXML:2.x' into subtype

ec05795

feat: add subtype module

57009d8

fix

e9ee005

Merge remote-tracking branch 'origin/subtype' into subtype

f7f0cb6

black-06 changed the base branch from 2.16 to 2.x September 4, 2025 00:57

		List<NamedType> list1 = SubtypeModule.findSubtypes(a.getRawType(), a::getAnnotation);
		List<NamedType> list2 = subtypes.getOrDefault(a.getRawType(), Collections.emptyList());

		if (list1.isEmpty()) return list2;
		if (list2.isEmpty()) return list1;

	private static <S> List<NamedType> findSubtypes(Class<S> clazz, Function<Class<JsonSubType>, JsonSubType> getter) {
	private <S> List<NamedType> _findSubtypes(Class<S> clazz, Function<Class<JsonSubType>, JsonSubType> getter) {

feat: add subtype module (2.17) #229

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black-06 commented Nov 11, 2023

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cowtowncoder commented Nov 16, 2023

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amricko0b commented Sep 3, 2025

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cowtowncoder commented Sep 3, 2025

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black-06 commented Sep 4, 2025

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