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Test a class-level @JsonbTypeSerializer inside a collection and
directly, in that order. ComponentMatcher already finds such a
serializer since #689, so take only an adapter from the customization
of the runtime class, and keep the customization of the declared type
when it binds a serializer or an adapter.

Signed-off-by: Sharang Gupta <sharang@sharanggupta.dev>

src/main/java/org/eclipse/yasson/internal/serializer/SerializationModelCreator.java

diff --git a/src/main/java/org/eclipse/yasson/internal/serializer/SerializationModelCreator.java b/src/main/java/org/eclipse/yasson/internal/serializer/SerializationModelCreator.java
index b42d947..cb49652 100644
--- a/src/main/java/org/eclipse/yasson/internal/serializer/SerializationModelCreator.java
+++ b/src/main/java/org/eclipse/yasson/internal/serializer/SerializationModelCreator.java
@@ -124,27 +124,25 @@
     /**
      * Return the customization to create the serializer of a type only known at runtime with.
      * The given customization is the one of the declared type, for example {@link Object} for the elements of a raw
-     * collection, so a serializer or an adapter bound to the class of the runtime type, for example with
-     * {@code @JsonbTypeAdapter} on the class, is taken from the customization of that class when the given
-     * customization does not bind one.
+     * collection, so an adapter bound to the class of the runtime type with {@code @JsonbTypeAdapter} is taken from
+     * the customization of that class when the given customization binds neither a serializer nor an adapter.
+     * A serializer bound to the class with {@code @JsonbTypeSerializer} is already found by
+     * {@link ComponentMatcher#getSerializerBinding}.
      *
      * @param runtimeType   runtime type of the value
      * @param customization customization of the declared type
      * @return customization to use
      */
     private Customization runtimeTypeCustomization(Class<?> runtimeType, Customization customization) {
-        if (bindsSerializationComponent((ComponentBoundCustomization) customization)) {
+        ComponentBoundCustomization declared = (ComponentBoundCustomization) customization;
+        if (declared != null
+                && (declared.getSerializerBinding() != null || declared.getSerializeAdapterBinding() != null)) {
             return customization;
         }
         ClassCustomization classCustomization = jsonbContext.getMappingContext()
                 .getOrCreateClassModel(runtimeType)
                 .getClassCustomization();
-        return bindsSerializationComponent(classCustomization) ? classCustomization : customization;
-    }
-
-    private static boolean bindsSerializationComponent(ComponentBoundCustomization customization) {
-        return customization != null
-                && (customization.getSerializerBinding() != null || customization.getSerializeAdapterBinding() != null);
+        return classCustomization.getSerializeAdapterBinding() != null ? classCustomization : customization;
     }
 
     private ModelSerializer serializerChain(LinkedList<Type> chain,

src/test/java/org/eclipse/yasson/adapters/JsonbTypeAdapterTest.java

diff --git a/src/test/java/org/eclipse/yasson/adapters/JsonbTypeAdapterTest.java b/src/test/java/org/eclipse/yasson/adapters/JsonbTypeAdapterTest.java
index 0440178..4bfb142 100644
--- a/src/test/java/org/eclipse/yasson/adapters/JsonbTypeAdapterTest.java
+++ b/src/test/java/org/eclipse/yasson/adapters/JsonbTypeAdapterTest.java
@@ -152,6 +152,7 @@
 
     @Test
     public void testClassAdapterOfCollectionElement() throws Exception {
+        // Must use a new Jsonb instance to make sure adapter cache is empty
         try (Jsonb jsonb = JsonbBuilder.create()) {
             assertEquals("[\"adapted\"]", jsonb.toJson(List.of(new AnnotatedType())));
             assertEquals("\"adapted\"", jsonb.toJson(new AnnotatedType()));

src/test/java/org/eclipse/yasson/serializers/SerializersTest.java

diff --git a/src/test/java/org/eclipse/yasson/serializers/SerializersTest.java b/src/test/java/org/eclipse/yasson/serializers/SerializersTest.java
index 8214b88..26a829a 100644
--- a/src/test/java/org/eclipse/yasson/serializers/SerializersTest.java
+++ b/src/test/java/org/eclipse/yasson/serializers/SerializersTest.java
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2016, 2025 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v. 2.0 which is available at
@@ -839,6 +840,27 @@
 
     }
 
+    @JsonbTypeSerializer(SerializedTypeSerializer.class)
+    public static class SerializedType {
+        public String field = "value";
+    }
+
+    public static class SerializedTypeSerializer implements JsonbSerializer<SerializedType> {
+        @Override
+        public void serialize(SerializedType obj, JsonGenerator generator, SerializationContext ctx) {
+            generator.write("serialized");
+        }
+    }
+
+    @Test
+    public void testClassSerializerOfCollectionElement() throws Exception {
+        // Must use a new Jsonb instance to make sure serializer cache is empty
+        try (Jsonb jsonb = JsonbBuilder.create()) {
+            assertEquals("[\"serialized\"]", jsonb.toJson(List.of(new SerializedType())));
+            assertEquals("\"serialized\"", jsonb.toJson(new SerializedType()));
+        }
+    }
+
     /**
      * Test that annotation-based serializers work when property is declared as Object
      * but the runtime type has @JsonbTypeSerializer annotation.