Add Jackson2/3 to custom object mapper sections in docs.

spring-pulsar-docs/src/main/antora/modules/ROOT/pages/attributes/attributes-variables.adoc

@@ -9,8 +9,8 @@
 :github: https://github.com/spring-projects/spring-pulsar
 :javadocs: https://docs.spring.io/spring-pulsar/docs/{spring-pulsar-version}/api
 :spring-framework-docs: https://spring.io/projects/spring-framework#learn
-:spring-boot-docs: https://docs.spring.io/spring-boot/docs/{spring-boot-version}/reference/htmlsingle
-:spring-boot-pulsar-config-props: {spring-boot-docs}/#application-properties.integration
+:spring-boot-docs: https://docs.spring.io/spring-boot/{spring-boot-version}
+:spring-boot-pulsar-config-props: {spring-boot-docs}/appendix/application-properties/index.html#appendix.application-properties.integration
 :spring-cloud-stream-docs: https://docs.spring.io/spring-cloud-stream/docs/{spring-cloud-stream-version}/reference/html/
 :spring-cloud-function: https://spring.io/projects/spring-cloud-function
 

spring-pulsar-docs/src/main/antora/modules/ROOT/pages/reference/custom-object-mapper.adoc

@@ -1,9 +1,9 @@
 [[custom-object-mapper]]
 = Custom Object Mapper
-include::../attributes/attributes.adoc[]
+include::../attributes/attributes-variables.adoc[]
 
-Pulsar uses an internal Jackson `ObjectMapper` when de/serializing JSON messages.
-If you instead want to provide your own object mapper instance, you can register a `SchemaResolverCustomizer` and set your mapper on the `DefaultSchemaResolver` as follows:
+Pulsar uses an internal shaded Jackson `ObjectMapper` when de/serializing JSON messages.
+If you instead want to provide your own Jackson 2 object mapper instance, you can register a `SchemaResolverCustomizer` and set your mapper on the `DefaultSchemaResolver` as follows:
 
 [source,java,indent=0,subs="verbatim"]
 ----
@@ -16,6 +16,8 @@ SchemaResolverCustomizer<DefaultSchemaResolver> schemaResolverCustomizer() {
 }
 ----
 
+IMPORTANT: The object mapper in the example above should be an instance of `com.fasterxml.jackson.databind.ObjectMapper`, **not** the shaded `org.apache.pulsar.shade.com.fasterxml.jackson.databind.ObjectMapper`.
+
 This results in your object mapper being used to de/serialize all JSON messages that go through the schema resolution process (i.e. in cases where you do not pass a schema in directly when producing/consuming messages).
 
 Under the hood, the resolver creates a special JSON schema which leverages the custom mapper and is used as the schema for all resolved JSON messages.
@@ -46,3 +48,13 @@ myObjectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
 
 ====
 NOTE: A later version of the framework may instead provide a customizer that operates on the default mapper rather than requiring a separate instance.
+
+[[jackson2vs3]]
+== Jackson 2 / Jackson 3
+In Spring Boot 4 the default version of {spring-boot-docs}/reference/features/json.html#features.json.jackson[Jackson is 3] and is auto-configured via the spring-boot-starter-json module.
+However, Spring for Apache Pulsar expects a {spring-boot-docs}/reference/features/json.html#features.json.jackson2[Jackson 2] custom mapper.
+
+If you are using Jackson 3 in your Spring Boot 4 application and want to use a custom mapper you will need to add Jackson 2 to the classpath.
+Don't worry, Spring Boot 4 allows Jackson 2 and 3 to co-exist in an application.
+
+NOTE: A later version of the framework may support using a Jackson 2 or Jackson 3 custom mapper.

spring-pulsar-docs/src/main/antora/modules/ROOT/pages/reference/pulsar-header.adoc

@@ -44,7 +44,7 @@ During inbound mapping, they are mapped as `String`.
 By default, only `org.springframework.util.MimeType` and `org.springframework.http.MediaType` are mapped this way.
 
 ===== Custom ObjectMapper
-The JSON mapper uses a reasonable configured Jasckson `ObjectMapper` to handle serialization of header values.
+The JSON mapper uses a reasonable configured Jackson 2 `ObjectMapper` to handle serialization of header values.
 However, to provide a custom object mapper one must simply provide an `ObjectMapper` bean with the name `pulsarHeaderObjectMapper`.
 For example:
 [source, java]
@@ -61,6 +61,10 @@ static class PulsarHeadersCustomObjectMapperTestConfig {
 }
 ----
 
+IMPORTANT: The object mapper in the example above should be an instance of `com.fasterxml.jackson.databind.ObjectMapper`, **not** the shaded `org.apache.pulsar.shade.com.fasterxml.jackson.databind.ObjectMapper`.
+
+IMPORTANT: The xref:reference/custom-object-mapper.adoc#jackson2vs3[same limitations] regarding Jackson 2 vs. Jackson 3 apply here }
+
 === Inbound/Outbound Patterns
 On the inbound side, by default, all Pulsar headers (message metadata plus user properties) are mapped to `MessageHeaders`.
 On the outbound side, by default, all `MessageHeaders` are mapped, except `id`, `timestamp`, and the headers that represent the Pulsar message metadata (i.e. the headers that are prefixed with `pulsar_message_`).