java-server: Make AbstractApiJaxbJsonProvider more customisable in code

.changeset/pink-starfishes-turn.md

@@ -0,0 +1,7 @@
+---
+"@openapi-generator-plus/java-jaxrs-server-generator": minor
+---
+
+Make AbstractApiJaxbJsonProvider more customisable in code.
+
+Rather than relying on replacing a Handlebars frag.

packages/java-jaxrs-server/templates/AbstractApiJaxbJsonProvider.hbs

@@ -10,7 +10,37 @@ public abstract class AbstractApiJaxbJsonProvider extends com.fasterxml.jackson.
 	}
 
 	protected com.fasterxml.jackson.databind.ObjectMapper createMapper() {
-		{{>frag/jaxbJsonProviderBody}}
+		com.fasterxml.jackson.databind.ObjectMapper mapper = new com.fasterxml.jackson.databind.ObjectMapper();
+
+		/* We don't serialise null values so the client can treat them as null or undefined as they see fit */
+		mapper.setSerializationInclusion(com.fasterxml.jackson.annotation.JsonInclude.Include.NON_NULL);
+
+		/* Support PATCH requests using java.util.Optional */
+		if (isRegisterJdk8Module()) {
+			mapper.registerModule(createJdk8Module());
+		}
+
+		/* Support Java time object types */
+		mapper.registerModule(createJavaTimeModule());
+		mapper.configure(com.fasterxml.jackson.databind.SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, isWriteDatesAsTimestamps());
+
+		return mapper;
+	}
+
+	protected boolean isRegisterJdk8Module() {
+		return true;
+	}
+
+	protected com.fasterxml.jackson.datatype.jdk8.Jdk8Module createJdk8Module() {
+		return new com.fasterxml.jackson.datatype.jdk8.Jdk8Module();
+	}
+
+	protected com.fasterxml.jackson.datatype.jsr310.JavaTimeModule createJavaTimeModule() {
+		return new com.fasterxml.jackson.datatype.jsr310.JavaTimeModule();
+	} 
+
+	protected boolean isWriteDatesAsTimestamps() {
+		return false;
 	}
 
 }