What is the suggested way to modify / override / extend built-in Jackson 2 ObjectMapper in Spring Webflux? - spring

Question

Currently I have a minimalistic Spring / Netty, Reactor / Web Flux project with Jackson libraries
#Configuration
public class EmbeddedSpringServer extends DelegatingWebFluxConfiguration {
#Bean
MyController controller() {
return new AdminController();
}
public static void main(String[] args) throws Exception {
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(EmbeddedSpringServer.class);
HttpHandler handler = WebHttpHandlerBuilder.applicationContext(applicationContext).build();
ReactorHttpHandlerAdapter adapter = new ReactorHttpHandlerAdapter(handler);
HttpServer.create("0.0.0.0", 8082).newHandler(adapter).subscribe();
applicationContext.registerShutdownHook();
}
}
build.gradle:
compile 'org.springframework:spring-context:5.0.2.RELEASE'
compile 'org.springframework:spring-web:5.0.2.RELEASE'
compile 'org.springframework:spring-webflux:5.0.2.RELEASE'
compile 'io.projectreactor.ipc:reactor-netty:0.7.2.RELEASE'
compile group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: '2.9.3'
Controller class works fine (it returns a Mono<> with a DTO type).
Because Jackson is present in classpath Web Flux automatically creates an Object Mapper instance via DefaultServerCodecConfigurer however it's not clear how to override object mapper instance, because most Web Flux configuration classes are package private.
What I'd like to achieve is to create my own object mapper to add custom LocalDateTime serialization implemented in jackson-modules-java8
ObjectMapper mapper = new ObjectMapper()
.registerModule(new ParameterNamesModule())
.registerModule(new Jdk8Module())
.registerModule(new JavaTimeModule())
;
The problem is that's it's not clear how to modify Jackson2JsonEncoder created in package private org.springframework.http.codec.support.AbstractCodecConfigurer.AbstractDefaultCodecs.

Answer 1

You can disable that Jackson feature right from your application.properties file with:
spring.jackson.serialization.write-dates-as-timestamps=false

Answer 2

It turned out simpler than I thought initially as DelegatingWebFluxConfiguration already has a configureHttpMessageCodecs method overriding which is enough
#Configuration
public class EmbeddedSpringServer extends DelegatingWebFluxConfiguration {
#Bean
MyController controller() {
return new MyController();
}
public static void main(String[] args) throws Exception {
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(EmbeddedSpringServer.class);
HttpHandler handler = WebHttpHandlerBuilder.applicationContext(applicationContext).build();
ReactorHttpHandlerAdapter adapter = new ReactorHttpHandlerAdapter(handler);
HttpServer.create("0.0.0.0", 8082).newHandler(adapter).subscribe();
applicationContext.registerShutdownHook();
}
#Bean
ObjectMapper objectMapper(){
return new ObjectMapper()
.registerModule(new ParameterNamesModule())
.registerModule(new Jdk8Module())
.registerModule(new JavaTimeModule());
}
#Override
protected void configureHttpMessageCodecs(ServerCodecConfigurer configurer) {
configurer.defaultCodecs().jackson2JsonEncoder(new Jackson2JsonEncoder(objectMapper()));
configurer.defaultCodecs().jackson2JsonDecoder(new Jackson2JsonDecoder(objectMapper()));
}
}
as for the Spring Boot I think it can be also achieved by returning a webFluxConfigurer bean
#Bean
WebFluxConfigurer webFluxConfigurer(ObjectMapper objectMapper) {
return new WebFluxConfigurer() {
#Override
public void configureHttpMessageCodecs(ServerCodecConfigurer configurer) {
configurer.defaultCodecs().jackson2JsonEncoder(new Jackson2JsonEncoder(objectMapper());
configurer.defaultCodecs().jackson2JsonDecoder(new Jackson2JsonDecoder(objectMapper());
}
};
}
as they are picked by DelegatingWebFluxConfiguration created by #EnableWebFlux automatically.
N.B. default implementation of Jackson2ObjectMapperBuilder already registers these date modules automatically the problem with dates was not related, I ended with
#Override
protected void configureHttpMessageCodecs(ServerCodecConfigurer configurer) {
configurer.defaultCodecs().jackson2JsonEncoder(new Jackson2JsonEncoder(Jackson2ObjectMapperBuilder
.json()
.featuresToDisable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
.build()));
}
to achieve simple date serialization.