Project Structure Overview

Goals

To learn how to properly refactor to reactive

Step 1. From Bottom to Top

The goal of this step is to demonstrate how to start refactoring of the existing Microservices System in the way you will not break the whole system by introducing Reactive Programming concept with Project Reactor and WebFlux

The very first step you should start with is adding the

    implementation 'org.springframework.boot:spring-boot-starter-webflux'

dependency in all the places you have web module. This will keep WebMVC module as a priority one but will add support for Reactive Types and WebClient

1.1 Rework AuthenticationClient in the GatewayService

Modify HttpAuthenticationService to use WebClient

Remember. The API should remain imperative on this Step. Use method .block() to convert Reactive to Imperative

Run ServiceIntegrationTest to ensure functionality has not been broken during the modification

1.2 Add similar Authentication Request Customizer for WebClient

At the moment we have delivery.app.common.security.web.client.JWTHeadersClientRequestCustomizer responsible for adding Authorization: Bearer ... header to a request. If we replace RestTemplate , we need to make sure WebClient offers same functionality. For that purpose use org.springframework.web.reactive.function.client.ExchangeFilterFunction which is a new intercepting mechanism for WebClient and implement same logic was before.

Note: in new Reactive Web networking ClientRequest is an immutable entity. Use ClientRequest.from(origin)....build() to modify it in ExchengeFilterFunction.

Finally, modify the BaseConfiguration class, and define a WebClientCustomizer bean to introduce created ExchengeFilterFunction.

1.3 Start from simple. Rework HttpCatalogService in CartService

The simples Http integration which uses Auth functionality is in CartService rework it to WebClient support.

Remember. The API should remain imperative on this Step. Use method .block() to convert Reactive to Imperative

1.4 Rework UserService to use ReactiveCrudRepository with R2DBC

Add R2dbc support by replacing

implementation 'org.springframework.boot:spring-boot-starter-data-jdbc'

with

implementation 'org.springframework.boot:spring-boot-starter-data-r2dbc'
implementation("io.r2dbc:r2dbc-h2")

Also, make sure your are modifying application.yaml and adding replacing old datasource config:

spring:
  datasource:
    url: jdbc:h2:file:./build/data/usersdb
    driverClassName: org.h2.Driver
    username: sa
    password: password

with a new one:

spring:
   r2dbc:
      url: r2dbc:h2:file:///./build/data/usersdb
      username: sa
      password: password

Remember. The API should remain imperative on this Step. Use method .block() to convert Reactive to Imperative

Step 2. To WebFlux where it is needed!

At this step we will refactor completely to WebFlux but at the places where it is really needed!

Step 2.1 Refactor Gateway to WebFlux

1. Remove WebMVC dependency from the service

   Note: module commons may still bring an old WebMVC dependency. Exclude it from gateway-service/build.gradle using

     configurations.implementation  {
        exclude group: 'org.springframework.boot', module: 'spring-boot-starter-web'
     } 

2. Rework Security Configuration to Support WebFlux Security. Replace the old SecurityConfig with the following one

   @EnableWebFluxSecurity
   public class SecurityConfig {
   
     @Bean
     SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
       http
           .authorizeExchange((exchanges) ->
               exchanges
                   .pathMatchers("/login").permitAll()
                   .pathMatchers("/css/**", "/index").permitAll()
                   .pathMatchers(HttpMethod.GET, "/api/products", "/api/products/*").permitAll()
                   .anyExchange().authenticated()
           )
           .formLogin((formLogin) ->
               formLogin
                   .loginPage("/login")
           );
       return http.build();
     }
   }

3. Rebase RemoteAuthenticationManger to extend ReactiveAuthenticationManager
4. Migrate RoutingController to use Reactive Types from end to end. Use DataBuffer class instead of Resource

      public Mono<ResponseEntity<Flux<DataBuffer>>> handle(
          @PathVariable("service") String service, 
          @Nullable @PathVariable(value = "path", required = false) String path,
          HttpEntity<Flux<DataBuffer>> httpEntity, 
          HttpMethod httpMethod
      ) {
        // new impl
      }