Spring Boot RouterFunction

last modified July 29, 2023

In this article we show how to create functional routes in Spring Boot applications.

Reactive programming

Reactive programming is a programming paradigm that is functional, event-based, non-blocking, asynchronous, and centered around data stream processing. The term reactive comes from the fact that we react to changes such as mouse clicks or I/O events.

Traditional Spring MVC applications use annotations such as @GetMapping to map request paths to controller actions. Functional routing API is an alternative way of this mapping.

RouterFunction

RouterFunction represents a function that routes to a handler function.

Spring Boot RouterFunction example

In the following application we create a reactive Spring Boot application with functional routes.

build.gradle
...
src
├───main
│ ├───java
│ │ └───com
│ │ └───zetcode
│ │ │ Application.java
│ │ └───routes
│ │ MyRoutes.java
│ └───resources
└───test
 └───java
 └───com
 └───zetcode
 └───routes
 MyRoutesTest.java

This is the project structure of the Spring application.

plugins {
 id 'org.springframework.boot' version '3.1.1'
 id 'io.spring.dependency-management' version '1.1.0'
 id 'java'
}
group = 'com.zetcode'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'
repositories {
 mavenCentral()
}
dependencies {
 implementation 'org.springframework.boot:spring-boot-starter-webflux'
 testImplementation 'org.springframework.boot:spring-boot-starter-test'
}
test {
 useJUnitPlatform()
}

This is the build.gradle file. The RouterFunction is in the spring-boot-starter-webflux dependency.

package com.zetcode.routes;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.reactive.function.server.ServerResponse;
import static org.springframework.web.reactive.function.BodyInserters.fromValue;
import static org.springframework.web.reactive.function.server.RequestPredicates.GET;
import static org.springframework.web.reactive.function.server.RouterFunctions.route;
import static org.springframework.web.reactive.function.server.ServerResponse.ok;
@Configuration
public class MyRoutes {
 @Bean
 RouterFunction<ServerResponse> home() {
 return route(GET("/"), request -> ok().body(fromValue("Home page")));
 }
 @Bean
 RouterFunction<ServerResponse> about() {
 return route(GET("/about"), request -> ok().body(fromValue("About page")));
 }
}

We define two function routes.

@Bean
RouterFunction<ServerResponse> home() {
 return route(GET("/"), request -> ok().body(fromValue("Home page")));
}

With functional routes, we can write simple and elegant code. Here we return a simple text message for the home page.

package com.zetcode.routes;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.web.reactive.server.WebTestClient;
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class MyRoutesTest {
 @Autowired
 private WebTestClient client;
 @Test
 public void test_home_page() {
 client.get().uri("/").exchange().expectStatus().isOk()
 .expectBody(String.class).isEqualTo("Home page");
 }
 @Test
 public void test_about_page() {
 client.get().uri("/about").exchange().expectStatus().isOk()
 .expectBody(String.class).isEqualTo("About page");
 }
}

With WebTestClient, we test the two routes.

package com.zetcode;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class Application {
 public static void main(String[] args) {
 SpringApplication.run(Application.class, args);
 }
}

This code sets up the Spring Boot application.

$ ./gradlew bootRun

We run the application and navigate to localhost:8080.

In this article we have learned how to use functional routes with RouterFunction.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

List all Spring Boot tutorials.