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.

build.gradle

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.

com/zetcode/routes/MyRoutes.java

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.

com/zetcode/routes/MyRoutesTest.java

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.

com/zetcode/Application.java

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.

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