Spring Boot RouterFunction tutorial

last modified July 6, 2020

Spring Boot RouterFunction tutorial shows 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.

pom.xml
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.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
         http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.zetcode</groupId>
    <artifactId>springbootrouterfunction</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <properties>
        <java.version>13</java.version>
    </properties>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.4.RELEASE</version>
    </parent>

    <dependencies>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

This is the Maven pom.xml 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.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.reactive.server.WebTestClient;

@RunWith(SpringRunner.class)
@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.

$ mvn spring-boot:run

We run the application and navigate to localhost:8080.

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

List all Spring Boot tutorials.