This guide walks you through the process of creating a functional reactive application that uses Spring Data to interact with Redis using the non-blocking Lettuce driver.

What you’ll build

You’ll build a Spring application that uses Spring Data Redis and Project Reactor to interact with a Redis data store reactively, storing and retrieving Coffee objects without blocking. This application uses Reactor’s Publisher implementations based upon the Reactive Streams specification, namely Mono (for a Publisher returning 0 or 1 value) and Flux (for a Publisher returning 0 to n values).

What you’ll need

How to complete this guide

Like most Spring Getting Started guides, you can start from scratch and complete each step or you can bypass basic setup steps that are already familiar to you. Either way, you end up with working code.

To start from scratch, move on to Build with Gradle.

To skip the basics, do the following:

When you finish, you can check your results against the code in gs-spring-data-reactive-redis/complete.

Build with Gradle

Build with Gradle

First you set up a basic build script. You can use any build system you like when building apps with Spring, but the code you need to work with Gradle and Maven is included here. If you’re not familiar with either, refer to Building Java Projects with Gradle or Building Java Projects with Maven.

Create the directory structure

In a project directory of your choosing, create the following subdirectory structure; for example, with mkdir -p src/main/java/hello on *nix systems:

└── src
    └── main
        └── java
            └── hello

Create a Gradle build file

Below is the initial Gradle build file.

build.gradle

buildscript {
	ext {
		springBootVersion = '2.2.1.RELEASE'
	}
	repositories {
		mavenCentral()
	}
	dependencies {
		classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
	}
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

bootJar {
    baseName = 'gs-spring-data-reactive-redis'
    version =  '0.1.0'
}

sourceCompatibility = 1.8
targetCompatibility = 1.8

repositories {
	mavenCentral()
}


dependencies {
	compile('org.springframework.boot:spring-boot-starter-data-redis-reactive')
	compile('org.springframework.boot:spring-boot-starter-webflux')
	compileOnly('org.projectlombok:lombok')
	testCompile('org.springframework.boot:spring-boot-starter-test')
	testCompile('io.projectreactor:reactor-test')
}

The Spring Boot gradle plugin provides many convenient features:

  • It collects all the jars on the classpath and builds a single, runnable "über-jar", which makes it more convenient to execute and transport your service.

  • It searches for the public static void main() method to flag as a runnable class.

  • It provides a built-in dependency resolver that sets the version number to match Spring Boot dependencies. You can override any version you wish, but it will default to Boot’s chosen set of versions.

Build with Maven

Build with Maven

First you set up a basic build script. You can use any build system you like when building apps with Spring, but the code you need to work with Maven is included here. If you’re not familiar with Maven, refer to Building Java Projects with Maven.

Create the directory structure

In a project directory of your choosing, create the following subdirectory structure; for example, with mkdir -p src/main/java/hello on *nix systems:

└── src
    └── main
        └── java
            └── hello

pom.xml

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.springframework</groupId>
    <artifactId>reactive-redis</artifactId>
    <version>0.1.0</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.1.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-data-redis-reactive</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-webflux</artifactId>
		</dependency>

		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
			<optional>true</optional>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>io.projectreactor</groupId>
			<artifactId>reactor-test</artifactId>
			<scope>test</scope>
		</dependency>
    </dependencies>

    <properties>
        <java.version>1.8</java.version>
    </properties>

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

</project>

The Spring Boot Maven plugin provides many convenient features:

  • It collects all the jars on the classpath and builds a single, runnable "über-jar", which makes it more convenient to execute and transport your service.

  • It searches for the public static void main() method to flag as a runnable class.

  • It provides a built-in dependency resolver that sets the version number to match Spring Boot dependencies. You can override any version you wish, but it will default to Boot’s chosen set of versions.

Build with your IDE

Build with your IDE

Create a domain class

Create a class representing a type of coffee we wish to stock in our coffee catalog.

src/main/java/hello/Coffee.java

package hello;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Coffee {
  private String id;
  private String name;
}
I use Lombok in this example to eliminate the boilerplate code for constructors and so-called "data class" methods ( accessors/mutators, equals(), toString(), & hashCode()).

Create a configuration class with Spring Beans supporting reactive Redis operations

src/main/java/hello/CoffeeConfiguration.java

package hello;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.redis.connection.ReactiveRedisConnectionFactory;
import org.springframework.data.redis.core.ReactiveRedisOperations;
import org.springframework.data.redis.core.ReactiveRedisTemplate;
import org.springframework.data.redis.serializer.Jackson2JsonRedisSerializer;
import org.springframework.data.redis.serializer.RedisSerializationContext;
import org.springframework.data.redis.serializer.StringRedisSerializer;

@Configuration
public class CoffeeConfiguration {
  @Bean
  ReactiveRedisOperations<String, Coffee> redisOperations(ReactiveRedisConnectionFactory factory) {
    Jackson2JsonRedisSerializer<Coffee> serializer = new Jackson2JsonRedisSerializer<>(Coffee.class);

    RedisSerializationContext.RedisSerializationContextBuilder<String, Coffee> builder =
        RedisSerializationContext.newSerializationContext(new StringRedisSerializer());

    RedisSerializationContext<String, Coffee> context = builder.value(serializer).build();

    return new ReactiveRedisTemplate<>(factory, context);
  }

}

Create a Spring Bean to load some sample data to our application when we start it

Since we may (re)start our application multiple times, we should first remove any data that may still exist from previous executions. We do this with a flushAll() (Redis) server command. Once we’ve flushed any existing data, we create a small Flux, map each coffee name to a Coffee object, and save it to the reactive Redis repository. We then query the repo for all values and display them.

src/main/java/hello/CoffeeLoader.java

package hello;

import org.springframework.data.redis.connection.ReactiveRedisConnectionFactory;
import org.springframework.data.redis.core.ReactiveRedisOperations;
import org.springframework.stereotype.Component;
import reactor.core.publisher.Flux;

import javax.annotation.PostConstruct;
import java.util.UUID;

@Component
public class CoffeeLoader {
  private final ReactiveRedisConnectionFactory factory;
  private final ReactiveRedisOperations<String, Coffee> coffeeOps;

  public CoffeeLoader(ReactiveRedisConnectionFactory factory, ReactiveRedisOperations<String, Coffee> coffeeOps) {
    this.factory = factory;
    this.coffeeOps = coffeeOps;
  }

  @PostConstruct
  public void loadData() {
    factory.getReactiveConnection().serverCommands().flushAll().thenMany(
        Flux.just("Jet Black Redis", "Darth Redis", "Black Alert Redis")
            .map(name -> new Coffee(UUID.randomUUID().toString(), name))
            .flatMap(coffee -> coffeeOps.opsForValue().set(coffee.getId(), coffee)))
        .thenMany(coffeeOps.keys("*")
            .flatMap(coffeeOps.opsForValue()::get))
        .subscribe(System.out::println);
  }
}

Create a RestController to provide an external interface for our application

src/main/java/hello/CoffeeController.java

package hello;

import org.springframework.data.redis.core.ReactiveRedisOperations;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import reactor.core.publisher.Flux;

@RestController
public class CoffeeController {
  private final ReactiveRedisOperations<String, Coffee> coffeeOps;

  CoffeeController(ReactiveRedisOperations<String, Coffee> coffeeOps) {
    this.coffeeOps = coffeeOps;
  }

  @GetMapping("/coffees")
  public Flux<Coffee> all() {
    return coffeeOps.keys("*")
        .flatMap(coffeeOps.opsForValue()::get);
  }
}

Make the application executable

Although it is possible to package this service as a traditional WAR file for deployment to an external application server, the simpler approach demonstrated below creates a standalone application. You package everything in a single, executable JAR file, driven by a good old Java main() method. Along the way, you use Spring’s support for embedding the Netty asynchronous "container" as the HTTP runtime instead of deploying to an external instance.

src/main/java/hello/Application.java

package hello;

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);
  }
}

@SpringBootApplication is a convenience annotation that adds all of the following:

  • @Configuration: Tags the class as a source of bean definitions for the application context.

  • @EnableAutoConfiguration: Tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings. For example, if spring-webmvc is on the classpath, this annotation flags the application as a web application and activates key behaviors, such as setting up a DispatcherServlet.

  • @ComponentScan: Tells Spring to look for other components, configurations, and services in the hello package, letting it find the controllers.

The main() method uses Spring Boot’s SpringApplication.run() method to launch an application. Did you notice that there was not a single line of XML? There is no web.xml file, either. This web application is 100% pure Java and you did not have to deal with configuring any plumbing or infrastructure.

Build an executable JAR

You can run the application from the command line with Gradle or Maven. You can also build a single executable JAR file that contains all the necessary dependencies, classes, and resources and run that. Building an executable jar makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.

If you use Gradle, you can run the application by using ./gradlew bootRun. Alternatively, you can build the JAR file by using ./gradlew build and then run the JAR file, as follows:

java -jar build/libs/gs-spring-data-reactive-redis-0.1.0.jar

If you use Maven, you can run the application by using ./mvnw spring-boot:run. Alternatively, you can build the JAR file with ./mvnw clean package and then run the JAR file, as follows:

java -jar target/gs-spring-data-reactive-redis-0.1.0.jar
The steps described here create a runnable JAR. You can also build a classic WAR file.

Test the application

Now that the application is running, you can test it by accessing http://localhost:8080/coffees from HTTPie, curl, or your favorite browser.

Summary

Congratulations! You’ve just developed a Spring application that uses Spring Data and Redis for fully reactive, non-blocking database access!

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