Spring Cloud Stream — Demo1

In this example, will give an overview about Spring Cloud Stream, followed by one example on how simple it is to write Kafka Processor using Spring Cloud Stream.

We’re using functional programming way to create topic (do not try in prod) and all spring cloud stream auto-configuration features will work.

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>
   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>2.7.3</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.example</groupId>
   <artifactId>spring-cloud-stream-demo</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>spring-cloud-stream-demo</name>
   <description>Demo project for Spring Boot</description>

   <properties>
      <java.version>11</java.version>
      <spring-cloud.version>2021.0.3</spring-cloud.version>
   </properties>

   <dependencies>
      <dependency>
         <groupId>org.springframework.cloud</groupId>
         <artifactId>spring-cloud-stream</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.cloud</groupId>
         <artifactId>spring-cloud-stream-binder-kafka</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.kafka</groupId>
         <artifactId>spring-kafka</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>org.springframework.cloud</groupId>
         <artifactId>spring-cloud-stream</artifactId>
         <scope>test</scope>
         <classifier>test-binder</classifier>
         <type>test-jar</type>
      </dependency>
      <dependency>
         <groupId>org.springframework.kafka</groupId>
         <artifactId>spring-kafka-test</artifactId>
         <scope>test</scope>
      </dependency>
   </dependencies>

   <dependencyManagement>
      <dependencies>
         <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>${spring-cloud.version}</version>
            <type>pom</type>
            <scope>import</scope>
         </dependency>
      </dependencies>
   </dependencyManagement>

   <build>
      <plugins>
         <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <configuration>
               <excludes>
                  <exclude>
                     <groupId>org.projectlombok</groupId>
                     <artifactId>lombok</artifactId>
                  </exclude>
               </excludes>
            </configuration>
         </plugin>
      </plugins>
   </build>

</project>

MainApp.java

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

import java.util.function.Function;

@SpringBootApplication
public class SpringCloudStreamProcessDemoApplication {

   public static void main(String[] args) {
      SpringApplication.run(SpringCloudStreamProcessDemoApplication.class, args);
   }

   // uppercase-in-0
   // uppercase-out-0
   @Bean
   public Function<String, String> toUppercase(){
      //return s -> s.toUpperCase();
      return String::toUpperCase;
   }
}

kafka-console-producer --bootstrap-server localhost:9092 --topic toUppercase-in-0
>hello spring
>hello
>java 9
      
kafka-console-consumer --bootstrap-server localhost:9092 --topic toUppercase-out-0
HELLO SPRING
HELLO
JAVA 9