Quick Tour

Table of Contents

1. Dependencies
2. Application Code

We will take a quick tour of Spring for Apache Pulsar by showing a sample Spring Boot application that produces and consumes. This is a complete application and does not require any additional configuration, as long as you have a Pulsar cluster running on the default location - localhost:6650.

1. Dependencies

Spring Boot applications need only the spring-boot-starter-pulsar dependency. The following listings show how to define the dependency for Maven and Gradle, respectively:

Maven
Gradle

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-pulsar</artifactId>
        <version>3.4.0-SNAPSHOT</version>
    </dependency>
</dependencies>

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-pulsar:3.4.0-SNAPSHOT'
}

2. Application Code

The following listing shows the Spring Boot application case for the example:

@SpringBootApplication
public class PulsarBootHelloWorld {

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

    @Bean
    ApplicationRunner runner(PulsarTemplate<String> pulsarTemplate) {
        return (args) -> pulsarTemplate.send("hello-pulsar-topic", "Hello Pulsar World!");
    }

    @PulsarListener(subscriptionName = "hello-pulsar-sub", topics = "hello-pulsar-topic")
    void listen(String message) {
        System.out.println("Message Received: " + message);
    }
}

Let us quickly go through the higher-level details of this application. Later in the documentation we see these components in much more detail.

In the preceding sample, we heavily rely on Spring Boot auto-configuration. Spring Boot auto-configures several components for our application. It automatically provides a PulsarClient, which is used by both the producer and the consumer, for the application.

Spring Boot also auto-configures PulsarTemplate, which we inject in the application and start sending records to a Pulsar topic. The application sends messages to a topic named hello-pulsar. Note that the application does not specify any schema information, because Spring for Apache Pulsar library automatically infers the schema type from the type of the data that you send.

We use the PulsarListener annotation to consume from the hello-pulsar topic where we publish the data. PulsarListener is a convenience annotation that wraps the message listener container infrastructure in Spring for Apache Pulsar. Behind the scenes, it creates a message listener container to create and manage the Pulsar consumer. As with a regular Pulsar consumer, the default subscription type when using PulsarListener is the Exclusive mode. As records are published in to the hello-pulsar topic, the Pulsarlistener consumes them and prints them on the console. The framework also infers the schema type used from the data type that the PulsarListner method uses as the payload — String, in this case.