Spring Boot AMQP - Connection Creation / Queue Declaration at Startup

Question

Spring boot 2.3.1 spring-boot-starter-amqp

If I run a spring boot app as a java application by running the main method (Intellij - Create a Run Configuration of type Application and provide the main class DemoApplication), RabbitMQ connection is not created at startup. However when I run as a Spring Boot app (Intellij - Create a Run Configuration of type Spring Boot and provide the main class DemoApplication) RabbitMQ connection is created during the startup.

What is the difference between the two? Why can't RabbitMQ create a connection on startup when the main method is run as java application? This line does not appear.

INFO 32385 --- [*.*.*.*] o.s.a.r.c.CachingConnectionFactory       : Created new connection: rabbitConnectionFactory.publisher#3f499c2f:0/SimpleConnection@4e5ef6a0 [delegate=amqp://guest@127.0.0.1:5672/, localPort= 62061]

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>2.3.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>14</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-amqp</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</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>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.amqp</groupId>
            <artifactId>spring-rabbit-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>

application.yaml

spring:
  rabbitmq:
    host: ${RABBITMQ_HOST:localhost}
    port: ${RABBITMQ_PORT:5672}
    username: ${RABBITMQ_USERNAME:guest}
    password: ${RABBITMQ_PASSWORD:guest}

Main class

package com.example.demo;

import org.springframework.amqp.core.Binding;
import org.springframework.amqp.core.BindingBuilder;
import org.springframework.amqp.core.DirectExchange;
import org.springframework.amqp.core.Queue;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class DemoApplication {

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

    @Bean
    DirectExchange demoExchange() {
        return new DirectExchange("demo-exchange");
    }

    @Bean
    Queue demoQueue() {
        return new Queue("demo-queue");
    }

    @Bean
    Binding demoBinding() {
        return BindingBuilder.bind(demoQueue()).to(demoExchange()).with("demo-routing");
    }

}

Intellij - Create a Run Configuration of type Application and provide the main class (DemoApplication)

Answer 1

You have nothing in your code that opens a connection (e.g. @RabbitListener).

Perhaps the actuator (RabbitHealthIndicator) is opening a connection - not sure why it would make a difference how you launch it though.

I don't see a connection running either way (with STS).

If you add a @RabbitListener to your app; you will see a connection either way.