Micronaut: property value placeholders usage in configuration files

Micronaut support the reuse of property values using place holders.

 

Example

appName: Chat Server
appVersion: 1.23.456
appDescription: ${appName} is used to send and receive messages from other users. Right now this app is at ${appVersion}

In the above example, appName, appVersion values are reused in appDescription.

 

Find the below working application.

 

Step 1: Create new maven project ‘micronaut-property-value-placeholder-demo’.

 

Step 2: Update pom.xml with maven dependencies.

 

pom.xml

<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>com.sample.app</groupId>
	<artifactId>micronaut-property-value-placeholder-demo</artifactId>
	<version>1</version>

	<properties>
		<maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
		<micronaut.version>3.7.3</micronaut.version>
		<slf4j.version>2.0.3</slf4j.version>
		<maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>

		<maven.compiler.target>15</maven.compiler.target>
		<maven.compiler.source>15</maven.compiler.source>
	</properties>

	<dependencies>

		<dependency>
			<groupId>io.micronaut</groupId>
			<artifactId>micronaut-inject-java</artifactId>
			<version>${micronaut.version}</version>
		</dependency>
		<dependency>
			<groupId>io.micronaut</groupId>
			<artifactId>micronaut-runtime</artifactId>
			<version>${micronaut.version}</version>
		</dependency>

		<dependency>
			<groupId>io.micronaut</groupId>
			<artifactId>micronaut-validation</artifactId>
			<version>${micronaut.version}</version>
		</dependency>


		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-api</artifactId>
			<version>${slf4j.version}</version>
		</dependency>
		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-simple</artifactId>
			<version>${slf4j.version}</version>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>${maven-compiler-plugin.version}</version>
				<configuration>
					<annotationProcessorPaths>
						<path>
							<groupId>io.micronaut</groupId>
							<artifactId>micronaut-validation</artifactId>
							<version>${micronaut.version}</version>
						</path>
					</annotationProcessorPaths>
				</configuration>
			</plugin>

			<plugin>
				<artifactId>maven-assembly-plugin</artifactId>
				<configuration>
					<archive>
						<manifest>
							<mainClass>com.sample.app.App</mainClass>
						</manifest>
					</archive>
					<descriptorRefs>
						<descriptorRef>jar-with-dependencies</descriptorRef>
					</descriptorRefs>
				</configuration>

				<executions>
					<execution>
						<id>make-assembly</id>
						<phase>package</phase>
						<goals>
							<goal>single</goal>
						</goals>
					</execution>
				</executions>
			</plugin>

		</plugins>
	</build>
</project>

Step 3: Create application.yml file under src/main/resources folder.

 

application.yml

appName: Chat Server
appVersion: 1.23.456
appDescription: ${appName} is used to send and receive messages from other users. Right now this app is at ${appVersion}

Step 4: Define main application class.

 

App.java

package com.sample.app;

import io.micronaut.context.ApplicationContext;
import io.micronaut.context.env.Environment;

public class App {

	public static void main(String[] args) {

		try (ApplicationContext applicationContext = ApplicationContext.run()) {
			
			Environment environment = applicationContext.getEnvironment();

			String appName = environment.getProperty("appName", String.class, "No appName found");
			String appVersion = environment.getProperty("appVersion", String.class, "No appVersion found");
			String appDescription = environment.getProperty("appDescription", String.class, "No description found");
			
			System.out.println("appName : " + appName);
			System.out.println("appVersion : " + appVersion);
			System.out.println("appDescription : " + appDescription);
			
		}

	}
}

Total project structure looks like below.

Build the project using mvn package command.

Navigate to the folder where pom.xml is located and execute the command ‘mvn package’.

 

Upon command successful execution, you can see the jar file ‘micronaut-property-value-placeholder-demo-1-jar-with-dependencies.jar’ in project target folder.

$ls ./target/
archive-tmp
classes
generated-sources
generated-test-sources
maven-archiver
maven-status
micronaut-property-value-placeholder-demo-1-jar-with-dependencies.jar
micronaut-property-value-placeholder-demo-1.jar
test-classes

Execute below command to run the application.

$java -jar ./target/micronaut-property-value-placeholder-demo-1-jar-with-dependencies.jar
appName : Chat Server
appVersion : 1.23.456
appDescription : Chat Server is used to send and receive messages from other users. Right now this app is at 1.23.456

You can download this application from this link.

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