Let me explain it with below sample configuration.

app:   
  datasource:
    devSource:
      connection-timeout: 3000
      max-lifetime: 4000
      maximum-pool-size: 5
    qaSource:
      connection-timeout: 5000
      max-lifetime: 6000
      maximum-pool-size: 6
    prodSource:
      connection-timeout: 7000
      max-lifetime: 8000
      maximum-pool-size: 7

@EachProperty("app.datasource")
public class DataSourceConfiguration {

  private Integer connectionTimeout;

  private Integer maxLifetime;

  private Integer maximumPoolSize;

}

 

In the above example a new DataSourceConfiguration bean will be created for each item under the "app.datasource" key in application configuration.

A reference to the configuration entry name can be obtained with the @arameter annotation applied to a constructor argument.

public DataSourceConfiguration(@Parameter String name) {
    this.name = name;
}

 

In the above example for a configuration property of app.datasource. prodSource, the value of the name argument will be " prodSource".

 

How to get the beans?

The bean is created as a singleton with a Named qualifier matching the configuration entry name.

 

Example

DataSourceConfiguration devSource = applicationContext.getBean(DataSourceConfiguration.class,Qualifiers.byName("dev-source"));
DataSourceConfiguration qaSource = applicationContext.getBean(DataSourceConfiguration.class,Qualifiers.byName("qa-source"));
DataSourceConfiguration prodSource = applicationContext.getBean(DataSourceConfiguration.class,Qualifiers.byName("prod-source"));

 

Find the below working application.

 

Step 1: Create new maven project ‘micronaut-each-bean-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>4.0.0modelVersion>
  groupId>com.sample.appgroupId>
  artifactId>micronaut-each-bean-demoartifactId>
  version>1version>

  parent>
    groupId>io.micronautgroupId>
    artifactId>micronaut-parentartifactId>
    version>3.7.3version>
  parent>


  properties>
    maven-compiler-plugin.version>3.8.1maven-compiler-plugin.version>

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

  dependencies>

    dependency>
      groupId>io.micronautgroupId>
      artifactId>micronaut-inject-javaartifactId>
    dependency>

    dependency>
      groupId>org.slf4jgroupId>
      artifactId>slf4j-apiartifactId>
    dependency>
    dependency>
      groupId>org.slf4jgroupId>
      artifactId>slf4j-simpleartifactId>
    dependency>

  dependencies>

  build>
    plugins>
      plugin>
        groupId>org.apache.maven.pluginsgroupId>
        artifactId>maven-compiler-pluginartifactId>
        version>${maven-compiler-plugin.version}version>
        configuration>
          annotationProcessorPaths>
            path>
              groupId>io.micronautgroupId>
              artifactId>micronaut-inject-javaartifactId>
            path>
          annotationProcessorPaths>
        configuration>
      plugin>

      plugin>
        artifactId>maven-assembly-pluginartifactId>
        configuration>
          archive>
            manifest>
              mainClass>com.sample.app.AppmainClass>
            manifest>
          archive>
          descriptorRefs>
            descriptorRef>jar-with-dependenciesdescriptorRef>
          descriptorRefs>
        configuration>

        executions>
          execution>
            id>make-assemblyid>
            phase>packagephase>
            goals>
              goal>singlegoal>
            goals>
          execution>
        executions>
      plugin>


    plugins>
  build>
project>

 

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

 

application.yml

app:   
  datasource:
    devSource:
      connection-timeout: 3000
      max-lifetime: 4000
      maximum-pool-size: 5
    qaSource:
      connection-timeout: 5000
      max-lifetime: 6000
      maximum-pool-size: 6
    prodSource:
      connection-timeout: 7000
      max-lifetime: 8000
      maximum-pool-size: 7

 

Step 4: Define DataSourceConfiguration class.

 

DataSourceConfiguration.java

package com.sample.app.configuration;

import io.micronaut.context.annotation.EachProperty;
import io.micronaut.context.annotation.Parameter;

@EachProperty("app.datasource")
public class DataSourceConfiguration {

  private Integer connectionTimeout;

  private Integer maxLifetime;

  private Integer maximumPoolSize;

  private String name;

  public DataSourceConfiguration(@Parameter String name) {
    this.name = name;
  }

  public Integer getConnectionTimeout() {
    return connectionTimeout;
  }

  public void setConnectionTimeout(Integer connectionTimeout) {
    this.connectionTimeout = connectionTimeout;
  }

  public Integer getMaxLifetime() {
    return maxLifetime;
  }

  public void setMaxLifetime(Integer maxLifetime) {
    this.maxLifetime = maxLifetime;
  }

  public Integer getMaximumPoolSize() {
    return maximumPoolSize;
  }

  public void setMaximumPoolSize(Integer maximumPoolSize) {
    this.maximumPoolSize = maximumPoolSize;
  }

  @Override
  public String toString() {
    return "DataSourceConfiguration [connectionTimeout=" + connectionTimeout + ", maxLifetime=" + maxLifetime
        + ", maximumPoolSize=" + maximumPoolSize + ", name=" + name + "]";
  }

}

 

Step 5: Define main application class.

 

App.java

 

package com.sample.app;

import java.util.Collection;

import com.sample.app.configuration.DataSourceConfiguration;

import io.micronaut.context.ApplicationContext;
import io.micronaut.inject.qualifiers.Qualifiers;

public class App {

  public static void main(String[] args) {

    try (ApplicationContext applicationContext = ApplicationContext.run()) {

      DataSourceConfiguration devSource = applicationContext.getBean(DataSourceConfiguration.class,
          Qualifiers.byName("dev-source"));
      DataSourceConfiguration qaSource = applicationContext.getBean(DataSourceConfiguration.class,
          Qualifiers.byName("qa-source"));
      DataSourceConfiguration prodSource = applicationContext.getBean(DataSourceConfiguration.class,
          Qualifiers.byName("prod-source"));

      System.out.println(devSource);
      System.out.println(qaSource);
      System.out.println(prodSource +"\n");

      // Get all beans of given type
      Collection configs = applicationContext
          .getBeansOfType(DataSourceConfiguration.class);

      for (DataSourceConfiguration config : configs) {
        System.out.println(config);
      }
    }

  }
}

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-each-bean-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-each-bean-demo-1-jar-with-dependencies.jar
micronaut-each-bean-demo-1.jar
test-classes

Execute below command to run the application.

$java -jar ./target/micronaut-each-bean-demo-1-jar-with-dependencies.jar
DataSourceConfiguration [connectionTimeout=3000, maxLifetime=4000, maximumPoolSize=5, name=dev-source]
DataSourceConfiguration [connectionTimeout=5000, maxLifetime=6000, maximumPoolSize=6, name=qa-source]
DataSourceConfiguration [connectionTimeout=7000, maxLifetime=8000, maximumPoolSize=7, name=prod-source]

DataSourceConfiguration [connectionTimeout=7000, maxLifetime=8000, maximumPoolSize=7, name=prod-source]
DataSourceConfiguration [connectionTimeout=3000, maxLifetime=4000, maximumPoolSize=5, name=dev-source]
DataSourceConfiguration [connectionTimeout=5000, maxLifetime=6000, maximumPoolSize=6, name=qa-source]

You can download this application from this link.

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