Great questions—Quarkus has flexible, production-ready tools for handling external and runtime configuration, so let’s break this down step by step.

1. Reading External/Runtime Properties Files (Including application.properties) #

Quarkus offers multiple practical ways to load configuration from outside your packaged app or adjust it at runtime:

• Specify external config file paths via system property
  When starting your app, use the quarkus.config.locations system property to point to external files. You can use absolute paths, relative paths, or classpath references. For example:

  java -jar your-app-runner.jar -Dquarkus.config.locations=file:/opt/config/external-application.properties,classpath:/another-config.properties
  

  Quarkus will load these files alongside the internal application.properties, with external values overriding internal ones automatically.

• Use environment variables
  Quarkus maps configuration properties to environment variables seamlessly (uppercase property names, dots replaced with underscores). For example, quarkus.mailer.to becomes QUARKUS_MAILER_TO. Set this variable at runtime (e.g., in Docker, Kubernetes, or your OS) and Quarkus will pick it up without modifying any files—perfect for containerized deployments.

• Dynamic configuration refresh
  If you need to update properties while the app is running, first enable refresh in your base config:

  quarkus.config.refresh.enabled=true
  

  After modifying your external properties file, send a POST request to the /q/config/refresh endpoint (enabled by default in dev mode; secure it for production). Any beans using @ConfigProperty will automatically pick up the new values without restarting the app.

2. Quarkus-Specific External Config for Mail Senders (Including Externalizing application.properties) #

Absolutely—Quarkus is built to make this straightforward, even for mail sender use cases:

• Fully externalize your application.properties
  You can move your entire application.properties file outside your app package and point to it using the quarkus.config.locations system property mentioned earlier. For example:

  java -jar your-mail-app-runner.jar -Dquarkus.config.locations=file:/opt/mail-config/application.properties
  

  Quarkus will load this external file as the primary config source, so all your mailer settings (recipients, SMTP server, credentials, etc.) can be managed externally without rebuilding the app.

• Quarkus-native way to inject external recipient lists
  Use MicroProfile Config's @ConfigProperty annotation to inject recipient values directly into your mail sender code, which pulls automatically from your external config. Here’s a practical example:

  import io.quarkus.mailer.Mail;
  import io.quarkus.mailer.Mailer;
  import jakarta.inject.Inject;
  import jakarta.ws.rs.POST;
  import jakarta.ws.rs.Path;
  import org.eclipse.microprofile.config.inject.ConfigProperty;
  import java.util.List;
  
  @Path("/send-email")
  public class MailSenderResource {
  
      @Inject
      Mailer mailer;
  
      // Inject recipients from external config (uses default if not set)
      @ConfigProperty(name = "app.mail.recipients", defaultValue = "admin@example.com")
      List<String> emailRecipients;
  
      @POST
      public void sendNotification() {
          mailer.send(Mail.withText(
              emailRecipients,
              "System Notification",
              "This is an automated message from your Quarkus app."
          ));
      }
  }
  

  In your external application.properties, just define the recipients as a comma-separated list:

  app.mail.recipients=user1@domain.com,user2@domain.com,team@domain.com
  

• Profile-specific external config
  For different environments (dev, staging, prod), create profile-specific external files like application-prod.properties and activate the profile at runtime:

  java -jar your-app-runner.jar -Dquarkus.profile=prod -Dquarkus.config.locations=file:/opt/config/
  

  Quarkus will automatically load the matching profile file from the specified directory, making environment-specific mail configuration simple.

内容的提问来源于stack exchange，提问作者fatherazrael