java - How to log the active configuration in a Spring Boot application?

Question

I would really like to use YAML config for Spring Boot, as I find it quite readable and useful to have a single file showing what properties are active in my different profiles. Unfortunately, I'm finding that setting properties in application.yml can be rather fragile.

Things like using a tab instead of spaces will cause properties to not exist (without warnings as far as I can see), and all too often I find that my active profiles are not being set, due to some unknown issue with my YAML.

So I was wondering whether there are any hooks that would enable me to get hold of the currently active profiles and properties, so that I could log them.

Similarly, is there a way to cause start-up to fail if the application.yml contains errors? Either that or a means for me to validate the YAML myself, so that I could kill the start-up process.

Answer 1

In addition to other answers: logging active properties on context refreshed event.

Java 8

package mypackage;

import lombok.extern.slf4j.Slf4j;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.context.event.EventListener;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.MapPropertySource;
import org.springframework.stereotype.Component;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

@Slf4j
@Component
public class AppContextEventListener {

    @EventListener
    public void handleContextRefreshed(ContextRefreshedEvent event) {
        printActiveProperties((ConfigurableEnvironment) event.getApplicationContext().getEnvironment());
    }

    private void printActiveProperties(ConfigurableEnvironment env) {

        System.out.println("************************* ACTIVE APP PROPERTIES ******************************");

        List<MapPropertySource> propertySources = new ArrayList<>();

        env.getPropertySources().forEach(it -> {
            if (it instanceof MapPropertySource && it.getName().contains("applicationConfig")) {
                propertySources.add((MapPropertySource) it);
            }
        });

        propertySources.stream()
                .map(propertySource -> propertySource.getSource().keySet())
                .flatMap(Collection::stream)
                .distinct()
                .sorted()
                .forEach(key -> {
                    try {
                        System.out.println(key + "=" + env.getProperty(key));
                    } catch (Exception e) {
                        log.warn("{} -> {}", key, e.getMessage());
                    }
                });
        System.out.println("******************************************************************************");
    }
}

Kotlin

package mypackage

import mu.KLogging
import org.springframework.context.event.ContextRefreshedEvent
import org.springframework.context.event.EventListener
import org.springframework.core.env.ConfigurableEnvironment
import org.springframework.core.env.MapPropertySource
import org.springframework.stereotype.Component

@Component
class AppContextEventListener {

    companion object : KLogging()

    @EventListener
    fun handleContextRefreshed(event: ContextRefreshedEvent) {
        printActiveProperties(event.applicationContext.environment as ConfigurableEnvironment)
    }

    fun printActiveProperties(env: ConfigurableEnvironment) {
        println("************************* ACTIVE APP PROPERTIES ******************************")
        env.propertySources
                .filter { it.name.contains("applicationConfig") }
                .map { it as EnumerablePropertySource<*> }
                .map { it -> it.propertyNames.toList() }
                .flatMap { it }
                .distinctBy { it }
                .sortedBy { it }
                .forEach { it ->
                    try {
                        println("$it=${env.getProperty(it)}")
                    } catch (e: Exception) {
                        logger.warn("$it -> ${e.message}")
                    }
                }
        println("******************************************************************************")
    }
}

Output like:

************************* ACTIVE APP PROPERTIES ******************************
server.port=3000
spring.application.name=my-app
...
2017-12-29 13:13:32.843  WARN 36252 --- [           main] m.AppContextEventListener        : spring.boot.admin.client.service-url -> Could not resolve placeholder 'management.address' in value "http://${management.address}:${server.port}"
...
spring.datasource.password=
spring.datasource.url=jdbc:postgresql://localhost/my_db?currentSchema=public
spring.datasource.username=db_user
...
******************************************************************************