Want to print properties loaded during spring boot application startup

Question

Can Anyone explain me what is happening in the below code?

1. What is the use of MapPropertySource?
2. What other options instead of MapPropertySource source and applicationConfig?
3. Why are we filtering in foreach?

    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("******************************************************************************");
    }```