private void loadConfig()

in winegrower-core/src/main/java/org/apache/winegrower/service/DefaultConfigurationAdmin.java [202:269]
46 lines of code
10 McCabe index (conditional complexity)

        private void loadConfig(final String pid) {
            final String prefix = "winegrower.service." + pid + "."; // for "global" registries like system props

            // we first read the config from the classpath (lowest priority)
            try (final InputStream embedConfig = Thread.currentThread().getContextClassLoader()
                    .getResourceAsStream(pid + WINEGROWER_CONFIG_EXTENSION)) {
                if (embedConfig != null) {
                    defaultConfig.putAll(load(embedConfig));
                }
            } catch (final IOException e) {
                throw new IllegalArgumentException(e);
            }
            properties.putAll(defaultConfig);

            // then the default registry which is considered "in JVM" so less prioritized than external config
            configRegistry.entrySet().stream().filter(it -> it.getKey().startsWith(prefix))
                    .forEach(entry -> properties.put(entry.getKey().substring(prefix.length()), entry.getValue()));

            // then from an external file
            if (defaultExternalConfigLocation.isFile()) {
                try (final InputStream stream = new FileInputStream(defaultExternalConfigLocation)) {
                    this.properties.putAll(load(stream));
                } catch (final IOException e) {
                    throw new IllegalArgumentException(e);
                }
            }

            final Map<String, String> placeholders = new HashMap<>(Map.class.cast(properties));
            placeholders.putAll(Map.class.cast(System.getProperties()));
            placeholders.putAll(System.getenv());
            final Substitutor substitutor = new Substitutor(placeholders);

            // and finally from system properties and env variables
            // (env is for the machine so less precise than system props so set first)
            final String envPrefix = prefix.toUpperCase(ROOT).replace('.', '_');
            System.getenv().keySet().stream()
                    .filter(it -> it.length() > prefix.length() && envPrefix.equalsIgnoreCase(it.substring(0, envPrefix.length())))
                    .forEach(key -> {
                        final String k = key.substring(envPrefix.length());
                        // env keys loose the case so in case it is important, enable to force the key name
                        // ex: to set configuration{pid=a.b.c, key=fooBar, value=dummy} you would set:
                        //     A_B_C_FOOBAR_NAME=fooBar
                        //     A_B_C_FOOBAR=dummy
                        // note that the FOOBAR in the key is not important, previous config is the same than:
                        //     A_B_C_1_NAME=fooBar
                        //     A_B_C_1=dummy
                        // but when there key is not ambiguous (all lowercase) it is simpler to set (key=foobar):
                        //     A_B_C_FOOBAR=dummy
                        final String value = System.getenv(key);
                        properties.put(
                                ofNullable(System.getenv(key + "_NAME")).orElseGet(() -> k.toLowerCase(ROOT)),
                                value.contains("${") && value.contains("}") ? substitutor.replace(value) : value);
                    });

            System.getProperties().stringPropertyNames().stream()
                    .filter(it -> it.startsWith(prefix))
                    .forEach(key -> {
                        final String value = System.getProperty(key);
                        properties.put(
                                key.substring(prefix.length()),
                                value.contains("${") && value.contains("}") ? substitutor.replace(value) : value);
                    });

            // ensure the factoryPid/pid is there if exists
            ofNullable(pid).ifPresent(v -> properties.putIfAbsent("service.pid", v));
            ofNullable(factoryPid).ifPresent(v -> properties.putIfAbsent("service.factoryPid", v));
            ofNullable(name).ifPresent(v -> properties.putIfAbsent("name", v));
        }