protected void doConfigure()

in log4j-core/src/main/java/org/apache/logging/log4j/core/config/AbstractConfiguration.java [662:768]
100 lines of code
25 McCabe index (conditional complexity)

    protected void doConfigure() {
        processConditionals(rootNode);
        preConfigure(rootNode);
        configurationScheduler.start();
        // Find the "Properties" node first
        boolean hasProperties = false;
        for (final Node node : rootNode.getChildren()) {
            if ("Properties".equalsIgnoreCase(node.getName())) {
                hasProperties = true;
                createConfiguration(node, null);
                if (node.getObject() != null) {
                    final StrLookup lookup = node.getObject();
                    runtimeStrSubstitutor.setVariableResolver(lookup);
                    configurationStrSubstitutor.setVariableResolver(lookup);
                }
                break;
            }
        }
        if (!hasProperties) {
            final Map<String, String> map = this.getComponent(CONTEXT_PROPERTIES);
            final StrLookup lookup = map == null ? null : new PropertiesLookup(map);
            final Interpolator interpolator = new Interpolator(lookup, pluginPackages);
            interpolator.setConfiguration(this);
            interpolator.setLoggerContext(loggerContext.get());
            runtimeStrSubstitutor.setVariableResolver(interpolator);
            configurationStrSubstitutor.setVariableResolver(interpolator);
        }

        boolean setLoggers = false;
        boolean setRoot = false;
        for (final Node child : rootNode.getChildren()) {
            if ("Properties".equalsIgnoreCase(child.getName())) {
                // We already used this node
                continue;
            }
            createConfiguration(child, null);
            if (child.getObject() == null) {
                continue;
            }
            if ("Scripts".equalsIgnoreCase(child.getName())) {
                for (final AbstractScript script : child.getObject(AbstractScript[].class)) {
                    if (script instanceof ScriptRef) {
                        LOGGER.error(
                                "Script reference to {} not added. Scripts definition cannot contain script references",
                                script.getName());
                    } else if (scriptManager != null) {
                        scriptManager.addScript(script);
                    }
                }
            } else if ("Appenders".equalsIgnoreCase(child.getName())) {
                appenders = child.getObject();
            } else if (child.isInstanceOf(Filter.class)) {
                addFilter(child.getObject(Filter.class));
            } else if (child.isInstanceOf(Loggers.class)) {
                final Loggers l = child.getObject();
                loggerConfigs = l.getMap();
                setLoggers = true;
                if (l.getRoot() != null) {
                    root = l.getRoot();
                    setRoot = true;
                }
            } else if (child.isInstanceOf(CustomLevels.class)) {
                customLevels = child.getObject(CustomLevels.class).getCustomLevels();
            } else if (child.isInstanceOf(CustomLevelConfig.class)) {
                final List<CustomLevelConfig> copy = new ArrayList<>(customLevels);
                copy.add(child.getObject(CustomLevelConfig.class));
                customLevels = copy;
            } else if (child.isInstanceOf(AsyncWaitStrategyFactoryConfig.class)) {
                final AsyncWaitStrategyFactoryConfig awsfc = child.getObject(AsyncWaitStrategyFactoryConfig.class);
                asyncWaitStrategyFactory = awsfc.createWaitStrategyFactory();
            } else {
                final List<String> expected = Arrays.asList(
                        "\"Appenders\"", "\"Loggers\"", "\"Properties\"", "\"Scripts\"", "\"CustomLevels\"");
                LOGGER.error(
                        "Unknown object \"{}\" of type {} is ignored: try nesting it inside one of: {}.",
                        child.getName(),
                        child.getObject().getClass().getName(),
                        expected);
            }
        }

        if (!setLoggers) {
            LOGGER.warn("No Loggers were configured, using default. Is the Loggers element missing?");
            setToDefault();
            return;
        } else if (!setRoot) {
            LOGGER.warn(
                    "No Root logger was configured, creating default ERROR-level Root logger with Console appender");
            setToDefault();
            // return; // LOG4J2-219: creating default root=ok, but don't exclude configured Loggers
        }

        for (final Map.Entry<String, LoggerConfig> entry : loggerConfigs.entrySet()) {
            final LoggerConfig loggerConfig = entry.getValue();
            for (final AppenderRef ref : loggerConfig.getAppenderRefs()) {
                final Appender app = appenders.get(ref.getRef());
                if (app != null) {
                    loggerConfig.addAppender(app, ref.getLevel(), ref.getFilter());
                } else {
                    LOGGER.error(
                            "Unable to locate appender \"{}\" for logger config \"{}\"", ref.getRef(), loggerConfig);
                }
            }
        }

        setParents();
    }