core/src/main/java/org/apache/logging/log4j/core/appender/routing/RoutingAppender.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache license, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the license for the specific language governing permissions and
 * limitations under the license.
 */
package org.apache.logging.log4j.core.appender.routing;

import org.apache.logging.log4j.core.Appender;
import org.apache.logging.log4j.core.Filter;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.appender.AbstractAppender;
import org.apache.logging.log4j.core.appender.rewrite.RewritePolicy;
import org.apache.logging.log4j.core.config.AppenderControl;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.Node;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.config.plugins.PluginAttr;
import org.apache.logging.log4j.core.config.plugins.PluginConfiguration;
import org.apache.logging.log4j.core.config.plugins.PluginElement;
import org.apache.logging.log4j.core.config.plugins.PluginFactory;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * This Appender "routes" between various Appenders, some of which can be references to
 * Appenders defined earlier in the configuration while others can be dynamically created
 * within this Appender as required. Routing is achieved by specifying a pattern on
 * the Routing appender declaration. The pattern should contain one or more substitution patterns of
 * the form "$${[key:]token}". The pattern will be resolved each time the Appender is called using
 * the built in StrSubstitutor and the StrLookup plugin that matches the specified key.
 */
@Plugin(name = "Routing", type = "Core", elementType = "appender", printObject = true)
public final class RoutingAppender extends AbstractAppender {
    private static final String DEFAULT_KEY = "ROUTING_APPENDER_DEFAULT";
    private final Routes routes;
    private final Route defaultRoute;
    private final Configuration config;
    private final ConcurrentMap<String, AppenderControl> appenders = new ConcurrentHashMap<String, AppenderControl>();
    private final RewritePolicy rewritePolicy;

    private RoutingAppender(final String name, final Filter filter, final boolean handleException, final Routes routes,
                            final RewritePolicy rewritePolicy, final Configuration config) {
        super(name, filter, null, handleException);
        this.routes = routes;
        this.config = config;
        this.rewritePolicy = rewritePolicy;
        Route defRoute = null;
        for (final Route route : routes.getRoutes()) {
            if (route.getKey() == null) {
                if (defRoute == null) {
                    defRoute = route;
                } else {
                    error("Multiple default routes. Route " + route.toString() + " will be ignored");
                }
            }
        }
        defaultRoute = defRoute;
    }

    @Override
    public void start() {
        final Map<String, Appender<?>> map = config.getAppenders();
        // Register all the static routes.
        for (final Route route : routes.getRoutes()) {
            if (route.getAppenderRef() != null) {
                final Appender appender = map.get(route.getAppenderRef());
                if (appender != null) {
                    final String key = route == defaultRoute ? DEFAULT_KEY : route.getKey();
                    appenders.put(key, new AppenderControl(appender, null, null));
                } else {
                    LOGGER.error("Appender " + route.getAppenderRef() + " cannot be located. Route ignored");
                }
            }
        }
        super.start();
    }

    @Override
    public void stop() {
        super.stop();
        final Map<String, Appender<?>> map = config.getAppenders();
        for (final Map.Entry<String, AppenderControl> entry : appenders.entrySet()) {
            final String name = entry.getValue().getAppender().getName();
            if (!map.containsKey(name)) {
                entry.getValue().getAppender().stop();
            }
        }
    }

    public void append(LogEvent event) {
        if (rewritePolicy != null) {
            event = rewritePolicy.rewrite(event);
        }
        final String key = config.getSubst().replace(event, routes.getPattern());
        final AppenderControl control = getControl(key, event);
        if (control != null) {
            control.callAppender(event);
        }
    }

    private synchronized AppenderControl getControl(final String key, final LogEvent event) {
        AppenderControl control = appenders.get(key);
        if (control != null) {
            return control;
        }
        Route route = null;
        for (final Route r : routes.getRoutes()) {
            if (r.getAppenderRef() == null && key.equals(r.getKey())) {
                route = r;
                break;
            }
        }
        if (route == null) {
            route = defaultRoute;
        }
        if (route != null) {
            final Appender app = createAppender(route, event);
            if (app == null) {
                return null;
            }
            control = new AppenderControl(app, null, null);
            appenders.put(key, control);
        }

        return control;
    }

    private Appender createAppender(final Route route, final LogEvent event) {
        final Node routeNode = route.getNode();
        for (final Node node : routeNode.getChildren()) {
            if (node.getType().getElementName().equals("appender")) {
                final Node appNode = new Node(node);
                config.createConfiguration(appNode, event);
                if (appNode.getObject() instanceof Appender) {
                    final Appender app = (Appender) appNode.getObject();
                    app.start();
                    return app;
                }
                LOGGER.error("Unable to create Appender of type " + node.getName());
                return null;
            }
        }
        LOGGER.error("No Appender was configured for route " + route.getKey());
        return null;
    }

    /**
     * Create a RoutingAppender.
     * @param name The name of the Appender.
     * @param suppress "true" if exceptions should be hidden from the application, "false" otherwise.
     * The default is "true".
     * @param routes The routing definitions.
     * @param config The Configuration (automatically added by the Configuration).
     * @param rewritePolicy A RewritePolicy, if any.
     * @param filter A Filter to restrict events processed by the Appender or null.
     * @return The RoutingAppender
     */
    @PluginFactory
    public static RoutingAppender createAppender(@PluginAttr("name") final String name,
                                          @PluginAttr("suppressExceptions") final String suppress,
                                          @PluginElement("routes") final Routes routes,
                                          @PluginConfiguration final Configuration config,
                                          @PluginElement("rewritePolicy") final RewritePolicy rewritePolicy,
                                          @PluginElement("filters") final Filter filter) {

        final boolean handleExceptions = suppress == null ? true : Boolean.valueOf(suppress);

        if (name == null) {
            LOGGER.error("No name provided for RoutingAppender");
            return null;
        }
        if (routes == null) {
            LOGGER.error("No routes defined for RoutingAppender");
            return null;
        }
        return new RoutingAppender(name, filter, handleExceptions, routes, rewritePolicy, config);
    }
}