001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements. See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache license, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License. You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the license for the specific language governing permissions and
015     * limitations under the license.
016     */
017    package org.apache.logging.log4j.core.appender;
018    
019    import java.util.ArrayList;
020    import java.util.List;
021    import java.util.Map;
022    
023    import org.apache.logging.log4j.LoggingException;
024    import org.apache.logging.log4j.core.Appender;
025    import org.apache.logging.log4j.core.Filter;
026    import org.apache.logging.log4j.core.LogEvent;
027    import org.apache.logging.log4j.core.config.AppenderControl;
028    import org.apache.logging.log4j.core.config.Configuration;
029    import org.apache.logging.log4j.core.config.plugins.Plugin;
030    import org.apache.logging.log4j.core.config.plugins.PluginAliases;
031    import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
032    import org.apache.logging.log4j.core.config.plugins.PluginConfiguration;
033    import org.apache.logging.log4j.core.config.plugins.PluginElement;
034    import org.apache.logging.log4j.core.config.plugins.PluginFactory;
035    import org.apache.logging.log4j.core.util.Booleans;
036    import org.apache.logging.log4j.core.util.Constants;
037    
038    /**
039     * The FailoverAppender will capture exceptions in an Appender and then route the event
040     * to a different appender. Hopefully it is obvious that the Appenders must be configured
041     * to not suppress exceptions for the FailoverAppender to work.
042     */
043    @Plugin(name = "Failover", category = "Core", elementType = "appender", printObject = true)
044    public final class FailoverAppender extends AbstractAppender {
045    
046        private static final long serialVersionUID = 1L;
047    
048        private static final int DEFAULT_INTERVAL_SECONDS = 60;
049    
050        private final String primaryRef;
051    
052        private final String[] failovers;
053    
054        private final Configuration config;
055    
056        private AppenderControl primary;
057    
058        private final List<AppenderControl> failoverAppenders = new ArrayList<AppenderControl>();
059    
060        private final long intervalMillis;
061    
062        private volatile long nextCheckMillis = 0;
063    
064        private FailoverAppender(final String name, final Filter filter, final String primary, final String[] failovers,
065                                 final int intervalMillis, final Configuration config, final boolean ignoreExceptions) {
066            super(name, filter, null, ignoreExceptions);
067            this.primaryRef = primary;
068            this.failovers = failovers;
069            this.config = config;
070            this.intervalMillis = intervalMillis;
071        }
072    
073    
074        @Override
075        public void start() {
076            final Map<String, Appender> map = config.getAppenders();
077            int errors = 0;
078            if (map.containsKey(primaryRef)) {
079                primary = new AppenderControl(map.get(primaryRef), null, null);
080            } else {
081                LOGGER.error("Unable to locate primary Appender " + primaryRef);
082                ++errors;
083            }
084            for (final String name : failovers) {
085                if (map.containsKey(name)) {
086                    failoverAppenders.add(new AppenderControl(map.get(name), null, null));
087                } else {
088                    LOGGER.error("Failover appender " + name + " is not configured");
089                }
090            }
091            if (failoverAppenders.isEmpty()) {
092                LOGGER.error("No failover appenders are available");
093                ++errors;
094            }
095            if (errors == 0) {
096                super.start();
097            }
098        }
099    
100        /**
101         * Handle the Log event.
102         * @param event The LogEvent.
103         */
104        @Override
105        public void append(final LogEvent event) {
106            if (!isStarted()) {
107                error("FailoverAppender " + getName() + " did not start successfully");
108                return;
109            }
110            final long localCheckMillis = nextCheckMillis;
111            if (localCheckMillis == 0 || System.currentTimeMillis() > localCheckMillis) {
112                callAppender(event);
113            } else {
114                failover(event, null);
115            }
116        }
117    
118        private void callAppender(final LogEvent event) {
119            try {
120                primary.callAppender(event);
121                nextCheckMillis = 0;
122            } catch (final Exception ex) {
123                nextCheckMillis = System.currentTimeMillis() + intervalMillis;
124                failover(event, ex);
125            }
126        }
127    
128        private void failover(final LogEvent event, final Exception ex) {
129            final RuntimeException re = ex != null ?
130                    (ex instanceof LoggingException ? (LoggingException)ex : new LoggingException(ex)) : null;
131            boolean written = false;
132            Exception failoverException = null;
133            for (final AppenderControl control : failoverAppenders) {
134                try {
135                    control.callAppender(event);
136                    written = true;
137                    break;
138                } catch (final Exception fex) {
139                    if (failoverException == null) {
140                        failoverException = fex;
141                    }
142                }
143            }
144            if (!written && !ignoreExceptions()) {
145                if (re != null) {
146                    throw re;
147                }
148                throw new LoggingException("Unable to write to failover appenders", failoverException);
149            }
150        }
151    
152        @Override
153        public String toString() {
154            final StringBuilder sb = new StringBuilder(getName());
155            sb.append(" primary=").append(primary).append(", failover={");
156            boolean first = true;
157            for (final String str : failovers) {
158                if (!first) {
159                    sb.append(", ");
160                }
161                sb.append(str);
162                first = false;
163            }
164            sb.append('}');
165            return sb.toString();
166        }
167    
168        /**
169         * Create a Failover Appender.
170         * @param name The name of the Appender (required).
171         * @param primary The name of the primary Appender (required).
172         * @param failovers The name of one or more Appenders to fail over to (at least one is required).
173         * @param retryIntervalSeconds The retry interval in seconds.
174         * @param config The current Configuration (passed by the Configuration when the appender is created).
175         * @param filter A Filter (optional).
176         * @param ignore If {@code "true"} (default) exceptions encountered when appending events are logged; otherwise
177         *               they are propagated to the caller.
178         * @return The FailoverAppender that was created.
179         */
180        @PluginFactory
181        public static FailoverAppender createAppender(
182                @PluginAttribute("name") final String name,
183                @PluginAttribute("primary") final String primary,
184                @PluginElement("Failovers") final String[] failovers,
185                @PluginAliases("retryInterval") // deprecated
186                @PluginAttribute("retryIntervalSeconds") final String retryIntervalSeconds,
187                @PluginConfiguration final Configuration config,
188                @PluginElement("Filter") final Filter filter,
189                @PluginAttribute("ignoreExceptions") final String ignore) {
190            if (name == null) {
191                LOGGER.error("A name for the Appender must be specified");
192                return null;
193            }
194            if (primary == null) {
195                LOGGER.error("A primary Appender must be specified");
196                return null;
197            }
198            if (failovers == null || failovers.length == 0) {
199                LOGGER.error("At least one failover Appender must be specified");
200                return null;
201            }
202    
203            final int seconds = parseInt(retryIntervalSeconds, DEFAULT_INTERVAL_SECONDS);
204            int retryIntervalMillis;
205            if (seconds >= 0) {
206                retryIntervalMillis = seconds * Constants.MILLIS_IN_SECONDS;
207            } else {
208                LOGGER.warn("Interval " + retryIntervalSeconds + " is less than zero. Using default");
209                retryIntervalMillis = DEFAULT_INTERVAL_SECONDS * Constants.MILLIS_IN_SECONDS;
210            }
211    
212            final boolean ignoreExceptions = Booleans.parseBoolean(ignore, true);
213    
214            return new FailoverAppender(name, filter, primary, failovers, retryIntervalMillis, config, ignoreExceptions);
215        }
216    }