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.PluginAttribute;
031    import org.apache.logging.log4j.core.config.plugins.PluginConfiguration;
032    import org.apache.logging.log4j.core.config.plugins.PluginElement;
033    import org.apache.logging.log4j.core.config.plugins.PluginFactory;
034    import org.apache.logging.log4j.core.util.Booleans;
035    import org.apache.logging.log4j.core.util.Constants;
036    
037    /**
038     * The FailoverAppender will capture exceptions in an Appender and then route the event
039     * to a different appender. Hopefully it is obvious that the Appenders must be configured
040     * to not suppress exceptions for the FailoverAppender to work.
041     */
042    @Plugin(name = "Failover", category = "Core", elementType = "appender", printObject = true)
043    public final class FailoverAppender extends AbstractAppender {
044    
045        private static final int DEFAULT_INTERVAL_SECONDS = 60;
046    
047        private final String primaryRef;
048    
049        private final String[] failovers;
050    
051        private final Configuration config;
052    
053        private AppenderControl primary;
054    
055        private final List<AppenderControl> failoverAppenders = new ArrayList<AppenderControl>();
056    
057        private final long intervalMillis;
058    
059        private volatile long nextCheckMillis = 0;
060    
061        private FailoverAppender(final String name, final Filter filter, final String primary, final String[] failovers,
062                                 final int intervalMillis, final Configuration config, final boolean ignoreExceptions) {
063            super(name, filter, null, ignoreExceptions);
064            this.primaryRef = primary;
065            this.failovers = failovers;
066            this.config = config;
067            this.intervalMillis = intervalMillis;
068        }
069    
070    
071        @Override
072        public void start() {
073            final Map<String, Appender> map = config.getAppenders();
074            int errors = 0;
075            if (map.containsKey(primaryRef)) {
076                primary = new AppenderControl(map.get(primaryRef), null, null);
077            } else {
078                LOGGER.error("Unable to locate primary Appender " + primaryRef);
079                ++errors;
080            }
081            for (final String name : failovers) {
082                if (map.containsKey(name)) {
083                    failoverAppenders.add(new AppenderControl(map.get(name), null, null));
084                } else {
085                    LOGGER.error("Failover appender " + name + " is not configured");
086                }
087            }
088            if (failoverAppenders.isEmpty()) {
089                LOGGER.error("No failover appenders are available");
090                ++errors;
091            }
092            if (errors == 0) {
093                super.start();
094            }
095        }
096    
097        /**
098         * Handle the Log event.
099         * @param event The LogEvent.
100         */
101        @Override
102        public void append(final LogEvent event) {
103            if (!isStarted()) {
104                error("FailoverAppender " + getName() + " did not start successfully");
105                return;
106            }
107            final long localCheckMillis = nextCheckMillis;
108            if (localCheckMillis == 0 || System.currentTimeMillis() > localCheckMillis) {
109                callAppender(event);
110            } else {
111                failover(event, null);
112            }
113        }
114    
115        private void callAppender(final LogEvent event) {
116            try {
117                primary.callAppender(event);
118                nextCheckMillis = 0;
119            } catch (final Exception ex) {
120                nextCheckMillis = System.currentTimeMillis() + intervalMillis;
121                failover(event, ex);
122            }
123        }
124    
125        private void failover(final LogEvent event, final Exception ex) {
126            final RuntimeException re = ex != null ?
127                    (ex instanceof LoggingException ? (LoggingException)ex : new LoggingException(ex)) : null;
128            boolean written = false;
129            Exception failoverException = null;
130            for (final AppenderControl control : failoverAppenders) {
131                try {
132                    control.callAppender(event);
133                    written = true;
134                    break;
135                } catch (final Exception fex) {
136                    if (failoverException == null) {
137                        failoverException = fex;
138                    }
139                }
140            }
141            if (!written && !ignoreExceptions()) {
142                if (re != null) {
143                    throw re;
144                } else {
145                    throw new LoggingException("Unable to write to failover appenders", failoverException);
146                }
147            }
148        }
149    
150        @Override
151        public String toString() {
152            final StringBuilder sb = new StringBuilder(getName());
153            sb.append(" primary=").append(primary).append(", failover={");
154            boolean first = true;
155            for (final String str : failovers) {
156                if (!first) {
157                    sb.append(", ");
158                }
159                sb.append(str);
160                first = false;
161            }
162            sb.append('}');
163            return sb.toString();
164        }
165    
166        /**
167         * Create a Failover Appender.
168         * @param name The name of the Appender (required).
169         * @param primary The name of the primary Appender (required).
170         * @param failovers The name of one or more Appenders to fail over to (at least one is required).
171         * @param retryIntervalString The retry intervalMillis.
172         * @param config The current Configuration (passed by the Configuration when the appender is created).
173         * @param filter A Filter (optional).
174         * @param ignore If {@code "true"} (default) exceptions encountered when appending events are logged; otherwise
175         *               they are propagated to the caller.
176         * @return The FailoverAppender that was created.
177         */
178        @PluginFactory
179        public static FailoverAppender createAppender(
180                @PluginAttribute("name") final String name,
181                @PluginAttribute("primary") final String primary,
182                @PluginElement("Failovers") final String[] failovers,
183                @PluginAttribute("retryInterval") final String retryIntervalString,
184                @PluginConfiguration final Configuration config,
185                @PluginElement("Filter") final Filter filter,
186                @PluginAttribute("ignoreExceptions") final String ignore) {
187            if (name == null) {
188                LOGGER.error("A name for the Appender must be specified");
189                return null;
190            }
191            if (primary == null) {
192                LOGGER.error("A primary Appender must be specified");
193                return null;
194            }
195            if (failovers == null || failovers.length == 0) {
196                LOGGER.error("At least one failover Appender must be specified");
197                return null;
198            }
199    
200            final int seconds = parseInt(retryIntervalString, DEFAULT_INTERVAL_SECONDS);
201            int retryIntervalMillis;
202            if (seconds >= 0) {
203                retryIntervalMillis = seconds * Constants.MILLIS_IN_SECONDS;
204            } else {
205                LOGGER.warn("Interval " + retryIntervalString + " is less than zero. Using default");
206                retryIntervalMillis = DEFAULT_INTERVAL_SECONDS * Constants.MILLIS_IN_SECONDS;
207            }
208    
209            final boolean ignoreExceptions = Booleans.parseBoolean(ignore, true);
210    
211            return new FailoverAppender(name, filter, primary, failovers, retryIntervalMillis, config, ignoreExceptions);
212        }
213    }