java - Log4j2 RollingFile Appender - 在每个日志文件的开头添加自定义信息

Question

在 java 1.7 中使用 log4j2 (beta9)。

我完整的 log4j2.xml:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration>
  <Properties>
    <Property name="projectPrefix">Tts</Property>
    <Property name="rawPattern">%d %-5p [%t] %C{2} (%F:%L) - %m%n</Property>
    <Property name="coloredPattern">%d %highlight{%-5p}{FATAL=bright red, ERROR=red, WARN=yellow, INFO=cyan, DEBUG=green, TRACE=bright blue} %style{[%t] %C{2} (%F:%L) -}{bright,black} %m%n</Property>
    <Property name="fileName">Log/${projectPrefix}.log</Property>
    <Property name="filePattern">Log/${projectPrefix}-%i.log</Property>
  </Properties>
  <Appenders>
    <Console name="Stdout" target="SYSTEM_OUT">
      <PatternLayout pattern="${coloredPattern}"/>
    </Console>
    <RollingFile name="Logfile" fileName="${fileName}" filePattern="${filePattern}">
      <PatternLayout pattern="${rawPattern}"/>
      <Policies>
        <SizeBasedTriggeringPolicy size="16 MB"/>
      </Policies>
      <DefaultRolloverStrategy fileIndex="min" max="16"/>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="info">
      <AppenderRef ref="Stdout"/>
      <AppenderRef ref="Logfile"/>
    </Root>
  </Loggers>
</Configuration>

我想在每个日志文件的顶部添加一些自定义信息，例如我的应用程序的版本字符串、应用程序正常运行时间和系统正常运行时间。甚至在刚刚关闭的日志文件的底部写一些 »bye, bye/eof« 也可以。

当 RollingFileAppander 创建了一个新文件时，是否有类似钩子(Hook)或回调的东西来得到通知，以便我可以首先将我的东西放入这些新日志文件(或任何其他建议)？

Answer 1

好的，通过像 here 中描述的那样扩展 DefaultRolloverStrategy，可以解决这个问题。 .但是

• 它需要大约 150 行代码(包括包装 RolloverDescription 和 appender.rolling.helper.Action)和
• 有点味道，因为需要完全复制 DefaultRolloverStrategy 的工厂方法(使该解决方案维护不友好，例如，如果 DefaultRolloverStrategy 在未来版本中获得更多配置参数)

要让log4j2调用我们的工厂方法，log4j2.xml的根标签必须带有我们类的包属性，例如:

<Configuration packages="de.jme.toolbox.logging">
...
</Configuration>

在我们自己的 RolloverStrategy 中，我们必须处理 @Plugin 和 @PluginFactory，如 here 所述.

最后是我完整的 log4j2.xml(您不需要所有这些属性 - 这正是我喜欢的配置日志记录的方式):

<?xml version="1.0" encoding="UTF-8"?>
<Configuration packages="de.jme.toolbox.logging">
  <Properties>
    <Property name="projectPrefix">Tts</Property>
    <Property name="rawPattern">%d %-5p [%t] %C{2} (%F:%L) - %m%n</Property>
    <Property name="coloredPattern">%d %highlight{%-5p}{FATAL=bright red, ERROR=red, WARN=yellow, INFO=cyan, DEBUG=green, TRACE=bright blue} %style{[%t] %C{2} (%F:%L) -}{bright,black} %m%n</Property>
    <Property name="coloredShortPattern">%d %highlight{%-5p}{FATAL=bright red, ERROR=red, WARN=yellow, INFO=cyan, DEBUG=green, TRACE=bright blue} %style{[%t] -}{bright,black} %m%n</Property>
    <Property name="fileName">Log/${projectPrefix}.log</Property>
    <Property name="filePattern">Log/${projectPrefix}-%i.log</Property>
  </Properties>
  <Appenders>
    <Console name="Stdout" target="SYSTEM_OUT">
      <PatternLayout pattern="${coloredPattern}"/>
    </Console>
    <RollingFile name="Logfile" fileName="${fileName}" filePattern="${filePattern}">
      <PatternLayout pattern="${rawPattern}"/>
      <Policies>
        <SizeBasedTriggeringPolicy size="1 MB"/>
      </Policies>
      <MyRolloverStrategy fileIndex="min" max="16"/>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="info">
      <AppenderRef ref="Stdout"/>
      <AppenderRef ref="Logfile"/>
    </Root>
  </Loggers>
</Configuration>

这里是 MyRolloverStrategy.java:

package de.jme.toolbox.logging;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.zip.Deflater;

import org.apache.logging.log4j.core.appender.rolling.DefaultRolloverStrategy;
import org.apache.logging.log4j.core.appender.rolling.RollingFileManager;
import org.apache.logging.log4j.core.appender.rolling.RolloverDescription;
import org.apache.logging.log4j.core.appender.rolling.helper.Action;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
import org.apache.logging.log4j.core.config.plugins.PluginConfiguration;
import org.apache.logging.log4j.core.config.plugins.PluginFactory;
import org.apache.logging.log4j.core.helpers.Integers;
import org.apache.logging.log4j.core.lookup.StrSubstitutor;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.status.StatusLogger;

/**
 * Own RolloverStrategy to hook the DefaultRolloverStrategy's rollover events
 *
 * Siehe auch:
 * - https://issues.apache.org/jira/browse/LOG4J2-486
 * - http://apache-logging.6191.n7.nabble.com/log4j2-getting-started-amp-rolling-files-tt8406.html#a42402
 * - http://stackoverflow.com/questions/20819376/log4j2-rollingfile-appender-add-custom-info-at-the-start-of-each-logfile
 *
 * @author Joe Merten
 */
@org.apache.logging.log4j.core.config.plugins.Plugin(name="MyRolloverStrategy", category="Core", printObject=true)
public class MyRolloverStrategy extends DefaultRolloverStrategy {

    protected static final Logger logger = StatusLogger.getLogger();

    // ==============================
    // ↓↓↓ Some stuff copied from ↓↓↓
    // https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/rolling/DefaultRolloverStrategy.java r1556050
    // Just changed »DefaultRolloverStrategy« to »MyRolloverStrategy«

    private static final int MIN_WINDOW_SIZE = 1;
    private static final int DEFAULT_WINDOW_SIZE = 7;

    @PluginFactory
    public static MyRolloverStrategy createStrategy(
            @PluginAttribute("max") final String max,
            @PluginAttribute("min") final String min,
            @PluginAttribute("fileIndex") final String fileIndex,
            @PluginAttribute("compressionLevel") final String compressionLevelStr,
            @PluginConfiguration final Configuration config) {
        final boolean useMax = fileIndex == null ? true : fileIndex.equalsIgnoreCase("max");
        int minIndex;
        if (min != null) {
            minIndex = Integer.parseInt(min);
            if (minIndex < 1) {
                LOGGER.error("Minimum window size too small. Limited to " + MIN_WINDOW_SIZE);
                minIndex = MIN_WINDOW_SIZE;
            }
        } else {
            minIndex = MIN_WINDOW_SIZE;
        }
        int maxIndex;
        if (max != null) {
            maxIndex = Integer.parseInt(max);
            if (maxIndex < minIndex) {
                maxIndex = minIndex < DEFAULT_WINDOW_SIZE ? DEFAULT_WINDOW_SIZE : minIndex;
                LOGGER.error("Maximum window size must be greater than the minimum windows size. Set to " + maxIndex);
            }
        } else {
            maxIndex = DEFAULT_WINDOW_SIZE;
        }
        final int compressionLevel = Integers.parseInt(compressionLevelStr, Deflater.DEFAULT_COMPRESSION);
        return new MyRolloverStrategy(minIndex, maxIndex, useMax, compressionLevel, config.getStrSubstitutor());
    }
    // ↑↑↑ Some stuff copied from ↑↑↑
    // ==============================

    protected MyRolloverStrategy(int minIndex, int maxIndex, boolean useMax, int compressionLevel, StrSubstitutor subst) {
        super(minIndex, maxIndex, useMax, compressionLevel, subst);
    }

    // Wrapper class only for setting a hook to execute()
    static class MyAction implements Action {
        final Action delegate;
        final String fileName;

        public MyAction(final Action delegate, final String fileName) {
            this.delegate = delegate;
            this.fileName = fileName;
        }

        @Override public void run() {
            delegate.run();
        }

        @Override public boolean execute() throws IOException {
            try {
                BufferedWriter writer = null;
                try {
                    writer = new BufferedWriter(new FileWriter(new File(fileName), true));
                    writer.write("****************************\n");
                    writer.write("*** Bye, bye old logfile ***\n");
                    writer.write("****************************\n");
                } finally {
                    if (writer != null)
                        writer.close();
                }
            } catch (Throwable e) {
                logger.error("Writing to bottom of old logfile \"" + fileName + "\" with", e);
            }

            boolean ret = delegate.execute();

            try {
                BufferedWriter writer = null;
                try {
                    writer = new BufferedWriter(new FileWriter(new File(fileName), true));
                    writer.write("*************************\n");
                    writer.write("*** Hello new logfile ***\n");
                    writer.write("*************************\n");
                } finally {
                    if (writer != null)
                        writer.close();
                }
            } catch (Throwable e) {
                logger.error("Writing to top of new logfile \"" + fileName + "\" with", e);
            }

            return ret;
        }

        @Override public void close() {
            delegate.close();
        }

        @Override public boolean isComplete() {
            return delegate.isComplete();
        }
    }

    // Wrapper class only for setting a hook to getSynchronous().execute()
    static class MyRolloverDescription implements RolloverDescription {
        final RolloverDescription delegate;

        public MyRolloverDescription(final RolloverDescription delegate) {
            this.delegate = delegate;
        }

        @Override public String getActiveFileName() {
            return delegate.getActiveFileName();
        }

        @Override public boolean getAppend() {
            //return delegate.getAppend();
            // As long as we already put some data to the top of the new logfile, subsequent writes should be performed with "append".
            return true;
        }

        // The synchronous action is for renaming, here we want to hook
        @Override public Action getSynchronous() {
            Action delegateAction = delegate.getSynchronous();
            if (delegateAction == null) return null;
            return new MyAction(delegateAction, delegate.getActiveFileName());
        }

        // The asynchronous action is for compressing, we don't need to hook here
        @Override public Action getAsynchronous() {
            return delegate.getAsynchronous();
        }
    }

    public RolloverDescription rollover(final RollingFileManager manager) {
        RolloverDescription ret = super.rollover(manager);
        return new MyRolloverDescription(ret);
    }
}

如果我发布了 feature request，那么在 log4j2 的 future 版本中解决这个要求可能会更容易将实现。