log4cplus 的configure.h 中注释如下：
/**
* Read configuration from a file. <b>The existing configuration is
* not cleared nor reset.</b> If you require a different behavior,
* then call {@link BasicConfigurator#resetConfiguration
* resetConfiguration} method before calling
* <code>doConfigure</code>.
*
* <p>The configuration file consists of statements in the format
* <code>key=value</code>. The syntax of different configuration
* elements are discussed below.
*
* <h3>Appender configuration</h3>
*
* <p>Appender configuration syntax is:
* <pre>
* # For appender named <i>appenderName</i>, set its class.
* # Note: The appender name can contain dots.
* log4cplus.appender.appenderName=fully.qualified.name.of.appender.class
*
* # Set appender specific options.
* log4cplus.appender.appenderName.option1=value1
* ...
* log4cplus.appender.appenderName.optionN=valueN
* </pre>
*
* For each named appender you can configure its {@link Layout}. The
* syntax for configuring an appender's layout is:
* <pre>
* log4cplus.appender.appenderName.layout=fully.qualified.name.of.layout.class
* log4cplus.appender.appenderName.layout.option1=value1
* ....
* log4cplus.appender.appenderName.layout.optionN=valueN
* </pre>
*
* <h3>Configuring loggers</h3>
*
* <p>The syntax for configuring the root logger is:
* <pre>
* log4cplus.rootLogger=[LogLevel], appenderName, appenderName, ...
* </pre>
*
* <p>This syntax means that an optional <em>LogLevel value</em> can
* be supplied followed by appender names separated by commas.
*
* <p>The LogLevel value can consist of the string values FATAL,
* ERROR, WARN, INFO, DEBUG or a <em>custom LogLevel</em> value.
*
* <p>If a LogLevel value is specified, then the root LogLevel is set
* to the corresponding LogLevel. If no LogLevel value is specified,
* then the root LogLevel remains untouched.
*
* <p>The root logger can be assigned multiple appenders.
*
* <p>Each <i>appenderName</i> (separated by commas) will be added to
* the root logger. The named appender is defined using the
* appender syntax defined above.
*
* <p>For non-root loggers the syntax is almost the same:
* <pre>
* log4cplus.logger.logger_name=[LogLevel|INHERITED], appenderName, appenderName, ...
* </pre>
*
* <p>The meaning of the optional LogLevel value is discussed above
* in relation to the root logger. In addition however, the value
* INHERITED can be specified meaning that the named logger should
* inherit its LogLevel from the logger hierarchy.
*
* <p>By default loggers inherit their LogLevel from the
* hierarchy. However, if you set the LogLevel of a logger and
* later decide that that logger should inherit its LogLevel, then
* you should specify INHERITED as the value for the LogLevel value.
*
* <p>Similar to the root logger syntax, each <i>appenderName</i>
* (separated by commas) will be attached to the named logger.
*
* <p>See the <a href="http://www.cnblogs.com/http://www.cnblogs.com/manual.html#additivity">appender
* additivity rule</a> in the user manual for the meaning of the
* <code>additivity</code> flag.
*
* <p>The user can override any of the {@link
* Hierarchy#disable} family of methods by setting the a key
* "log4cplus.disableOverride" to <code>true</code> or any value other
* than false. As in <pre>log4cplus.disableOverride=true </pre>
*
* <h3>Example</h3>
*
* <p>An example configuration is given below.
*
* <pre>
*
* # Set options for appender named "A1".
* # Appender "A1" will be a SyslogAppender
* log4cplus.appender.A1=log4cplus::SyslogAppender
*
* # The syslog daemon resides on www.abc.net
* log4cplus.appender.A1.SyslogHost=www.abc.net
*
* # A1's layout is a PatternLayout, using the conversion pattern
* # <b>%r %-5p %c{2} %M.%L %x - %m\n</b>. Thus, the log output will
* # include # the relative time since the start of the application in
* # milliseconds, followed by the LogLevel of the log request,
* # followed by the two rightmost components of the logger name,
* # followed by the callers method name, followed by the line number,
* # the nested disgnostic context and finally the message itself.
* # Refer to the documentation of {@link PatternLayout} for further information
* # on the syntax of the ConversionPattern key.
* log4cplus.appender.A1.layout=log4cplus::PatternLayout
* log4cplus.appender.A1.layout.ConversionPattern=%-4r %-5p %c{2} %M.%L %x - %m\n
*
* # Set options for appender named "A2"
* # A2 should be a RollingFileAppender, with maximum file size of 10 MB
* # using at most one backup file. A2's layout is TTCC, using the
* # ISO8061 date format with context printing enabled.
* log4cplus.appender.A2=log4cplus::RollingFileAppender
* log4cplus.appender.A2.MaxFileSize=10MB
* log4cplus.appender.A2.MaxBackupIndex=1
* log4cplus.appender.A2.layout=log4cplus::TTCCLayout
* log4cplus.appender.A2.layout.ContextPrinting=enabled
* log4cplus.appender.A2.layout.DateFormat=ISO8601
*
* # Root logger set to DEBUG using the A2 appender defined above.
* log4cplus.rootLogger=DEBUG, A2
*
* # Logger definitions:
* # The SECURITY logger inherits is LogLevel from root. However, it's output
* # will go to A1 appender defined above. It's additivity is non-cumulative.
* log4cplus.logger.SECURITY=INHERIT, A1
* log4cplus.additivity.SECURITY=false
*
* # Only warnings or above will be logged for the logger "SECURITY.access".
* # Output will go to A1.
* log4cplus.logger.SECURITY.access=WARN
*
*
* # The logger "class.of.the.day" inherits its LogLevel from the
* # logger hierarchy. Output will go to the appender's of the root
* # logger, A2 in this case.
* log4cplus.logger.class.of.the.day=INHERIT
* </pre>
*
* <p>Refer to the <b>setOption</b> method in each Appender and
* Layout for class specific options.
*
* <p>Use the <code>#</code> character at the beginning of a line for comments.
*/
log4cplus.rootLogger=[LogLevel], appenderName, appenderName, ...
//配置 rootlogger [LogLevel] 有如下几种格式：FATAL, ERROR, WARN, INFO, DEBUG，TRACE