编辑“︁Logging in Marauroa”︁（章节）

= Summary =

The simple description is that when writing code, a logger object is created in each class definition where logging is required. Each logger has several methods that relate to the importance (level) of a message to be logged. These are TRACE < DEBUG < INFO < WARN < ERROR < FATAL with TRACE being the lowest priority and FATAL the highest. A example might be:

<pre>
    logger.warn("This is a warning message");
</pre>

The behaviour of the logging is controlled by a configuration file. This specifies:
* The default (root) logging level and any output stream names (appenders)

For each appender:
* The type of appender, i.e. the output stream, e.g.
** ConsoleAppender, FileAppender, RollingFileAppender (and others)
* The format of the output
** PatternLayout, XMLLayout
* Any format specifiers, e.g. the layout of a pattern

For each class containing a logger (optional):
* The logger class and minimum level of message that will be logged, using the levels given above plus ALL and OFF. If a class is not listed it will use the root level specified above.

A sample configuration file might look like:

<pre>
# Set root logger level to INFO and its only appender to A1.
log4j.rootLogger=INFO, A1

# A1 is set to be a ConsoleAppender.
log4j.appender.A1=org.apache.log4j.ConsoleAppender

# A1 uses PatternLayout.
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n
</pre>

== Specify Configuration at runtime ==

Add the following parameters to the java command line when starting your program.

-Dlog4j.configuration="file:/C:/my/folder/log4j.properties"

-Dlog4j.debug