Configuration Samples

The following snippets show various ways of configuring log4cxx.

Patterns

The basic way of outputing messages is by using a [PatternLayout](@ref log4cxx.PatternLayout), and then sending the messages to stderr/stdout/file. The following examples show how you might configure the PatternLayout in order to achieve the results shown.

Each example has two blocks of code: the layout for the PatternLayout, and a sample output message.

Pattern 1

This pattern contains the date in an ISO-8601 format(without fractional seconds), followed by the logger name, the level, and then the message.

[%d{yyyy-MM-dd HH:mm:ss}] %c %-5p - %m%n

[2020-12-24 15:31:46] root INFO  - Hello there!

Pattern 2

Similar to Pattern 1, except using ISO-8601 with fractional seconds

[%d] %c %-5p - %m%n

[2020-12-24 15:35:39,225] root INFO  - Hello there!

Pattern 3

Prints out the number of milliseconds since the start of the application, followed by the level(5 character width), followed by the logger name (20 character width), followed by the message.

%r %-5p %-20c %m%n

0 INFO  root                 Hello there!

XML Files

One way of configuring log4cxx is with XML files. The following are some examples on various ways of using an XML file to configure the logging.

XML Example 1

This simple example simply writes messages to stdout. If you want to send messages to stderr instead, simply change the ‘Target’ value to System.err.

<?xml version="1.0" encoding="UTF-8" ?>
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

  <appender name="ConsoleAppender" class="org.apache.log4j.ConsoleAppender">
    <param name="Target" value="System.out"/>
    <layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="%m%n"/>
    </layout>
  </appender>

  <root>
     <priority value="info" />
     <appender-ref ref="ConsoleAppender"/>
  </root>

</log4j:configuration>

Sample output:

Hello there!

XML Example 2

This example sends data to both stdout, as well as to a file. In this case, the file will be in our working directory. The pattern has also been updated to match with pattern example 1

<?xml version="1.0" encoding="UTF-8" ?>
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

  <appender name="ConsoleAppender" class="org.apache.log4j.ConsoleAppender">
    <param name="Target" value="System.out"/>
    <layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="[%d{yyyy-MM-dd HH:mm:ss}] %c %-5p - %m%n"/>
    </layout>
  </appender>

  <appender name="FileAppender" class="org.apache.log4j.FileAppender">
    <param name="file" value="example.log" />
    <layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="[%d{yyyy-MM-dd HH:mm:ss}] %c %-5p - %m%n" />
    </layout>
  </appender>

  <root>
     <priority value="info" />
     <appender-ref ref="ConsoleAppender"/>
     <appender-ref ref="FileAppender"/>
  </root>

</log4j:configuration>

Sample output:

[2020-12-24 15:57:35] root INFO  - Hello there!

XML Example 3

This example shows how you can configure logging for a particular category.

Assume that our loggers are in our code as such:

	log4cxx::LoggerPtr root = log4cxx::Logger::getRootLogger();
	log4cxx::LoggerPtr com  = log4cxx::Logger::getLogger( "com" );
	log4cxx::LoggerPtr com_example = log4cxx::Logger::getLogger( "com.example" );

	LOG4CXX_INFO( root, "Hello there!" );
	LOG4CXX_DEBUG( com, "com logger debug" );
	LOG4CXX_DEBUG( com_example, "com.example debug message" );
	LOG4CXX_TRACE( com, "com debug message" );
	LOG4CXX_TRACE( com_example, "com.example trace message" );

For this configuration, we have set any logger that is at the com level or below to be debug. However, we have also set the logger com.example to have a more verbose trace level to see more information from that particular logger.

<?xml version="1.0" encoding="UTF-8" ?>
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

  <appender name="ConsoleAppender" class="org.apache.log4j.ConsoleAppender">
    <param name="Target" value="System.out"/>
    <layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="[%d{yyyy-MM-dd HH:mm:ss}] %c %-5p - %m%n"/>
    </layout>
  </appender>

  <appender name="FileAppender" class="org.apache.log4j.FileAppender">
    <param name="file" value="example.log" />
    <layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="[%d{yyyy-MM-dd HH:mm:ss}] %c %-5p - %m%n" />
    </layout>
  </appender>

  <root>
     <priority value="info" />
     <appender-ref ref="ConsoleAppender"/>
     <appender-ref ref="FileAppender"/>
  </root>

  <logger name="com" >
     <priority value="debug"/>
  </logger>

  <logger name="com.example" >
     <priority value="trace"/>
  </logger>

</log4j:configuration>

Sample output:

[2020-12-24 16:05:48] root INFO  - Hello there!
[2020-12-24 16:05:48] com DEBUG - com logger debug
[2020-12-24 16:05:48] com.example DEBUG - com.example debug message
[2020-12-24 16:05:48] com.example TRACE - com.example trace message