how to add an extra string or key/value pair only for some specific log message in java spring boot project

Question

In my spring boot application, we need to add an extra tag( key/value pair) only for some specific log messages to highlight that these are some special purpose logs and not for others.

Project log4j2.xml configuration:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
   <Appenders>
        <Console name="console" target="SYSTEM_OUT">
          <JsonTemplateLayout eventTemplateUri="classpath:LogstashLayout.json">
          </JsonTemplateLayout>
        </Console>
    </Appenders>
   <Loggers>
      <AsyncRoot level="info" additivity="false">
         <AppenderRef ref="console" />
      </AsyncRoot>
   </Loggers>
</Configuration>

What is the standard recommended approach to do this? is this need to be done some sort of filter configurations?

Answer 1

Think that marker would be helpful to you although it can just tag a log message but cannot add a key/value to it. After you use it to tag the log messages , you can configure a filter in the configuration to determine whether a message with certain tag should be displayed or not.

For example, you can tag the log messages something like:

public class Foo {

    private static final Marker TAG1 = MarkerManager.getMarker("TAG1");
    private static final Marker TAG2 = MarkerManager.getMarker("TAG2");
    private static final Marker TAG3 = MarkerManager.getMarker("TAG3");

    void test(){

        log.info(TAG1, "message with tag1");
        log.info(TAG1, "message with tag1");
        log.info(TAG2, "message with tag2");
        log.info(TAG2, "message with tag2");
        log.info(TAG3, "message with tag3");
        log.info(TAG3, "message with tag3");

    }
}

Then with this filter configuration :

  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
      <PatternLayout pattern="%d{ISO8601} |%t| %5p | %c{1} | %L | %m%n" />
      <Filters>
        <MarkerFilter marker="TAG1" onMatch="ACCEPT" onMismatch="NEUTRAL"/>
        <MarkerFilter marker="TAG2" onMatch="ACCEPT" onMismatch="NEUTRAL"/>
        <MarkerFilter marker="TAG3" onMatch="DENY" onMismatch="NEUTRAL"/>
      </Filters>>
    </Console>
  </Appenders>

Only messages with TAG1 , TAG2 and no tags will be displayed to console. Messages with TAG3 will not.

And if the filter configuration is :

  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
      <PatternLayout pattern="%d{ISO8601} |%t| %5p | %c{1} | %L | %m%n" />
      <Filters>
        <MarkerFilter marker="TAG1" onMatch="ACCEPT" onMismatch="NEUTRAL"/>
        <MarkerFilter marker="TAG2" onMatch="ACCEPT" onMismatch="NEUTRAL"/>
        <MarkerFilter marker="TAG3" onMatch="DENY" onMismatch="DENY"/>
      </Filters>>
    </Console>
  </Appenders>

Then only messages with TAG1 , TAG2 will be displayed. Messages with TAG3 or no tags will not.

The filter can be configured at the logger level or appender level. And I found this answer is helpful to understand the basic idea of how does the filter works.