LOGMGR-182 support for logging complete MDC map

[jpraet]

When using %X in the log pattern without any key arguments, the complete
MDC map is now logged in format {key1=value1, key2=value2}.

[jpraet]

Or would it be better to use JSON format?

{"key1":"value1", "key2":"value2"}

There is no real established convention at the moment:

• logback: key1=val1, key2=val2
• log4j 1.2: {{key1,val1},{key2,val2}}
• log4j 2: {key1=value1, key2=value2}

[jpraet]

Any chance of this getting merged? I'm using a custom PatternFormatter at the moment to work around this:

public class MdcExpandingPatternFormatter extends PatternFormatter {

	private static final Pattern EXPAND_MDC = Pattern.compile("%X(?!\\{)");

	private static final String MDC_KEY = "MDC";

	private boolean expandMdc = false;

	@Override
	public void setPattern(String pattern) {
		Matcher matcher = EXPAND_MDC.matcher(pattern);
		if (matcher.find()) {
			super.setPattern(matcher.replaceFirst("%X{" + MDC_KEY + "}"));
			this.expandMdc = true;
		} else {
			super.setPattern(pattern);
		}
	}

	@Override
	public String format(ExtLogRecord record) {
		if (expandMdc) {
			Map<String, String> mdc = record.getMdcCopy();
			mdc.remove(MDC_KEY);
			record.putMdc(MDC_KEY, mdc.toString());
		}
		return super.format(record);
	}

}

[fs-aikito]

I'd be interested in this, and could use the workaround too. How do I use that custom formatter? The documentation on formatters seems bit sparse... I'm using wildfly-swarm if that matters. I tried just copy-pasting the code in my project, but it didn't get picked up automatically, do I need to register it somewhere somehow?

[jpraet]

We configured it like this in the jboss standalone.xml:

<formatter name="PATTERN">
    <custom-formatter module="be.fgov.kszbcss.tracer" class="be.fgov.kszbcss.log.formatter.MdcExpandingPatternFormatter">
        <properties>
            <property name="pattern" value="%d{yyyy-MM-dd HH:mm:ss,SSS} %-5p [%c] (%t) %X %s%e%n"/>
        </properties>
    </custom-formatter>
</formatter>

The custom formatter class was put in a shared global module. Don't know if/how that would work in wildfly-swarm.

[jamezp]

This should make it into WildFly 14.