Process Id in Logback Logging Pattern

Question

I have the following logback pattern:

<pattern>
    {"hostname": "${HOSTNAME}", 
     "level": "%p", 
     "method": "%M", 
     "process_id": "${process}", 
     "thread_id": "%t", 
     "timestamp": "%d{Y-M-d}T%d{H:M:S.s}", 
     "mesg":"%msg"}%n
</pattern>

Unfortunately when the log messages are actually generated I see: "process_id": "process_IS_UNDEFINED"

Is there any automatically set variable for process id, such as there is for hostname? I am having a lot of trouble finding a documented list of such automatically set variables in the logback documentation, does anyone know of a better documentation source?

Edit: I am aware of Mapped Diagnostic Contexts, but was hoping for a builtin solution that does not need such setup, much like how hostname works.

Answer 1

You can solve your problem with Mapped Diagnostic Context:

import org.slf4j.MDC;

public class Main {
    public static void main(String... args) {
        // put process ID early
        MDC.put("process_id", 
            ManagementFactory.getRuntimeMXBean().getName());
    }
}

After that all you need is to re-define your pattern as follows:

<pattern>{..., "process_id": "%X{process_id}"}</pattern>

EDITED

Also you can create your own encoder and converter and use them in logback.xml:

import ch.qos.logback.classic.PatternLayout;
import ch.qos.logback.classic.encoder.PatternLayoutEncoder;

public class ExtendedPatternLayoutEncoder extends PatternLayoutEncoder {
    @Override
    public void start() {
        // put your converter
        PatternLayout.defaultConverterMap.put(
            "process_id", ProcessIdConverter.class.getName());
        super.start();
    }
}

import ch.qos.logback.classic.pattern.ClassicConverter;
import ch.qos.logback.classic.spi.ILoggingEvent;

import java.lang.management.ManagementFactory;

public class ProcessIdConverter extends ClassicConverter {
    private static final String PROCESS_ID =
            ManagementFactory.getRuntimeMXBean().getName();

    @Override
    public String convert(final ILoggingEvent event) {
        // for every logging event return processId from mx bean
        // (or better alternative)
        return PROCESS_ID;
    }
}

<encoder class="some.package.ExtendedPatternLayoutEncoder">
    <pattern>{..., "process_id": "%process_id"}</pattern>
</encoder>

Full example:

    <encoder class="some.package.ExtendedPatternLayoutEncoder">
        <pattern>%d{dd.MM.yyyy HH:mm:ss.SSS} PID:%process_id [%thread] %-5level %logger{36} - %msg%n</pattern>
    </encoder>