CODEWITHSUNDEEP
javalogginglog4jlog4j2uuid
Durga Swaroop
Durga Swaroop

Reputation: 583

How to generate UUID per message in log4j's JSON Layout?

I need to generate a random string for a correlation key for each log message and I found that there is a way to generate UUID in log4j configuration file. There is a mention of UUID on https://logging.apache.org/log4j/2.x/manual/layouts.html, but it doesn't say anything about how to use it.

I am trying to set this as a value for a key in my JsonLayout. 

appender.rolling.layout.external-correlation-id.type = KeyValuePair
appender.rolling.layout.external-correlation-id.key = external-correlation-id
appender.rolling.layout.external-correlation-id.value = %u{"RANDOM"}

But that doesn't do anything. It just adds the literal string in the log message ... "external-correlation-id":"%u{\"RANDOM\"}" ....

How can I get a random string to set it in the log message? Is there a way for me to atleast directly call the UUID.randomUUID() in thelog4j properties file?

I don't want to use MDC for this and am looking for a way to do it directly from the log4j configuration file.

Any other help with this will be very appreciated.

Upvotes: 2

Views: 1809

Answers (1)

Michael Williams
Michael Williams

Reputation: 391

I've done something similar in a JsonLayout in a KeyValuePair using a custom StrLookup.

The code below shows a simple example of returning a UUID every time a message is logged using a custom Lookup. One would add the ability to have different operations per key etc. but this works.

import java.util.UUID;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.lookup.StrLookup;

@Plugin(name = "dyn", category = "Lookup")
public class DynamicLookup implements StrLookup {
  @Override
  public String lookup(String key) {
    if("uuid".equals(key)) {
      return UUID.randomUUID().toString();
    } else {
      return null;
    }
  }

  @Override
  public String lookup(LogEvent event, String key) {
    if("uuid".equals(key)) {
      return UUID.randomUUID().toString();
    } else {
      return null;
    }
  }
}

Then reference the Lookup using double $$ to have the value evaluated every message instead of just once.

<KeyValuePair key="event_id" value="$${dyn:uuid:-}"/>

Upvotes: 3

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