Pattern rendering

You can configure rendering using a pattern, like pattern layouts for Log4j and Logback. Pattern rendering is best suited to console output.

You can specify a pattern using the configuration DSL, for example:

  sink(
      "console",
      RenderPattern("%t{LOCAL_TIME} %-5v{COLOUR} [%-10c] - %30l - %m - %i%s"),
      STDOUT
  )
  // etc.

Here is a JSON configuration example:

{
  "sinks": {
    "console": {
      "renderPattern": "%t{LOCAL_TIME} %-5v{COLOUR} [%-10c] - %30l - %m - %i%s",
      "sendTo": "STDOUT"
    }
  }
  // etc.
}

Pattern language

Patterns contain:

• Fixed text that is included in every output.
• Tokens representing log event fields with optional size specification. Some tokens can be followed by a format specifier. Examples are %t, %-10l and %-5v{COLOUR}.

Tokens

The pattern language includes the following fields, each specified using % and a single letter:

Token	Field	Notes
%t	Timestamp	Default format is ISO8601, e.g. 2024-11-25T05:52:15.286632Z.
%h	Host
%l	Logger name
%c	Context
%v	Logging level
%m	Log message	If the message is a template, it is evaluated before being output.
%s	Stack trace	Only output if present, preceded by a newline.
%i	Items
%n	Newline	Output a single newline character.

Size specification

A size specification is put between % and the token letter. It is used to fit the field value into a fixed width, either left-or right aligned.

Zero

• Show the field value full width, the same as omitting the size specification.

Positive

• If the field value is longer than the size, maybe shorten it (see below) and show the left-most characters.
• If the value is shorter, left-align it in the width specified by the size.
• For stack traces, sets the maximum number of lines to show.

Negative

• If the field value is longer than the size, maybe shorten it (see below) and show the left-most characters.
• If the value is shorter, right-align it in the width specified by the size.

Notes:

• A size specification for the %n newline token is ignored.
• Host, logger name and context values are shortened if they are longer than the specified size.

Some example output from the pattern "%t{LOCAL_TIME} %-5v [%-20c] - %20l - %m - %i%2s" is:

16:55:45.014298  INFO [  D-worker-1+Playpen] - i.k.e.KloggerPlaypen - Event 3 at 2024-11-25T16:55:45.014279 - {run=ad085c84-35b2-4700-a57d-14a382d009a9, Counter=3, Iteration=3}
16:55:45.040453 ERROR [  D-worker-3+Playpen] - i.k.e.KloggerPlaypen - Message: Oops! Something went wrong - {run=ad085c84-35b2-4700-a57d-14a382d009a9, Message=Oops! Something went wrong}
java.lang.RuntimeException: Oops! Something went wrong
	at io.klogging.PlaypenKt.functionWithException(Playpen.kt:159)

Format specification

The %t and %v tokens can take a format specifier.

Format	Effect
%t{LOCAL_TIME}	Output only the time component of the event timestamp in the local timezone, instead of ISO8601 timestamp.
%v{COLOUR} or %v{COLOR}	Output log levels with a different colour for each level, as for RENDER_ANSI.

Level colours are (approximately):

• TRACE
• DEBUG
• INFO
• WARN
• ERROR
• FATAL

You can combine size and format specifications.