class Logging::Layout

The Layout class provides methods for formatting log events into a string representation. Layouts are used by Appenders to format log events before writing them to the logging destination.

All other Layouts inherit from this class which provides stub methods. Each subclass should provide a format method. A layout can be used by more than one Appender so all the methods need to be thread safe.

Public Class Methods

new( :format_as → :string ) click to toggle source

Creates a new layout that will format objects as strings using the given :format_as style. This can be one of :string, :inspect, or :yaml. These formatting commands map to the following object methods:

  • :string => to_s

  • :inspect => inspect

  • :yaml => to_yaml

If the format is not specified then the global object format is used (see Logging#format_as). If the global object format is not specified then :string is used.

# File lib/logging/layout.rb, line 30
def initialize( opts = {} )
  ::Logging.init unless ::Logging.const_defined? :MAX_LEVEL_LENGTH

  default = ::Logging.const_defined?('OBJ_FORMAT') ?
            ::Logging::OBJ_FORMAT : nil

  f = opts.getopt(:format_as, default)
  f = f.intern if f.instance_of? String

  @obj_format = case f
                when :inspect, :yaml; f
                else :string end

  b = opts.getopt(:backtrace, ::Logging.backtrace)
  @backtrace = case b
      when :on, 'on', true;    true
      when :off, 'off', false; false
      else
        raise ArgumentError, "backtrace must be true or false"
      end
end

Public Instance Methods

format( event ) click to toggle source

Returns a string representation of the given logging event. It is up to subclasses to implement this method.

# File lib/logging/layout.rb, line 58
def format( event ) nil end
format_obj( obj ) click to toggle source

Return a string representation of the given object. Depending upon the configuration of the logger system the format will be an inspect based representation or a yaml based representation.

# File lib/logging/layout.rb, line 82
def format_obj( obj )
  case obj
  when String; obj
  when Exception
    str = "<#{obj.class.name}> #{obj.message}"
    if @backtrace && !obj.backtrace.nil?
      str << "\n\t" << obj.backtrace.join("\n\t")
    end
    str
  when nil; "<#{obj.class.name}> nil"
  else
    str = "<#{obj.class.name}> "
    str << case @obj_format
           when :inspect; obj.inspect
           when :yaml; try_yaml(obj)
           else obj.to_s end
    str
  end
end
header click to toggle source

Returns a header string to be used at the beginning of a logging appender.

# File lib/logging/layout.rb, line 66
def header( ) '' end
try_yaml( obj ) click to toggle source

Attempt to format the obj using yaml, but fall back to inspect style formatting if yaml fails.

# File lib/logging/layout.rb, line 108
def try_yaml( obj )
  "\n#{obj.to_yaml}"
rescue TypeError
  obj.inspect
end