Chain-of-responsibility pattern: Difference between revisions

Revision as of 09:58, 3 May 2023

Revision as of 10:05, 3 May 2023

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{{wikibooks|Computer Science Design Patterns|Chain of responsibility|Chain-of-responsibility implementations in various languages}}

=== Crystal example ===

<syntaxhighlight lang="crystal">

enum LogLevel

None

Info

Debug

Warning

Error

FunctionalMessage

FunctionalError

All

end

abstract class Logger

property log_levels

property next : Logger | Nil

def initialize(*levels)

@log_levels = [] of LogLevel

levels.each do |level|

@log_levels << level

end

end

def message(msg : String, severity : LogLevel)

if @log_levels.includes?(LogLevel::All) || @log_levels.includes?(severity)

write_message(msg)

end

@next.try(&.message(msg, severity))

end

abstract def write_message(msg : String)

end

class ConsoleLogger < Logger

def write_message(msg : String)

puts "Writing to console: #{msg}"

end

end

class EmailLogger < Logger

def write_message(msg : String)

puts "Sending via email: #{msg}"

end

end

class FileLogger < Logger

def write_message(msg : String)

puts "Writing to Log File: #{msg}"

end

end

# Program

# Build the chain of responsibility

logger = ConsoleLogger.new(LogLevel::All)

logger1 = logger.next = EmailLogger.new(LogLevel::FunctionalMessage, LogLevel::FunctionalError)

logger2 = logger1.next = FileLogger.new(LogLevel::Warning, LogLevel::Error)

# Handled by ConsoleLogger since the console has a loglevel of all

logger.message("Entering function ProcessOrder().", LogLevel::Debug)

logger.message("Order record retrieved.", LogLevel::Info)

# Handled by ConsoleLogger and FileLogger since filelogger implements Warning & Error

logger.message("Customer Address details missing in Branch DataBase.", LogLevel::Warning)

logger.message("Customer Address details missing in Organization DataBase.", LogLevel::Error)

# Handled by ConsoleLogger and EmailLogger as it implements functional error

logger.message("Unable to Process Order ORD1 Dated D1 For Customer C1.", LogLevel::FunctionalError)

# Handled by ConsoleLogger and EmailLogger

logger.message("Order Dispatched.", LogLevel::FunctionalMessage)

</syntaxhighlight>

Output

<pre>

Writing to console: Entering function ProcessOrder().

Writing to console: Order record retrieved.

Writing to console: Customer Address details missing in Branch DataBase.

Writing to Log File: Customer Address details missing in Branch DataBase.

Writing to console: Customer Address details missing in Organization DataBase.

Writing to Log File: Customer Address details missing in Organization DataBase.

Writing to console: Unable to Process Order ORD1 Dated D1 For Customer C1.

Sending via email: Unable to Process Order ORD1 Dated D1 For Customer C1.

Writing to console: Order Dispatched.

Sending via email: Order Dispatched.

</pre>

=== PHP example ===