10. Design Logging System | Chain of Responsibility Design Pattern | Amazon System Design interview 

there are folks in the comment section questioning if COR is the right pattern for logger or it can be done differently, here is my two cents on this, reason why chain of responsibility is the right pattern here: let's take example of log4j, we can enable certain log level in the system like ERROR or INFO etc, this is how the error levels are defined ALL < DEBUG < INFO < WARN < ERROR < FATAL < OFF e.g. if log level is set to warn, then only warn, error, fatal will be printed, rest all logs with other log levels will be disabled like debug, info etc will not be printed Now you can see that chain of responsibility comes in handy here, lets say I have used warn as log level in log 4j and in code i have different logs like debug, info, error etc lets take error, it will go to all handlers and check what log level is enabled e.g. it will first go to debug handler, is it enabled, no, then go to next info and next warn, okay warn is enabled but the log level to be printed is error, then it will move to next handler i.e. error okay now it matches the log level to be printed and also at the system level warn is enabled and error handler is eligible for printing this log There is a order of execution here where the request may or may not be fulfilled based on what log level is enabled and the order which the request should be served is defined by the chain of responsibility pattern i.e. ALL < DEBUG < INFO < WARN < ERROR < FATAL < OFF

This is where we actually implement a Linked List from scratch to solve a real world problem!! And this proves why understanding datastructures from scratch is important and not simply use library classes. Great video!! 💯

Spring Security Filter chain is the perfect example of this Design pattern in my opinion..where your authentication request goes through multiple Authentication Provider

How to decide when to use if-else / switch-case and when to use chain of responsibility pattern? Like in case of logger since we already know about all the handlers and the chain order in advance why not use if-else statement for each log level

Man , you're the best person for this content❤❤❤ . Definitely recommending this channel to many.

apki understanding bahot acchi hai. mujhe kafi benifit mila

Great Quality content with simple explanation. Thanks

first of all, doing great work. I have a suggestion that it should not be the responsibility of main method to invoke the info or debug logger rather the logProcessor should be responsible of creating the chain of log processors and main method just invoke the logger and then calls it for printing logs

idk but does this design pattern really helps? The problem it is trying to solve can be easily solved by data structure or even by if else conditions if levels are not too many. why i would want the flow to reach it to error via info or log when i can reach there directly? or in vending machine if i want water why do i want the flow go via pepsi or coke??

great example. Just one question, why can't we use switch case here to get exact match of that object type and call its method? if none is found, default case would return.

highly underrated playlist for System design interview prep.

First of all great content. I love watching your playlist. 1 question, why not enums & static vars?

Hey @shreyansh , can we also use factory pattern for logging as in the video itself the logging level can be determined using the type like info, debug or error and based on the type the implementing class can print the statement ? Just curious about the different approach in this logging specific problem. Although I understood the case where the rs 2000 were being fetched from ATM.

Very helpful video..Thank you for sharing your knowledge 👏👍

Hey just a question, why can't we have three different objects and use something like a factory pattern to dynamically select the object on basis of some string(info, debug or error) and then invoke that object's logging function. Why do we need to maintain a chain of responsibility

Why do we use abstract class instead of normal class in Responsibility chain design pattern, when we don't have any abstract methods inside it?

great video. one doubt is , cant we use simple factory pattern also to solve logger question ? based on log type in request, factory will return corresponding logger class and we will call log method in that class

how to decide whether to use factory or chain of responsbility principle in use cases like logger?

Brilliant content as always Keep it up Shrayansh

great explanation... thanks sir ji... though the video length is 15min only.. one might need to spend more time understanding how this chain is transferring their responsibilities to next chained object.

Hi Shrayansh, can you give the insights about logging mechanism in distributed micro-services in HLD video?

Awesome explanation. can you help me understand why we prefer this design pattern over just simple if/else in the base class to create different logger object? to avoid unnecessary iteration over complete list

Awsome content keeping posting

Given the number of log levels are fixed. A EnumMap with Map would have been faster and maintainable compared to chain of responsibility design pattern.

For the logger method, we could have simply used Factory design pattern to determine the correct logger as per the enum passed, why do we need a chain of responsibility pattern? In this scenario, why should an error message be even processed by InfoLogProcessor?

can this can be used for employee detail check scenario, say aadhar,pan,bank details checking one after one ??

in the main class we have made an nested initialization to the Logger class.But in actual production code there is no such nested initialization in Log4j sdk .How does that works internally then?

Thank you Awesome explanation :)) waiting for next one!

can logger be implemented with observer pattern as well..? Where an error been written to multiple type of file or console..?

I was recently asked in an interview to design multi tier LRU cache where each layer will have increasing size and time of retrieval. Can this be done using chain of responsibility considering if element is found, we need to populate it backwards in all previous layers for cache to be updated?

. This logger can be implemented by strategy design pattern or abstract design pattern also ri8 since based on loglevel type we are implementing respective class.. whats is the use of chain of processing in classes as we know which log level type need to be used..

This 1 was best

Hey! for this logger implementation can we not use factory design pattern where it can provide me the instance of logger based on the requirement ?

Hey . Like you said that vending machine can be designed by the state design pattern(in vending machine design video) and here you are saying that we can do this with chain of responsibility as well. I think ATM can also be designed by State design pattern . what do you think about it ?

Great

Can't we use a Factory pattern for logging? So, based on the LogLevel, we can return the corresponding object.

Thanks for the video. One doubt why can't we use the factory pattern here?

Whats the benefit of writing log processor class as abstract

awsomne

isn't State DP used to design Vending machines?

Loggers also come in singleton???

For a logger implementation, what is the actual difference between COR pattern and decorator pattern?

Why are we not using the factory design pattern?

For this kind of design, why can't we use Factory pattern? Factory can return the required kind of class based on log level, and then use that to print the log in proper format.

why can't we have different methods like logE, logI, logW?

binge watching to save myself from getting new membership next month . xD , but coding is taking time .

How to access car rental and car parking lot video ?

pls do english version

iska gitlab link nhi hai kya?

Where is the repo link? Pz send me here.

This could be simplified by using abstract method template with above implementation, so that you only care about how to log not when to log. The code would look like Your abstract Processor class would look like this: constructor(nextLogger) { .... } protected Logger nextLogger = null; public final void log(int logLevel, String message){.

Sir code not working for me it is going in infinite loop😢

Isn't this design bad. Suppose in future we create a new handler and they fail to implement next logic properly then the whole system goes for a toss.

Kindly allow access to all videos @ConceptAndCoding

But ATM/Vending machine to State design ka use krte h na??

May be more simple implementation package LLDQuestions.Logger.LoggerBasic; import java.io.IOException; import java.io.PrintWriter; enum LogLevel { INFO, WARNING, ERROR } interface LogSink { void log(String message); } class ConsoleSink implements LogSink { @Override public void log(String message) { System.out.println(message); } } class FileSink implements LogSink { private String filename; public FileSink(String filename) { this.filename = filename; } @Override public void log(String message) { try (PrintWriter writer = new PrintWriter(filename)) { writer.println(message); } catch (IOException e) { e.printStackTrace(); } } } class Logger { private LogLevel logLevel; private LogSink logSink; public Logger(LogLevel logLevel, LogSink logSink) { this.logLevel = logLevel; this.logSink = logSink; } public void log(LogLevel level, String message) { if (level.ordinal() >= logLevel.ordinal()) { String logMessage = "[" + level + "] " + message; logSink.log(logMessage); } } } public class Solution { public static void main(String[] args) { LogSink consoleSink = new ConsoleSink(); LogSink fileSink = new FileSink("log.txt"); Logger consoleLogger = new Logger(LogLevel.INFO, consoleSink); Logger fileLogger = new Logger(LogLevel.WARNING, fileSink); consoleLogger.log(LogLevel.INFO, "This is an info message"); consoleLogger.log(LogLevel.WARNING, "This is a warning message"); fileLogger.log(LogLevel.ERROR, "This is an error message"); } }