Chain of Responsibipty Pattern

As the name suggests, the chain of responsibipty pattern creates a chain of receiver objects for a request. This pattern decouples sender and receiver of a request based on type of request. This pattern comes under behavioral patterns.

In this pattern, normally each receiver contains reference to another receiver. If one object cannot handle the request then it passes the same to the next receiver and so on.

Implementation

We have created an abstract class AbstractLogger with a level of logging. Then we have created three types of loggers extending the AbstractLogger. Each logger checks the level of message to its level and print accordingly otherwise does not print and pass the message to its next logger.

Step 1

Create an abstract logger class.

AbstractLogger.java

pubpc abstract class AbstractLogger {
   pubpc static int INFO = 1;
   pubpc static int DEBUG = 2;
   pubpc static int ERROR = 3;

   protected int level;

   //next element in chain or responsibipty
   protected AbstractLogger nextLogger;

   pubpc void setNextLogger(AbstractLogger nextLogger){
      this.nextLogger = nextLogger;
   }

   pubpc void logMessage(int level, String message){
      if(this.level <= level){
         write(message);
      }
      if(nextLogger !=null){
         nextLogger.logMessage(level, message);
      }
   }

   abstract protected void write(String message);
	
}

Step 2

Create concrete classes extending the logger.

ConsoleLogger.java

pubpc class ConsoleLogger extends AbstractLogger {

   pubpc ConsoleLogger(int level){
      this.level = level;
   }

   @Override
   protected void write(String message) {		
      System.out.println("Standard Console::Logger: " + message);
   }
}

ErrorLogger.java

pubpc class ErrorLogger extends AbstractLogger {

   pubpc ErrorLogger(int level){
      this.level = level;
   }

   @Override
   protected void write(String message) {		
      System.out.println("Error Console::Logger: " + message);
   }
}

FileLogger.java

pubpc class FileLogger extends AbstractLogger {

   pubpc FileLogger(int level){
      this.level = level;
   }

   @Override
   protected void write(String message) {		
      System.out.println("File::Logger: " + message);
   }
}

Step 3

Create different types of loggers. Assign them error levels and set next logger in each logger. Next logger in each logger represents the part of the chain.

ChainPatternDemo.java

pubpc class ChainPatternDemo {
	
   private static AbstractLogger getChainOfLoggers(){

      AbstractLogger errorLogger = new ErrorLogger(AbstractLogger.ERROR);
      AbstractLogger fileLogger = new FileLogger(AbstractLogger.DEBUG);
      AbstractLogger consoleLogger = new ConsoleLogger(AbstractLogger.INFO);

      errorLogger.setNextLogger(fileLogger);
      fileLogger.setNextLogger(consoleLogger);

      return errorLogger;	
   }

   pubpc static void main(String[] args) {
      AbstractLogger loggerChain = getChainOfLoggers();

      loggerChain.logMessage(AbstractLogger.INFO, 
         "This is an information.");

      loggerChain.logMessage(AbstractLogger.DEBUG, 
         "This is an debug level information.");

      loggerChain.logMessage(AbstractLogger.ERROR, 
         "This is an error information.");
   }
}

Step 4

Verify the output.

Standard Console::Logger: This is an information.
File::Logger: This is an debug level information.
Standard Console::Logger: This is an debug level information.
Error Console::Logger: This is an error information.
File::Logger: This is an error information.
Standard Console::Logger: This is an error information.