Chain of Responsibility Pattern（譯）

責任鏈模式

責任鏈模式顧名思義，對於一個請求會去建立一條接受者鏈。這種模式會解耦一種類型的請求中接受者和發送者，該模式模式屬於行爲模式的一種。
在該模式當中，通常狀況下，每一個接受者都會有另一個接受者的引用，若是該接受者沒法處理該請求，請求會經過引用傳入下一個接受者。

實現

咱們建立一個抽象類AbstaractLogger，該類中含有日誌的記錄等級。而後咱們會建立三個logger實現AbstractLogger。每個logger都會檢查而且比較消息的等級與該logger等級，判斷打印或者不打印，而且傳遞消息到下一個logger。

第一步

建立一個抽象的Logger類

AbstractLogger.java

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

   protected int level;

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

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

第二步

建立具體的類實現AtstractLogger

ConsoleLogger.java

public class ConsoleLogger extends AbstractLogger {

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

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

ErrorLogger.java

public class ErrorLogger extends AbstractLogger {

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

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

FileLogger.java

public class FileLogger extends AbstractLogger {

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

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

第三步

建立不一樣類型的logger。設置每一個Logger的錯誤等級以及每一個logger的Next logger，每個logger的NextLogger都是當前鏈的一部分。

ChainPatternDemo.java

public 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;    
   }

   public 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.");
   }
}

第四步

校驗輸出

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.