基本概念

為請求創(chuàng)建一個接收者對象的鏈，屬于行為型模式，在這種模式中，通常每個接收者都包含對另一個接收者的引用。如果一個對象不能處理該請求，那么它會把相同的請求傳給下一個接收者，依此類推

• 意圖: 請求的接收者形成一條鏈，沿著這個鏈傳遞請求
• 解決什么問題：將請求的發(fā)送者和請求的接收者進行解耦，請求的發(fā)送者只關心請求的發(fā)送，具體的處理流程不需要關心
• 何時使用：處理消息的時候需要過濾很多道
• 如何實現(xiàn)：攔截的類實現(xiàn)統(tǒng)一接口
• 應用場景：JavaWeb中的Filter JS中的事件冒泡

舉個例子

我們創(chuàng)建抽象類 AbstractLogger，帶有詳細的日志記錄級別。然后我們創(chuàng)建三種類型的記錄器，都擴展了 AbstractLogger。每個記錄器消息的級別是否屬于自己的級別，如果是則相應打印出來，否則將不打印并把消息傳給下一個記錄器

樣例類圖

//創(chuàng)建抽象logger
public abstract class AbstractLogger {
   public static int INFO = 1;
   public static int DEBUG = 2;
   public static int ERROR = 3;

   protected int level;

   //責任鏈中的下一個元素
   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);
    
}


//定義三個具體的logger類 重寫write方法
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);
   }
}

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);
   }
}

public class FileLogger extends AbstractLogger {

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

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



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.");
   }
}

程序輸出

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.

本文例子來自http://www.runoob.com/design-pattern/chain-of-responsibility-pattern.html