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1 責(zé)任鏈模式

責(zé)任鏈模式（Chain of Responsibility Pattern）為請(qǐng)求創(chuàng)建了一個(gè)接收者對(duì)象的鏈。這種模式給予請(qǐng)求的類(lèi)型，對(duì)請(qǐng)求的發(fā)送者和接收者進(jìn)行解耦。這種類(lèi)型的設(shè)計(jì)模式屬于行為型模式。在這種模式中，通常每個(gè)接收者都包含對(duì)另一個(gè)接收者的引用。如果一個(gè)對(duì)象不能處理該請(qǐng)求，那么它會(huì)把相同的請(qǐng)求傳給下一個(gè)接收者，依此類(lèi)推。

2 優(yōu)點(diǎn)和缺點(diǎn)

職責(zé)鏈上的處理者負(fù)責(zé)處理請(qǐng)求，客戶只需要將請(qǐng)求發(fā)送到職責(zé)鏈上即可，無(wú)須關(guān)心請(qǐng)求的處理細(xì)節(jié)和請(qǐng)求的傳遞，所以職責(zé)鏈將請(qǐng)求的發(fā)送者和請(qǐng)求的處理者解耦了。

3 測(cè)試Demo類(lèi)圖

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

4 代碼實(shí)現(xiàn)

1） AbstractLogger.java

    public abstract class AbstractLogger {
       public static int INFO = 1;
       public static int DEBUG = 2;
       public static int ERROR = 3;
     
       protected int level;
     
       //責(zé)任鏈中的下一個(gè)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);
       
    }

2）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);
       }
    }

3）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);
       }
    }

4）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);
       }
    }

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

5 運(yùn)行結(jié)果

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

參考地址：https://www.runoob.com/design-pattern/chain-of-responsibility-pattern.html