责任链模式概念
避免请求发送者与接收者耦合在一起，让多个对象都有可能接收请求，将这些对象连接成一条链，并且沿着这条链传递请求，直到有对象处理它为止。
应用场景
- 有多个对象可以处理同一个请求，具体哪个对象处理该请求由运行时刻自动确定
- 在不明确指定接收者的情况下，向多个对象中的一个提交一个请求
- 可动态指定一组对象处理请求
实现案例
- 创建抽象的记录器类。 ``` java public abstract class AbstractLogger { public static int INFO = 1; public static int DEBUG = 2; public static int ERROR = 3;
protected int level;
//责任链中的下一个元素 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);
}
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- 创建扩展了该记录器类的实体类。
``` 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类：
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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类：
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public class FileLogger extends AbstractLogger { public FileLogger(int level){ this.level = level; } @Override protected void write(String message) { System.out.println("File::Logger: " + message); } }
- 创建不同类型的记录器。
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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."); } }