责任链模式

责任链模式

责任链模式（Chain of Responsibility Pattern）为请求创建了一个接收者对象的链。

使用场景： 1、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。 2、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。 3、可动态指定一组对象处理请求。

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1、创建抽象日志类

public abstract class AbstractLogger {
    public static int info = 1;
    public static int debug = 2;
    public static int error = 3;

    protected int level;

    protected AbstractLogger nextLogger;

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

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

    protected abstract  void  write(String Message);
}

2、创建扩展了该抽象日志类的实体类

public class ConsoleLogger extends AbstractLogger {
     public ConsoleLogger(int level){
         this.level = level;
     }
    @Override
    protected void write(String Message) {
        System.out.println("Console log:" + Message);
    }
}

public class DebugLogger extends AbstractLogger {
    public DebugLogger(int level){
        this.level = level;
    }
    @Override
    protected void write(String Message) {
        System.out.println("Debug log:"+ Message);
    }
}

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

    @Override
    protected void write(String Message) {
        System.out.println("Error logger:"+Message);
    }
}

3、测试类

public class ChainPatternDemo {
    public static void main(String[] args) {
        AbstractLogger loggerChain = getChainLogger();
        loggerChain.logMessage(AbstractLogger.info,"This is an information.");
        loggerChain.logMessage(AbstractLogger.debug,"This is debug information.");
        loggerChain.logMessage(AbstractLogger.error,"This is error information.");
    }

    private static AbstractLogger getChainLogger() {
        AbstractLogger consoleLogger = new ConsoleLogger(AbstractLogger.info);
        AbstractLogger debugLogger = new DebugLogger(AbstractLogger.debug);
        AbstractLogger errorLogger = new ErrorLogger(ErrorLogger.error);

        errorLogger.setNextLogger(debugLogger);
        debugLogger.setNextLogger(consoleLogger);

        return errorLogger;
    }
}

4、运行状态

当运行loggerChain.logMessage(AbstractLogger.error,"This is error information.")时

5、测试结果

Console log:This is an information.
Debug log:This is debug information.
Console log:This is debug information.
Error logger:This is error information.
Debug log:This is error information.
Console log:This is error information.