设计模式

责任链模式

Posted by Laiaike on 2022-11-20

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，通常每个接收者都包含对另一个接收者的引用，请求沿着这条链进行处理。

  • 应用实例：jsp servlet 的 Filter，JAVA WEB 中 Apache Tomcat 对 Encoding 的处理，JS 中的事件冒泡。

实现

  1. 创建抽象类AbstractLogger。
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public class AbstractLogger {
    public static final Integer ERROR_LEVEL = 3; 
    public static final Integer DEBUG_LEVEL = 2; 
    public static final Integer INFO_LEVEL = 1; 

    protected Integer level;
    protected AbstractLogger nextAbstractLogger;

    public void setNextAbstractLogger(AbstractLogger nextAbstractLogger) {
        this.nextAbstractLogger = nextAbstractLogger;
    }

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

    public void write(String message) {

    }
}
  1. 创建三种不同等级的日志实体类，扩展AbstractLogger。
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public class ErrorLogger extends AbstractLogger{

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

    @Override
    public void write(String message) {
        System.out.println("ErrorLogger:" + message);
    }
}
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public class DebugLogger extends AbstractLogger{

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

    @Override
    public void write(String message) {
        System.out.println("DebugLogger:" + message);
    }
}
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public class InfoLogger extends AbstractLogger{

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

    @Override
    public void write(String message) {
        System.out.println("InfoLogger:" + message);
    }
}
  1. 创建不同级别的Logger，并指定每个Logger的下一个Logger。
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public class ChainPatternDemo {
    private static AbstractLogger getChainOfLoggers() {
        AbstractLogger errorLogger = new ErrorLogger(AbstractLogger.ERROR_LEVEL);
        AbstractLogger debugLogger = new DebugLogger(AbstractLogger.DEBUG_LEVEL);
        AbstractLogger infoLogger = new InfoLogger(AbstractLogger.INFO_LEVEL);

        errorLogger.setNextAbstractLogger(debugLogger);
        debugLogger.setNextAbstractLogger(infoLogger);

        return errorLogger;
    }

    public static void main(String[] args) {
        AbstractLogger chainOfLoggers = getChainOfLoggers();
        chainOfLoggers.logMessage(AbstractLogger.ERROR_LEVEL, "This is a log.");
        chainOfLoggers.logMessage(AbstractLogger.DEBUG_LEVEL, "This is a log.");
        chainOfLoggers.logMessage(AbstractLogger.INFO_LEVEL, "This is a log.");
    }
}

结果

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ErrorLogger:This is a log.
DebugLogger:This is a log.
InfoLogger:This is a log.
DebugLogger:This is a log.
InfoLogger:This is a log.
InfoLogger:This is a log.
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