责任链模式

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顾名思义，责任链模式(Chain of Responsibility Pattern) 为请求创建了一个接收者对象的链。这种模式给予请求的类型，对请求的发送者和接收者进行解耦。这种类型的设计模式属于行为型模式。

责任链（Chain Of Responsibility）

Class Diagram

Implementation

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/**
 * Created with IntelliJ IDEA.
 * User: 长歌
 * Date: 2019/11/6
 * Description: 抽象日志组件
 */
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);
}


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

    protected void write(String message) {
        System.out.println("Standard Console::Logger: " + message);
    }
}


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

    protected void write(String message) {
        System.out.println("Error Console::Logger: " + message);
    }
}


public class FileLogger extends AbstractLogger {

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

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

/**
 * Created with IntelliJ IDEA.
 * User: 长歌
 * Date: 2019/11/6
 * Description: 日志工厂类
 */
public class LoggerFactroy {

    private LoggerFactroy(){}

    public static AbstractLogger getLogger(){
        AbstractLogger logger = new ErrorLogger(AbstractLogger.ERROR);
        AbstractLogger fileLogger = new FileLogger(AbstractLogger.DEBUG);
        AbstractLogger consoleLogger = new ConsoleLogger(AbstractLogger.INFO);

        logger.setNextLogger(fileLogger);
        fileLogger.setNextLogger(consoleLogger);
        return logger;
    }
}

测试类

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public class ChainOfResponsibilityPatternTest {

    @Test
    public void test() throws Exception {
        AbstractLogger logger = LoggerFactroy.getLogger();
        logger.logMessage(AbstractLogger.INFO, "This is an information.");

        logger.logMessage(AbstractLogger.DEBUG,
                "This is a debug level information.");

        logger.logMessage(AbstractLogger.ERROR,
                "This is an error information.");
    }
}

Example

  • [javax.servlet.Filter#doFilter()