Rantaian tanggungjawab

Seperti namanya, rantaian tanggungjawab mewujudkan rantaian objek penerima untuk mengendalikan permintaan.
Corak ini memisahkan pengirim dan penerima permintaan berdasarkan jenis permintaan.
Corak ini terdapat di bawah corak Gelagat.

Dalam corak ini setiap objek penerima permintaan mempunyai rujukan kepada objek seterusnya jika ia tidak dapat mengendalikan permintaan, permintaan itu diturunkan kepada penerima seterusnya dalam rantai.

Mari kita fahami ini dengan mengambil contoh mekanisme pengelogan yang merekodkan mesej berdasarkan tahap mesej (permintaan)

AbstractLogger

package Patterns.Behavioral.chainOfResponsibility;

public abstract class AbstractLogger{
    /**
     * TRACE < DEBUG < INFO < WARN < ERROR < FATAL
     * which means if the level is INFO, then INFO, WARN, ERROR and FATAL messages will be logged
     * but if the level is ERROR then only ERROR and FATAL messages will be logged 
    */
    //higher the number higher the priority
    public static int DEBUG = 1;
    public static int INFO = 2;
    public static int ERROR = 3;
    protected int LEVEL;
    //next Logger in the chain of responsibility
    private AbstractLogger nextLogger;
    public void setNextLogger(AbstractLogger logger){
        this.nextLogger = logger;
    }
    public void logMessage(int level, String message){
        //If the logging level of the message is greater than the current Logger's LEVEL then it will be logged 
        //example if level = ERROR and this.LEVEL = INFO then the message will be logged as INFO has a lower priority than ERROR
        if(this.LEVEL <=level){
            write(message);
        }
        // else the message/request will be passed down to the next logger/object in the chain
        else{
            if(nextLogger!=null){
                nextLogger.logMessage(level, message);
            }
        }
    }
    abstract void write(String message);
}

Pembalak Konkrit

package Patterns.Behavioral.chainOfResponsibility;

public class DebugLogger extends AbstractLogger {
    private String className = this.getClass().getSimpleName();
    private String logger   = "DEBUG";
    public DebugLogger(){
        this.LEVEL = 1;
    }

    @Override
    void write(String message) {
        System.out.println(className+":"+logger+":"+message);
    }

}

package Patterns.Behavioral.chainOfResponsibility;

public class InfoLogger extends AbstractLogger {
    private String className = this.getClass().getSimpleName();
    private String logger   = "INFO";
    public InfoLogger(){
        this.LEVEL = 2;
    }

    @Override
    void write(String message) {
        System.out.println(className+":"+logger+":"+message);
    }

}
package Patterns.Behavioral.chainOfResponsibility;

public class ErrorLogger extends AbstractLogger {
    private String className = this.getClass().getSimpleName();
    private String logger   = "ERROR";
    public ErrorLogger(){
        this.LEVEL = 3;
    }

    @Override
    void write(String message) {
        System.out.println(className+":"+logger+":"+message);
    }

}

Utama

package Patterns.Behavioral.chainOfResponsibility;

public class Main {
    public static AbstractLogger intializeLoggers(){
        AbstractLogger errorLogger = new ErrorLogger(); //LEVEL = 3;
        AbstractLogger infoLogger = new InfoLogger(); //LEVEL = 2;
        AbstractLogger debugLogger = new DebugLogger(); // LEVEL = 1;
        errorLogger.setNextLogger(infoLogger);
        infoLogger.setNextLogger(debugLogger);
        return errorLogger;// return the highest priority Logger first


    }
    public static void main(String args[]){
        // initialize the chain of responsible objects
        AbstractLogger logger  = intializeLoggers();

        //pass the request down the responsibility chain
        //logging level 3 logger
        logger.logMessage(3, "log this error message");
        //loggin level 2 logger
        logger.logMessage(2, "info level log message");
        //logging level 1 logger
        logger.logMessage(1, "debug level log message");
    }
}

Output:

ErrorLogger:ERROR:log this error message
InfoLogger:INFO:info level log message
DebugLogger:DEBUG:debug level log message

Isi penting

• Mengikut LSP (Prinsip penggantian Liskov iaitu corak reka bentuk pepejal).
• Mengikut SRP prinsip kukuh.
• Mengikut prinsip pepejal OCP kerana kami boleh menambah lebih banyak Logger seperti surih, maut, dll tanpa mengubah suai kod sedia ada sama sekali.
• Ikuti ISP juga.

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