Behavioral Patterns Part 1/11: Chain Of Responsibility Pattern

目录

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Definition

通过给每一个receiver有机会来接收request的方式避免了request的sender和receiver之间的耦合。

把接收对象链(chain)起来，然后沿着chain传递request，直到有对象处理它。

A method called in one class will move up a class hierarchy until a method is found that can properly handle the call.

何时使用？希望解耦sender和receiver，也就是request发送不用指定具体的receiver。

使用频率： Medium Low

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UML Class Diagram

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Implementation

这里考虑一个日志(Logger)的应用——

级别高的信息要在所有比此级别低的Logger中显示。

// AbstractLogger.javapackage designpatterns.behavioralpatterns.cor;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 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);}// SpecificLogger.javapackage designpatterns.behavioralpatterns.cor;class InfoLogger extends AbstractLogger {    public InfoLogger(int level) {        this.level = level;    }    @Override    protected void write(String message) {        System.out.println("Info Console::Logger: " + message);    }}class ErrorLogger extends AbstractLogger {    public ErrorLogger(int level) {        this.level = level;    }    @Override    protected void write(String message) {        System.out.println("Error Console::Logger: " + message);    }}class DebugLogger extends AbstractLogger {    public DebugLogger(int level) {        this.level = level;    }    @Override    protected void write(String message) {        System.out.println("Debug Console::Logger: " + message);    }}// CORDemo.javapackage designpatterns.behavioralpatterns.cor;public class CORDemo {
         private static AbstractLogger getChainOfLoggers() {        AbstractLogger errorLogger = new ErrorLogger(AbstractLogger.ERROR);        AbstractLogger debugLogger = new DebugLogger(AbstractLogger.DEBUG);        AbstractLogger infoLogger = new InfoLogger(AbstractLogger.INFO);        errorLogger.setNextLogger(debugLogger);        debugLogger.setNextLogger(infoLogger);        return errorLogger;    }    public static void main(String[] args) {        AbstractLogger loggerChain = getChainOfLoggers();        loggerChain.logMessage(AbstractLogger.INFO, "This is an information.");        System.out.println("=================");        loggerChain.logMessage(AbstractLogger.DEBUG, "This is a debug level information.");        System.out.println("=================");        loggerChain.logMessage(AbstractLogger.ERROR, "This is an error information.");    }}// outputInfo Console::Logger: This is an information.=================Debug Console::Logger: This is a debug level information.Info Console::Logger: This is a debug level information.=================Error Console::Logger: This is an error information.Debug Console::Logger: This is an error information.Info Console::Logger: This is an error information.