设计模式系列:责任链模式

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概念

责任链模式顾名思义，它是由一连串单一职责的对象构成链式结构。此结构一般为请求接受者做前置业务处理，主要目的是
为发送者和接收者进行解耦。其特点是，每个对象都只处理自己成处理的请求，如果处理不了，会把请求传给下一个接收者。以此类推。

实现

一个简单的日志记录链

类图

图片

代码

AbstractLogger

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package com.littlehui.design.responsebilitychain;

/**
 * @Description TODO
 * @ClassName AbstractLogger
 * @Author littlehui
 * @Date 2019/7/29 15:12
 * @Version 1.0
 **/
public abstract class AbstractLogger {

    public static int INFO = 1;

    public static int WARN = 2;

    public static int ERROR = 3;

    protected int level;

    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);
}

ErrorLogger

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package com.littlehui.design.responsebilitychain;

/**
 * @Description TODO
 * @ClassName ErrorLogger
 * @Author littlehui
 * @Date 2019/7/29 15:15
 * @Version 1.0
 **/
public class ErrorLogger extends AbstractLogger {

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

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

InfoLogger

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package com.littlehui.design.responsebilitychain;

/**
 * @Description TODO
 * @ClassName InfoLogger
 * @Author littlehui
 * @Date 2019/7/29 15:16
 * @Version 1.0
 **/
public class InfoLogger extends AbstractLogger {

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

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

WarnLogger

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package com.littlehui.design.responsebilitychain;

/**
 * @Description TODO
 * @ClassName WarnLogger
 * @Author littlehui
 * @Date 2019/7/29 15:16
 * @Version 1.0
 **/
public class WarnLogger extends AbstractLogger {

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

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

Demo

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package com.littlehui.design.responsebilitychain;

/**
 * @Description TODO
 * @ClassName Demo
 * @Author littlehui
 * @Date 2019/7/29 15:18
 * @Version 1.0
 **/
public class Demo {

    private static AbstractLogger getChainOfLoggers(){

        AbstractLogger errorLogger = new ErrorLogger(AbstractLogger.ERROR);
        AbstractLogger infoLogger = new InfoLogger(AbstractLogger.INFO);
        AbstractLogger warnLogger = new WarnLogger(AbstractLogger.WARN);

        errorLogger.setNextLogger(infoLogger);
        infoLogger.setNextLogger(warnLogger);
        return errorLogger;
    }

    public static void main(String[] args) {
        AbstractLogger loggerChain = getChainOfLoggers();
        loggerChain.logMessage(AbstractLogger.INFO, "This is an information.");
        loggerChain.logMessage(AbstractLogger.WARN,
                "This is a warn level information.");
        loggerChain.logMessage(AbstractLogger.ERROR,
                "This is an error information.");
    }
}

执行结果：

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/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/bin/java -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:65034,suspend=y,server=n -Dfile.encoding=UTF-8 -classpath "/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/tools.jar:/Users/littlehui/WorkSpaces/Home/pattern/out/production/responsbilitychain:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar" com.littlehui.design.responsebilitychain.Demo
Connected to the target VM, address: '127.0.0.1:65034', transport: 'socket'
Error Console::Logger: This is an information.
Error Console::Logger: This is a warn level information.
Error Console::Logger: This is a warn level information.
Error Console::Logger: This is an error information.
Error Console::Logger: This is an error information.
Error Console::Logger: This is an error information.
Disconnected from the target VM, address: '127.0.0.1:65034', transport: 'socket'

Process finished with exit code 0

场景

  • Spring MVC的filter，Interceptor各种Handler等等
  • 日志记录

总结

责任链的特点是单一职责，链式结构。前提是统一的输入端。
在遇到复杂业务，特别是复杂请求时候。输入端是统一的，这时候就可以考虑将业务处理拆分成单一的
职责。再将对象链接起来。这样的好处是，解耦了接收端的处理。并且提升了扩展性能。维护也方便。