stream優化責任鏈設計模式 responsibility chains

責任鏈設計模式傳統的實現方式：

public class TestMaxBy {

    public static void main(String[] args) {
        CookieStep1 step1 = new CookieStep1();
        step1.setSuccessor(new CookieStep2());
        Cookie cookie = step1.handle(new Cookie());
        System.out.println(cookie);
    }
}

abstract class ProcessStep<T>{

    private ProcessStep<T> successor;

    public void setSuccessor(ProcessStep<T> s){
        this.successor = s;
    }

    public T handle(T t){
        T t2 = dealWith(t);
        if(successor != null){
            return successor.handle(t2);
        }
        return t2;
    }

    abstract T dealWith(T t);
}

class CookieStep1 extends ProcessStep<Cookie>{

    @Override
    Cookie dealWith(Cookie cookie) {
        cookie.setFlavor("Blue berry");
        return cookie;
    }
}

class CookieStep2 extends ProcessStep<Cookie>{

    @Override
    Cookie dealWith(Cookie cookie) {
        cookie.setWrapper("Dedicated plastic bag");
        return cookie;
    }
}

class Cookie{
    private String wrapper;

    private String flavor;

    public void setWrapper(String wrapper) {
        this.wrapper = wrapper;
    }

    public void setFlavor(String flavor) {
        this.flavor = flavor;
    }

    public String toString(){
        return flavor + " in a " + wrapper;
    }
}

用lambda簡化後的責任鏈模式：

import java.util.function.Function;
import java.util.function.UnaryOperator;

public class ResponsibilityChain {

    public static void main(String[] args) {
        UnaryOperator<Cookie> operator1 = (cookie) -> {cookie.setFlavor("milk"); return cookie;};
        UnaryOperator<Cookie> operator2 = (cookie) -> {cookie.setWrapper("dedicated plastic bag"); return cookie;};
        Function<Cookie, Cookie> func = operator1.andThen(operator2);
        Cookie cookie = func.apply(new Cookie());
        System.out.println(cookie);
    }
}

class Cookie{
    private String wrapper;

    private String flavor;

    public void setWrapper(String wrapper) {
        this.wrapper = wrapper;
    }

    public void setFlavor(String flavor) {
        this.flavor = flavor;
    }

    public String toString(){
        return flavor + " in a " + wrapper;
    }
}