Chain Of Responsibility

责任链

---

定义

使多个对象都有机会处理请求，从而避免请求的发送者和接收者之间的耦合关系。将这些对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。

多个处理器按照一定顺序组合排列，依次处理请求

栗子

财务申报

package eternal.fire;

import java.math.BigDecimal;

public class Main {
    public static void main(String[] args) {
        HandlerChain handlerChain = new HandlerChain();
        handlerChain.addHandler(new ManagerHandler());
        handlerChain.addHandler(new DirectorHandler());
        handlerChain.addHandler(new CEOHandler());
        handlerChain.process(new Request("Doomfist", new BigDecimal(123123)));
        handlerChain.process(new Request("tracer", new BigDecimal(1231231)));
    }
}
package eternal.fire;

import java.util.LinkedList;
import java.util.List;

public class HandlerChain {
    List<Handler> handlerList = new LinkedList<>();

    public void addHandler(Handler handler) {
        this.handlerList.add(handler);
    }
    
    public boolean process(Request request) {
        for (var handler : handlerList) {
            Boolean result = handler.process(request);
            if (result != null) {
                if (result) {
                    System.out.println(request + " Approved by " + handler.getClass().getSimpleName());
                } else {
                    System.out.println(request + " Denied by " + handler.getClass().getSimpleName());
                }
                return result;
            }
        }
        throw new RuntimeException("idk");
    }

}
package eternal.fire;

import java.math.BigDecimal;

public class Request {
    private String name;
    private BigDecimal amount;

    public Request(String name, BigDecimal amount) {
        this.name = name;
        this.amount = amount;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public BigDecimal getAmount() {
        return amount;
    }
    
    public void setAmount(BigDecimal amount) {
        this.amount = amount;
    }
    
    @Override
    public String toString() {
        return "Request:" + this.name + "," + this.amount;
    }

}
package eternal.fire;

public interface Handler {
    /**
     *
     * @param request the request which are waiting to be handled
     * @return true if success, false if refuse, null if pass to next handler
     */
    Boolean process(Request request);
}
package eternal.fire;

import java.math.BigDecimal;

public class ManagerHandler implements Handler{
    @Override
    public Boolean process(Request request) {
        return request.getAmount().compareTo(BigDecimal.valueOf(1000)) > 0 ? null : !request.getName().equals("Doomfist");//英雄歧视搞起来
    }
}

Filter

实现

处理器接口

• 实现类

组合各种处理器