10.20

責任鏈模式

責任鏈模式（Chain of Responsibility Pattern）是一種行為型設計模式，它將請求的傳送者和接收者解耦，使多個物件都有機會處理這個請求。每個接收者都包含對下一個接收者的引用，形成一個鏈條，請求沿著這個鏈條依次傳遞，直到有一個接收者處理它。

下面是一個簡單的Java程式碼示例，演示了責任鏈模式的實現：

// 請求類
class Request {
    private String content;

    public Request(String content) {
        this.content = content;
    }

    public String getContent() {
        return content;
    }
}

// 處理者介面
interface Handler {
    void setNext(Handler nextHandler);
    void handleRequest(Request request);
}

// 具體處理者A
class ConcreteHandlerA implements Handler {
    private Handler nextHandler;

    public void setNext(Handler nextHandler) {
        this.nextHandler = nextHandler;
    }

    public void handleRequest(Request request) {
        if (request.getContent().equals("A")) {
            System.out.println("ConcreteHandlerA handles the request.");
        } else if (nextHandler != null) {
            nextHandler.handleRequest(request);
        }
    }
}

// 具體處理者B
class ConcreteHandlerB implements Handler {
    private Handler nextHandler;

    public void setNext(Handler nextHandler) {
        this.nextHandler = nextHandler;
    }

    public void handleRequest(Request request) {
        if (request.getContent().equals("B")) {
            System.out.println("ConcreteHandlerB handles the request.");
        } else if (nextHandler != null) {
            nextHandler.handleRequest(request);
        }
    }
}

// 客戶端程式碼
public class ChainOfResponsibilityPatternExample {
    public static void main(String[] args) {
        Handler handlerA = new ConcreteHandlerA();
        Handler handlerB = new ConcreteHandlerB();

        handlerA.setNext(handlerB);

        Request request1 = new Request("A");
        handlerA.handleRequest(request1);

        Request request2 = new Request("B");
        handlerA.handleRequest(request2);

        Request request3 = new Request("C");
        handlerA.handleRequest(request3);
    }
}