責(zé)任鏈模式

• 責(zé)任鏈模式（Chain of Responsibility Pattern）
• 責(zé)任鏈模式將鏈中每一個(gè)節(jié)點(diǎn)都看作一個(gè)對(duì)象谭跨，每個(gè)節(jié)點(diǎn)處理的請(qǐng)求均不同孕暇，且內(nèi)部自動(dòng)維護(hù)下一個(gè)節(jié)點(diǎn)對(duì)象澈侠。
• 當(dāng)一個(gè)請(qǐng)求從鏈?zhǔn)降氖锥税l(fā)出時(shí)菩鲜，會(huì)沿著責(zé)任鏈預(yù)設(shè)的路徑依次傳遞到每一個(gè)節(jié)點(diǎn)對(duì)象罩引，直至被鏈中的某個(gè)對(duì)象處理為止

優(yōu)點(diǎn)：職責(zé)鏈模式使多個(gè)對(duì)象都有機(jī)會(huì)處理請(qǐng)求嘹悼，從而避免請(qǐng)求的發(fā)送者和接收者之間的耦合關(guān)系

1.2 兩個(gè)角色

（1）抽象處理者（Handler）：定義處理請(qǐng)求的方法嵌器，并維護(hù)一個(gè)下一處理節(jié)點(diǎn)Handler對(duì)象的引用
（2）具體處理者（ConcreteHandler）：對(duì)請(qǐng)求進(jìn)行處理肛真，如果不感興趣，則進(jìn)行轉(zhuǎn)發(fā)

2. 示例

用戶的請(qǐng)求傳遞爽航，直到可以解決這個(gè)請(qǐng)求為止

image.png

public abstract class AbstractHandler {

    protected AbstractHandler successor;
    /**
     * 設(shè)置繼任者
     */
    public void setSuccessor(AbstractHandler successor) {
        this.successor = successor;
    }

    protected abstract void doHandle(String request);
}

public class ConcreteHandlerA extends AbstractHandler {
    @Override
    protected void doHandle(String request) {
        if (request.startsWith("handlerA")) {
            System.out.println("ConcreteHandlerA execute: " + request);
        } else {
            // 請(qǐng)求向下傳遞
            successor.doHandle(request);
        }
    }
}

public class ConcreteHandlerB extends AbstractHandler {
    @Override
    public void doHandle(String request) {
        if (request.startsWith("handlerB")) {
            System.out.println("ConcreteHandlerB execute: " + request);
        } else {
            successor.doHandle(request);
        }
    }
}

public class ConcreteHandlerC extends AbstractHandler {
    @Override
    protected void doHandle(String request) {
        if (request.startsWith("handlerC")) {
            System.out.println("ConcreteHandlerC execute: " + request);
        } else {
            successor.doHandle(request);
        }
    }
}

測(cè)試：

@Test
public void test() {
    AbstractHandler handlerA = new ConcreteHandlerA();
    AbstractHandler handlerB = new ConcreteHandlerB();
    AbstractHandler handlerC = new ConcreteHandlerC();
    handlerA.setSuccessor(handlerB);
    handlerB.setSuccessor(handlerC);

    List<String> list = Arrays.asList("handlerA000", "handlerB111", "handlerC222");
    for (String str : list) {
        handlerA.doHandle(str);
    }
}
``
## 3. 其他
```java
public abstract class AbstractHandle {

    public static void main(String[] args) {
        AbstractHandle handle = Builder.create()
                .addHandler(new ValidateHandle())
                .addHandler(new LoginHandle())
                .addHandler(new AuthHandle())
                .build();
        handle.doHandle("111");
    }

    protected AbstractHandle chain;

    public void next(AbstractHandle handle) {
        this.chain = handle;
    }

    /**
     * 抽象方法
     * @param request
     */
    public abstract void doHandle(String request);

    public static class Builder {
        private AbstractHandle head;
        private AbstractHandle tail;

        public Builder addHandler(AbstractHandle handle) {
            if (this.head == null) {
                this.head = this.tail = handle;
                return this;
            }
            this.tail.next(handle);
            this.tail = handle;
            return this;
        }

        public AbstractHandle build() {
            return this.head;
        }

        public static Builder create() {
            return new Builder();
        }
    }
}

class ValidateHandle extends AbstractHandle {
    @Override
    public void doHandle(String request) {
        System.out.println("ValidateHandle start");
        if (chain != null) {
            chain.doHandle(request);
        }
    }
}

class LoginHandle extends AbstractHandle {
    @Override
    public void doHandle(String request) {
        System.out.println("LoginHandle start");
        if (chain != null) {
            chain.doHandle(request);
        }
    }
}

class AuthHandle extends AbstractHandle {
    @Override
    public void doHandle(String request) {
        System.out.println("AuthHandle start");
        // 若還有下一級(jí)蚓让，請(qǐng)求繼續(xù)傳遞
        if (chain != null) {
            chain.doHandle(request);
        }
    }
}