责任链模式

╰+哭是因爲堅強的太久メ 2022-05-30 07:57 41阅读 0赞

责任链模式目的是为了避免请求发送者与请求接收者耦合，从而给予多个对象来处理同一个请求，链收到请求之后，会沿着链传递请求，直至有对象处理它。现实中的例子：

*  银行业务场景中，你的请求可能在多个部门当中依次传递，直至特定部门进行处理。
 *  ATM机使用责任链模式进行用户取钱吐钞  
    ![这里写图片描述][70]  
    ![这里写图片描述][70 1]

### 代码示例 ###

> 责任链上的Handler接口

public interface EmailHandler {
    
        void setNext(EmailHandler handler);
    
        void handleRequest(Email email);
    }

> 具体处理者

public class PersonalMailHandler implements EmailHandler { 
        private EmailHandler next;
    
        public void setNext(EmailHandler handler) {
            next = handler;
        }
    
        public void handleRequest(Email email) {
            if (!email.getFrom().endsWith("@gmail.com")) {
                next.handleRequest(email);
            } else {
                //handle request (move to correct folder)
                System.out.println("move to gmail folder");
            }
        }
    }

public class BusinessMailHandler implements EmailHandler { 
        private EmailHandler next;
    
        public void setNext(EmailHandler handler) {
            next = handler;
        }
    
        public void handleRequest(Email email) {
            if (!email.getFrom().endsWith("@businessaddress.com")) {
                next.handleRequest(email);
            } else {
                //handle request (move to correct folder)
                System.out.println("move to work folder");
            }
        }
    }

> 责任链

public class EmailProcessor {
        //maintain a reference to the previous handler so we can add the next one
        private EmailHandler prevHandler;
    
        public void addHandler(EmailHandler handler) {
            if (prevHandler != null) {
                prevHandler.setNext(handler);
            } else {
                prevHandler = handler;
            }
        }
    
        public void handleRequest(Email email) {
            prevHandler.handleRequest(email);
        }
    }

> 处理请求

public class EmailClient {
        private EmailProcessor processor;
    
        public EmailClient() {
            createProcessor();
        }
    
        private void createProcessor() {
            processor = new EmailProcessor();
            processor.addHandler(new BusinessMailHandler());
            processor.addHandler(new PersonalMailHandler());
        }
    
        public void addRule(EmailHandler handler) {
            processor.addHandler(handler);
        }
    
        public void emailReceived(Email email) {
            processor.handleRequest(email);
        }
    
        public static void main(String[] args) {
            EmailClient client = new EmailClient();
            Email email0 = new Email("test@gmail.com");
            Email email1 = new Email("test@businessaddress.com");
            client.emailReceived(email0);
            client.emailReceived(email1);
    
        }
    }

[https://dzone.com/articles/design-patterns-uncovered-chain-of-responsibility][https_dzone.com_articles_design-patterns-uncovered-chain-of-responsibility]

[https://sourcemaking.com/design\_patterns/chain\_of\_responsibility][https_sourcemaking.com_design_patterns_chain_of_responsibility]

[70]: /images/20220530/d706b2b3718940e8a6d30775db15c123.png
[70 1]: /images/20220530/2d0658075507452582d568436897004a.png
[https_dzone.com_articles_design-patterns-uncovered-chain-of-responsibility]: https://dzone.com/articles/design-patterns-uncovered-chain-of-responsibility
[https_sourcemaking.com_design_patterns_chain_of_responsibility]: https://sourcemaking.com/design_patterns/chain_of_responsibility