Responsibility chain model of behavioral model

The chain of responsibility model

What is it? ？

Responsibility chain （Chain of Responsibility） Pattern ： In order to avoid coupling the request sender with multiple request processors , Thus, all the request processors are connected in a chain by remembering the reference of the next object by the previous object ; When a request occurs , The request can be passed along this chain , Until an object processes it . There are similar examples in life , For example, purchase approval process 、 Leave process, etc ; It is also very common in computer software and hardware , Like interceptors , filter , Can consider the responsibility chain model to achieve .
In the responsibility chain model , The customer just needs to send the request to the chain of responsibility , Don't care about the processing details of the request and the delivery process of the request , The request is automatically delivered . So the chain of responsibility decouples the sender of the request from the handler of the request .

advantage

1. It reduces the coupling between objects . This pattern makes it unnecessary for an object to know which object handles its request and the structure of the chain , Neither the sender nor the receiver has to have the other party's explicit information .
2. Enhanced system scalability . You can add new request processing classes as needed , It satisfies the open close principle .‘
3. Increased flexibility in assigning responsibilities to objects . When the workflow changes , Can dynamically change the members of the chain or transfer their order , You can also dynamically add or delete responsibilities .
4. The chain of responsibility simplifies the connection between objects . Each object only needs to keep a reference to its successors , No need to keep references from all other processors .
5. Share responsibility . Each class only needs to handle its own work , What should not be processed is passed to the next object to complete , Clarify the scope of responsibility of all kinds , According to the single responsibility principle of class .

shortcoming

1. There is no guarantee that every request will be processed . Because a request has no clear recipient , So there's no guarantee that it will be dealt with , The request may not be processed all the way to the end of the chain .
2. For a longer responsibility chain , The processing of the request may involve multiple processing objects , System performance will be affected ,
3. The rationality of responsibility chain establishment depends on the client to ensure , Increased client complexity , System error may be caused by wrong setting of responsibility chain , If it is possible to cause a circular call .

The structure of the pattern

Realization

Use the leave approval module to simply simulate the application of the responsibility chain mode .
scene ： Students ask for leave

Students ask for leave less than 2 God , The head teacher can directly approve ; Students ask for leave less than 7 God , The dean of the Department can directly approve ; Less than 10 God , The president can approve , The rest will not be approved .

Code implementation

Headmaster , The dean of the Department , dean

package com.pattern.chainOfResponsibility;

/** * @author wlj * @Classname Leader * @Description  Abstract leadership  * @Date 7/24/2022 10:35 PM */
public abstract class Leader {
    
    //  The next citation of responsibility 
    private Leader next;

    public Leader getNext() {
    
        return next;
    }

    public void setNext(Leader next) {
    
        this.next = next;
    }

    /** *  Deal with students' leave requests  * @param day  The number of days students ask for leave  */
    public abstract void handleRequest(int day);
}
//  Headmaster 
package com.pattern.chainOfResponsibility;

/** * @author wlj * @Classname ClassAdviser * @Description  Headmaster  * @Date 7/24/2022 10:42 PM */
public class ClassAdviser extends Leader{
    
    @Override
    public void handleRequest(int day) {
    
        if(day <= 2){
    
             System.out.println(" Approved by the head teacher :"+day);
        }else{
    
            if(getNext() != null){
    
                getNext().handleRequest(day);
            }
            else{
    
                System.out.println(" Too many days off , Not approved ");
            }
        }
    }
}
//  The dean of the Department 
package com.pattern.chainOfResponsibility;

/** * @author wlj * @Classname ClassAdviser * @Description  The dean of the Department  * @Date 7/24/2022 10:42 PM */
public class DepartmentHead extends Leader{
    
    @Override
    public void handleRequest(int day) {
    
        if(day <= 7){
    
            System.out.println(" Approved by the Dean :"+day);
        }else{
    
            if(getNext() != null){
    
                getNext().handleRequest(day);
            }
            else{
    
                System.out.println(" Too many days off , Not approved ");
            }
        }
    }
}
//  dean 
package com.pattern.chainOfResponsibility;

/** * @author wlj * @Classname ClassAdviser * @Description  dean  * @Date 7/24/2022 10:42 PM */
public class Dean extends Leader{
    
    @Override
    public void handleRequest(int day) {
    
        if(day <= 10){
    
             System.out.println(" Approved by the president :"+day);
        }else{
    
            if(getNext() != null){
    
                getNext().handleRequest(day);
            }
            else{
    
                System.out.println(" Too many days off , Not approved ");
            }
        }
    }
}

client

package com.pattern.chainOfResponsibility;

/** * @author wlj * @Classname Client * @Description  Scene simulation  * @Date 7/24/2022 10:51 PM */
public class Client {
    
    public static void main(String[] args) {
    
        //  Build a chain of responsibility 
        Leader leader1 = new ClassAdviser();
        Leader leader2 = new DepartmentHead();
        Leader leader3 = new Dean();
        // leader1(ClassAdviser) -> leader2(DepartmentHead) ->leader3(Dean)
        leader1.setNext(leader2);
        leader2.setNext(leader3);
        leader3.setNext(null);
        //  Simulated leave 2 God 
        leader1.handleRequest(2);
        //  Simulated leave 8 God 
        leader1.handleRequest(7);
        //  Simulated leave 9 God 
        leader1.handleRequest(9);
        //  Simulated leave 12 God 
        leader1.handleRequest(12);
    }
}

output:
 Approved by the head teacher :2
 Approved by the Dean :7
 Approved by the president :9
 Too many days off , Not approved