Design Pattern - Chain of Responsibility（Java）

2023-08-18 20:54:40

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Definition

Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.

Participants

The classes and/or objects participating in this pattern are:

Handler (Approver)
- Defines an interface for handling the requests
- (optional) Implements the successor link
ConcreteHandler (Director, VicePresident, President)
- Handles requests it is responsible for
- Can access its successor
- If the ConcreteHandler can handle the request, it does so; otherwise it forwards the request to its successor
Client (ChainApp)
- Initiates the request to a ConcreteHandler object on the chain

Sample Code in Java

This structural code demonstrates the Chain of Responsibility pattern in which several linked objects (the Chain) are offered the opportunity to respond to a request or hand it off to the object next in line.

/*
 *  Chimomo's Blog: https://blog.csdn.net/chimomo/
 */
package chimomo.learning.java.designpattern.chainofresponsibility.sample;

/**
 * The 'ConcreteHandler1' class.
 *
 * @author Chimomo
 */
class ConcreteHandler1 extends Handler {

    /**
     * Handle request.
     *
     * @param request
     */
    @Override
    public void handleRequest(int request) {
        if (request >= 0 && request < 10) {
            System.out.println(String.format("%s handled request %d", this.getClass().getSimpleName(), request));
        } else if (this.successor != null) {
            this.successor.handleRequest(request);
        }
    }

}

/*
 *  Chimomo's Blog: https://blog.csdn.net/chimomo/
 */
package chimomo.learning.java.designpattern.chainofresponsibility.sample;

/**
 * The 'ConcreteHandler2' class.
 *
 * @author Chimomo
 */
class ConcreteHandler2 extends Handler {

    /**
     * Handle request.
     *
     * @param request
     */
    @Override
    public void handleRequest(int request) {
        if (request >= 10 && request < 20) {
            System.out.println(String.format("%s handled request %d", this.getClass().getSimpleName(), request));
        } else if (this.successor != null) {
            this.successor.handleRequest(request);
        }
    }

}

/*
 *  Chimomo's Blog: https://blog.csdn.net/chimomo/
 */
package chimomo.learning.java.designpattern.chainofresponsibility.sample;

/**
 * The 'ConcreteHandler3' class.
 *
 * @author Chimomo
 */
class ConcreteHandler3 extends Handler {

    /**
     * Handle request.
     *
     * @param request
     */
    @Override
    public void handleRequest(int request) {
        if (request >= 20 && request < 30) {
            System.out.println(String.format("%s handled request %d", this.getClass().getSimpleName(), request));
        } else if (this.successor != null) {
            this.successor.handleRequest(request);
        }
    }

}

/*
 *  Chimomo's Blog: https://blog.csdn.net/chimomo/
 */
package chimomo.learning.java.designpattern.chainofresponsibility.sample;

/**
 * The 'Handler' abstract class.
 *
 * @author Chimomo
 */
abstract class Handler {

    // The successor.
    protected Handler successor;

    /**
     * Handle request.
     *
     * @param request
     */
    public abstract void handleRequest(int request);

    /**
     * Set successor.
     *
     * @param successor
     */
    public void setSuccessor(Handler successor) {
        this.successor = successor;
    }

}

/*
 *  Chimomo's Blog: https://blog.csdn.net/chimomo/
 */
package chimomo.learning.java.designpattern.chainofresponsibility.sample;

/**
 * Startup class for Structural Chain of Responsibility Design Pattern.
 *
 * @author Chimomo
 */
class Program {

    /**
     * Entry point into console application.
     *
     * @param args The arguments
     */
    public static void main(String[] args) {

        // Setup Chain of Responsibility.
        Handler h1 = new ConcreteHandler1();
        Handler h2 = new ConcreteHandler2();
        Handler h3 = new ConcreteHandler3();
        h1.setSuccessor(h2);
        h2.setSuccessor(h3);

        // Generate and process request.
        int[] requests = {2, 5, 14, 22, 18, 3, 27, 20};
        for (int request : requests) {
            h1.handleRequest(request);
        }
    }

}

/*
Output:
ConcreteHandler1 handled request 2
ConcreteHandler1 handled request 5
ConcreteHandler2 handled request 14
ConcreteHandler3 handled request 22
ConcreteHandler2 handled request 18
ConcreteHandler1 handled request 3
ConcreteHandler3 handled request 27
ConcreteHandler3 handled request 20
 */

This real-world code demonstrates the Chain of Responsibility pattern in which several linked managers and executives can respond to a purchase request or hand it off to a superior. Each position has can its own set of rules which orders they can approve.

/*
 *  Chimomo's Blog: https://blog.csdn.net/chimomo/
 */
package chimomo.learning.java.designpattern.chainofresponsibility.realworld;

/**
 * The 'Handler' abstract class.
 *
 * @author Chimomo
 */
abstract class Approver {

    // The successor.
    protected Approver successor;

    /**
     * Process request.
     *
     * @param purchase
     */
    public abstract void processRequest(Purchase purchase);

    /**
     * Set successor.
     *
     * @param successor
     */
    public void setSuccessor(Approver successor) {
        this.successor = successor;
    }

}

/*
 *  Chimomo's Blog: https://blog.csdn.net/chimomo/
 */
package chimomo.learning.java.designpattern.chainofresponsibility.realworld;

/**
 * The 'ConcreteHandler' class.
 *
 * @author Chimomo
 */
class Director extends Approver {

    /**
     * Process request.
     *
     * @param purchase
     */
    @Override
    public void processRequest(Purchase purchase) {
        if (purchase.getAmount() < 10000.0) {
            System.out.println(String.format("%s approved request #%d", this.getClass().getSimpleName(), purchase.getNumber()));
        } else if (this.successor != null) {
            this.successor.processRequest(purchase);
        }
    }

}

/*
 *  Chimomo's Blog: https://blog.csdn.net/chimomo/
 */
package chimomo.learning.java.designpattern.chainofresponsibility.realworld;

/**
 * The 'ConcreteHandler' class.
 *
 * @author Chimomo
 */
class President extends Approver {

    /**
     * Process request.
     *
     * @param purchase
     */
    @Override
    public void processRequest(Purchase purchase) {
        if (purchase.getAmount() < 100000.0) {
            System.out.println(String.format("%s approved request #%d", this.getClass().getSimpleName(), purchase.getNumber()));
        } else {
            System.out.println(String.format("Request #%d requires an executive meeting!", purchase.getNumber()));
        }
    }

}

/*
 *  Chimomo's Blog: https://blog.csdn.net/chimomo/
 */
package chimomo.learning.java.designpattern.chainofresponsibility.realworld;

/**
 * Startup class for Real-World Chain of Responsibility Design Pattern.
 *
 * @author Chimomo
 */
class Program {

    /**
     * Entry point into console application.
     *
     * @param args The arguments
     */
    public static void main(String[] args) {

        // Setup Chain of Responsibility.
        Approver larry = new Director();
        Approver sam = new VicePresident();
        Approver tammy = new President();
        larry.setSuccessor(sam);
        sam.setSuccessor(tammy);

        // Generate and process purchase requests.
        Purchase p = new Purchase(2034, 350.00, "Assets");
        larry.processRequest(p);
        p = new Purchase(2035, 32590.10, "Project X");
        larry.processRequest(p);
        p = new Purchase(2036, 122100.00, "Project Y");
        larry.processRequest(p);
    }

}

/*
Output:
Director approved request #2034
President approved request #2035
Request #2036 requires an executive meeting!
 */

/*
 *  Chimomo's Blog: https://blog.csdn.net/chimomo/
 */
package chimomo.learning.java.designpattern.chainofresponsibility.realworld;

/**
 * Class holding request details.
 *
 * @author Chimomo
 */
class Purchase {

    // The amount.
    private double amount;

    // The number.
    private int number;

    // The purpose.
    private String purpose;

    /**
     * Initializes a new instance of the "Purchase" class.
     *
     * @param number
     * @param amount
     * @param purpose
     */
    public Purchase(int number, double amount, String purpose) {
        this.number = number;
        this.amount = amount;
        this.purpose = purpose;
    }

    /**
     * Get amount.
     *
     * @return
     */
    public double getAmount() {
        return this.amount;
    }

    /**
     * Get number.
     *
     * @return
     */
    public int getNumber() {
        return this.number;
    }

    /**
     * Get purpose.
     *
     * @return
     */
    public String getPurpose() {
        return this.purpose;
    }

}

/*
 *  Chimomo's Blog: https://blog.csdn.net/chimomo/
 */
package chimomo.learning.java.designpattern.chainofresponsibility.realworld;

/**
 * The 'ConcreteHandler' class.
 *
 * @author Chimomo
 */
class VicePresident extends Approver {

    /**
     * Process request.
     *
     * @param purchase
     */
    @Override
    public void processRequest(Purchase purchase) {
        if (purchase.getAmount() < 25000.0) {
            System.out.println(String.format("%s approved request #%d", this.getClass().getSimpleName(), purchase.getNumber()));
        } else if (this.successor != null) {
            this.successor.processRequest(purchase);
        }
    }

}

码农公寓

Definition

Participants

Sample Code in Java

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