How to specify the execution order in a Java chain of responsibility pattern?

1 year ago
Jackson Davis
2 minutes

In the Java Chain of Responsibility pattern, the execution order can be specified using the following method:

  1. Define an abstract base class or interface for the responsibility chain, which includes a method for handling and another method for setting the next handler.
  2. The handling method is implemented in the specific handler class, and the responsibility chain is connected by setting the next handler method.
  3. Create specific handler objects in the client code and establish the next handler in a specified order.
  4. Invoke the handling method of the chain of responsibility, passing the request to the first handler.
  5. After each handler finishes processing the request, they can choose to pass the request to the next handler, or simply end the processing.

Here is a simple example code:

// 定义责任链的抽象基类
public abstract class Handler {
    protected Handler nextHandler;

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

    public abstract void handleRequest(String request);
}

// 具体的处理者类
public class ConcreteHandler1 extends Handler {
    public void handleRequest(String request) {
        if (request.equals("A")) {
            System.out.println("ConcreteHandler1处理了请求：" + request);
        } else if (nextHandler != null) {
            nextHandler.handleRequest(request);
        }
    }
}

public class ConcreteHandler2 extends Handler {
    public void handleRequest(String request) {
        if (request.equals("B")) {
            System.out.println("ConcreteHandler2处理了请求：" + request);
        } else if (nextHandler != null) {
            nextHandler.handleRequest(request);
        }
    }
}

// 客户端代码
public class Client {
    public static void main(String[] args) {
        // 创建具体的处理者对象
        Handler handler1 = new ConcreteHandler1();
        Handler handler2 = new ConcreteHandler2();

        // 按照指定的顺序设置下一个处理者
        handler1.setNextHandler(handler2);

        // 调用责任链的处理方法
        handler1.handleRequest("A");
        handler1.handleRequest("B");
    }
}

In the above example, two specific handler objects are first created, then they are connected by setting the next handler method. Finally, the handle method of the chain is called to pass the request to the first handler. During the handling process, if a handler is able to process the request, it will do so and end; otherwise, the request is passed on to the next handler. This way, the handlers in the chain can be executed in the specified order.

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