【设计模式】用Java实现职责链模式

// 抽象处理者
abstract class Handler {
    private Handler nextHandler;
    public void setNextHandler(Handler nextHandler) {
        this.nextHandler = nextHandler;
    }
    public void handleRequest(Request request) {
        if (canHandle(request)) {
            processRequest(request);
        } else if (nextHandler != null) {
            nextHandler.handleRequest(request);
        } else {
            System.out.println("No handler found for the request.");
        }
    }
    protected abstract boolean canHandle(Request request);
    protected abstract void processRequest(Request request);
}
// 具体处理者 - 文件处理器
class FileHandler extends Handler {
    protected boolean canHandle(Request request) {
        return request.getType().equals("file");
    }
    protected void processRequest(Request request) {
        System.out.println("FileHandler is processing the request: " + request.getData());
    }
}
// 具体处理者 - 数据库处理器
class DatabaseHandler extends Handler {
    protected boolean canHandle(Request request) {
        return request.getType().equals("database");
    }
    protected void processRequest(Request request) {
        System.out.println("DatabaseHandler is processing the request: " + request.getData());
    }
}
// 具体处理者 - API处理器
class ApiHandler extends Handler {
    protected boolean canHandle(Request request) {
        return request.getType().equals("api");
    }
    protected void processRequest(Request request) {
        System.out.println("ApiHandler is processing the request: " + request.getData());
    }
}
// 请求类
class Request {
    private String type;
    private String data;
    public Request(String type, String data) {
        this.type = type;
        this.data = data;
    }
    public String getType() {
        return type;
    }
    public String getData() {
        return data;
    }
}
// 使用示例
public class Main {
    public static void main(String[] args) {
        Handler fileHandler = new FileHandler();
        Handler databaseHandler = new DatabaseHandler();
        Handler apiHandler = new ApiHandler();
        fileHandler.setNextHandler(databaseHandler);
        databaseHandler.setNextHandler(apiHandler);
        Request fileRequest = new Request("file", "SampleFile.txt");
        Request databaseRequest = new Request("database", "SELECT * FROM Users");
        Request apiRequest = new Request("api", "POST /api/users");
        fileHandler.handleRequest(fileRequest);
        fileHandler.handleRequest(databaseRequest);
        fileHandler.handleRequest(apiRequest);
    }
}

// 请求类
class PurchaseRequest {
    private String product;
    private double price;
    public PurchaseRequest(String product, double price) {
        this.product = product;
        this.price = price;
    }
    public String getProduct() {
        return product;
    }
    public double getPrice() {
        return price;
    }
}
// 抽象处理者
abstract class Approver {
    protected Approver successor;
    public void setSuccessor(Approver successor) {
        this.successor = successor;
    }
    public abstract void processRequest(PurchaseRequest request);
}
// 具体处理者 - 销售经理
class SalesManager extends Approver {
    public void processRequest(PurchaseRequest request) {
        if (request.getPrice() <= 1000) {
            System.out.println("Sales Manager approves the purchase of " + request.getProduct());
        } else if (successor != null) {
            successor.processRequest(request);
        }
    }
}
// 具体处理者 - 财务经理
class FinanceManager extends Approver {
    public void processRequest(PurchaseRequest request) {
        if (request.getPrice() <= 5000) {
            System.out.println("Finance Manager approves the purchase of " + request.getProduct());
        } else if (successor != null) {
            successor.processRequest(request);
        }
    }
}
// 具体处理者 - CEO
class CEO extends Approver {
    public void processRequest(PurchaseRequest request) {
        if (request.getPrice() <= 10000) {
            System.out.println("CEO approves the purchase of " + request.getProduct());
        } else {
            System.out.println("Purchase request for " + request.getProduct() + " denied by CEO");
        }
    }
}
// 使用示例
public class Main {
    public static void main(String[] args) {
        Approver salesManager = new SalesManager();
        Approver financeManager = new FinanceManager();
        Approver ceo = new CEO();
        salesManager.setSuccessor(financeManager);
        financeManager.setSuccessor(ceo);
        PurchaseRequest request1 = new PurchaseRequest("Laptop", 800);
        PurchaseRequest request2 = new PurchaseRequest("Smartphone", 3000);
        PurchaseRequest request3 = new PurchaseRequest("Conference Table", 12000);
        salesManager.processRequest(request1);
        salesManager.processRequest(request2);
        salesManager.processRequest(request3);
    }
}