Applying the Decorator Pattern in a Spring Boot Project: A Practical Guide

The article explains how to apply the Decorator pattern in a Spring Boot project to extend functionality without modifying existing classes.

Decorator (Wrapper) pattern is a structural design pattern that adds responsibilities to objects dynamically, offering a more flexible alternative to inheritance.

Example interface ISurfTheInternetService defines a doSurfing() method:

/**
 * @Author: JCccc
 * @Date: 2022-10-07 15:18
 * @Description: 网上冲浪
 */
public interface ISurfTheInternetService {
    /**
     * 冲起来
     */
    void doSurfing();
}

Two concrete implementations provide basic surfing behavior:

import com.example.mydemo.service.ISurfTheInternetService;
import org.springframework.stereotype.Service;

/**
 * @Author: JCccc
 * @Date: 2022-10-07 15:21
 * @Description: 时尚 网咖
 */
@Service("fadInternetCafeService")
public class FadInternetCafe implements ISurfTheInternetService {
    @Override
    public void doSurfing() {
        System.out.println("在时尚 网咖 ,网上冲浪咯~");
    }
}

import com.example.mydemo.service.ISurfTheInternetService;
import org.springframework.stereotype.Service;

/**
 * @Author: JCccc
 * @Date: 2022-10-07 15:21
 * @Description: 复古 网吧
 */
@Service("retroInternetBarService")
public class RetroInternetBar implements ISurfTheInternetService {
    @Override
    public void doSurfing() {
        System.out.println("在复古 网吧 ,网上冲浪咯~");
    }
}

A SurfDecorator class implements the same interface, holds a reference to an ISurfTheInternetService , and adds extra behavior before delegating:

/**
 * @Author: JCccc
 * @Date: 2022-10-07 15:29
 * @Description:
 */
public class SurfDecorator implements ISurfTheInternetService {
    private ISurfTheInternetService surfTheInternetService;
    public SurfDecorator(ISurfTheInternetService surfTheInternetService) {
        this.surfTheInternetService = surfTheInternetService;
    }
    @Override
    public void doSurfing() {
        System.out.println("SurfDecorator 模拟业务 增强器在玩一点很新的东西,可能是一些额外的职责业务....");
        surfTheInternetService.doSurfing();
        System.out.println("SurfDecorator 模拟业务 增强器在玩一点很新的东西,比如说是XXXX");
    }
}

Controller methods illustrate single‑layer decoration:

@GetMapping("/useDecoratorTest")
public void useDecoratorTest() {
    SurfDecorator fadInternetCafeDecoratorService = new SurfDecorator(fadInternetCafeService);
    fadInternetCafeDecoratorService.doSurfing();
    SurfDecorator retroInternetBarDecoratorService = new SurfDecorator(retroInternetBarService);
    retroInternetBarDecoratorService.doSurfing();
}

To demonstrate multi‑layer decoration, a RechargeDecorator extends SurfDecorator and adds a recharge‑checking step:

/**
 * @Author: JCccc
 * @Date: 2022-10-07 15:29
 * @Description:
 */
public class RechargeDecorator extends SurfDecorator {
    public RechargeDecorator(ISurfTheInternetService surfTheInternetService) {
        super(surfTheInternetService);
    }
    @Override
    public void doSurfing() {
        super.doSurfing();
        checkRecharge();
    }
    private void checkRecharge(){
        System.out.print("RechargeDecorator 也在增强,看看这个货卡里面充了有多少,就来上网");
    }
}

Multi‑layer usage in a controller:

@GetMapping("/moreDecoratorTest")
public void moreDecoratorTest() {
    // first layer
    SurfDecorator retroInternetBarDecoratorService = new SurfDecorator(retroInternetBarService);
    // second layer
    RechargeDecorator rechargeDecorator = new RechargeDecorator(retroInternetBarDecoratorService);
    rechargeDecorator.doSurfing();
}

Running the endpoints shows the original surfing messages together with the additional messages injected by the decorators, confirming that responsibilities can be stacked transparently.