Mastering the Decorator Pattern in Spring Boot: A Multi‑Layered Example

Preface

This article introduces how to use the Decorator pattern, often called the Wrapper pattern, in a Spring Boot project through a practical example.

What Is the Decorator Pattern?

Official definition

The Decorator Pattern (also known as the Wrapper Pattern) adds functionality to an object without changing its original structure, offering a more flexible alternative to inheritance for extending object behavior. It belongs to the structural design patterns.

Plain language

It’s like composing: I don’t touch the original business logic, but I want to attach extra responsibilities to it.

Non‑intrusive.

Composable.

Practical Implementation

Scenario Overview

We define an interface ISurfTheInternetService representing an online‑surfing service, and two concrete implementations: FadInternetCafe (stylish internet cafe) and RetroInternetBar (retro internet bar).

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

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

@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;

@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 simple controller method invokes both services to demonstrate the basic behavior:

@Autowired
@Qualifier("fadInternetCafeService")
ISurfTheInternetService fadInternetCafeService;

@Autowired
@Qualifier("retroInternetBarService")
ISurfTheInternetService retroInternetBarService;

@GetMapping("/doTest")
public void doTest() {
    fadInternetCafeService.doSurfing();
    retroInternetBarService.doSurfing();
}

The console output shows each implementation’s message:

Adding a Decorator

We create SurfDecorator that implements the same interface and holds a reference to another ISurfTheInternetService. Its doSurfing method adds extra behavior before delegating to the wrapped service.

public class SurfDecorator implements ISurfTheInternetService {
    /** Internal reference to the original service */
    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,可能是一些额外的职责业务，比如说是XXXX");
    }
}

Controller usage:

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

    SurfDecorator retroInternetBarDecoratorService = new SurfDecorator(retroInternetBarService);
    retroInternetBarDecoratorService.doSurfing();
}

Multi‑Layer Decoration

Sometimes a single decorator is not enough. We create RechargeDecorator that extends SurfDecorator and adds a recharge‑checking step.

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");
    }
}

Controller method demonstrating two‑level decoration:

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

Through these examples we see how the Decorator pattern enables dynamic, non‑intrusive extension of business logic, and how multiple decorators can be stacked to compose complex behavior in a Spring Boot application.