Spring proxies can be a bit of a mystery, right? When I first started working with Spring AOP (Aspect-Oriented Programming), I kept running into two terms—CGLIB proxy and JDK dynamic proxy. I knew they were used for method interception, but I wasn’t sure which one was better or why Spring even needed two types.
If you’ve ever wondered about this too, don’t worry. In this post, I’ll break down the key differences between Spring CGLIB vs Dynamic Proxy, when to use each, and why they matter.
Key Takeaways (Short & Sweet)
- JDK Dynamic Proxy works with interfaces, while CGLIB works by subclassing.
- CGLIB is faster but can’t handle final classes/methods.
- Spring automatically picks the best proxy based on your code structure.
Now, let’s dive into the details!
Proxies in Spring
Before we get into CGLIB and dynamic proxies, let’s quickly talk about why Spring uses proxies in the first place.
Imagine you run a coffee shop. You have a cashier who takes orders and a barista who makes the coffee. One day, you decide to monitor sales, so you install a security camera. The camera doesn’t change how orders are taken, but it logs every transaction.
That’s exactly how proxies work in Spring! They wrap around your actual object and allow Spring to add extra behaviors—like logging, security, or transaction management—without modifying your business logic.
JDK Dynamic Proxy vs CGLIB Proxy: What’s the Difference?
Both proxies serve the same purpose but work differently. Here’s a simple breakdown:
Key Differences Between JDK Dynamic Proxy and CGLIB Proxy
| Feature | JDK Dynamic Proxy | CGLIB Proxy |
|---|---|---|
| Works with | Interfaces only | Concrete classes |
| How it works | Implements the interface | Subclasses the class |
| Performance | Slightly slower | Faster due to direct method calls |
| Requires an interface? | Yes | No |
| Can proxy final methods? | No | No |
| Used by default in Spring? | Yes, if an interface is present | Only if no interface is found |
JDK Dynamic Proxy: When and Why?
JDK dynamic proxy is the default choice in Spring if your class implements an interface. This means that Spring creates a proxy that acts as the interface, not the actual class.
Example Code: JDK Dynamic Proxy in Action
public interface CoffeeService {
void makeCoffee();
}
@Service
public class CoffeeServiceImpl implements CoffeeService {
public void makeCoffee() {
System.out.println("Making coffee...");
}
}
Since CoffeeServiceImpl implements CoffeeService, Spring will use a JDK dynamic proxy automatically.
When Should You Use JDK Dynamic Proxy?
- When your class already implements an interface.
- When you don’t need to proxy final methods.
- When you want a lightweight and simple proxy.
CGLIB Proxy: When and Why?
Now, let’s say you don’t have an interface—only a class. What happens then? Well, Spring can’t use JDK dynamic proxies because they require an interface. Instead, it falls back to CGLIB.
CGLIB works by creating a subclass of your class and overriding its methods. This makes it faster than JDK proxies but comes with one catch: It can’t proxy final methods.
Example Code: CGLIB Proxy in Action
@Service
public class TeaService {
public void makeTea() {
System.out.println("Making tea...");
}
}
Since TeaService doesn’t implement an interface, Spring will use CGLIB to create a proxy.
When Should You Use CGLIB Proxy?
- When you don’t have an interface.
- When you need better performance (especially for high-throughput applications).
- When you don’t use final methods.
Which One Should You Choose?
Honestly? You don’t have to. Spring automatically picks the right proxy based on your code. But if you ever want to force CGLIB, you can do so by adding this in your Spring configuration:
@EnableAspectJAutoProxy(proxyTargetClass = true)
This tells Spring to always use CGLIB, even if an interface is present.
When to Use Which Proxy?
| Scenario | Best Proxy to Use |
|---|---|
| Class implements an interface | JDK Dynamic Proxy |
| No interface present | CGLIB Proxy |
| Need high performance | CGLIB Proxy |
| Need to proxy a final method | Neither (not possible) |
| Want to manually control proxy type | Set proxyTargetClass = true in @EnableAspectJAutoProxy |
Performance Comparison: Is CGLIB Really Faster?
A lot of people say CGLIB is faster than JDK dynamic proxies, but is that actually true?
In most real-world applications, you won’t notice much of a difference. However, if you’re making millions of method calls per second, then CGLIB can be slightly faster because it uses direct method calls instead of reflection.
That said, unless performance is a bottleneck, you probably don’t need to worry about it. Spring’s default behavior is optimized for most use cases.
Conclusion:
If I had to summarize everything in one sentence, I’d say: Let Spring decide. Most of the time, you don’t need to worry about choosing between JDK dynamic proxy vs CGLIB proxy.
However, if you’re working on a high-performance application or your class doesn’t have an interface, knowing how these proxies work can help you make better design decisions.
FAQs
What is the main difference between CGLIB and JDK Dynamic Proxy?
JDK proxies work with interfaces, while CGLIB works by subclassing classes.
Which proxy is the default in Spring?
Spring uses JDK Dynamic Proxy by default if an interface is present. Otherwise, it uses CGLIB.
Can I force Spring to use CGLIB instead of JDK Proxy?
Yes, by adding @EnableAspectJAutoProxy(proxyTargetClass = true) in your configuration.
Is CGLIB faster than JDK Dynamic Proxy?
Yes, in some cases, but the difference is small in most real-world applications.
Can CGLIB proxy final methods?
No, CGLIB cannot proxy final methods or classes.
When should I use JDK Dynamic Proxy?
Use it when your class implements an interface and you want a simple, lightweight proxy.
When should I use CGLIB?
Use it when your class doesn’t have an interface and you need better performance.