You can only claim you know Spring if you fully understand the Proxy design pattern and how the framework uses it to do its magic. Join this live coding session to explore 6 ways of intercepting method calls that you can use to cast your own spells and dramatically simplify your codebase. Grab a strong coffee and prepare yourself for a whirlwind of **live-coding**, interwoven with **deep theoretical concepts and implementation details** that you need to master if you are using the Spring Framework. We’ll start from a Decorator pattern implementation, proving 2 ways to wire it with Spring, then move to bare-hands interface proxies, concrete classes proxies, @Aspect applied to custom annotations, plus some standard off-the-shelf Spring aspects. Join this talk and learn real-world best practices to use with Aspects, design hints, under-the-hood implementation details, debugging tips, and performance impact of aspects. All in an interactive, entertaining, and extremely dynamic session.

1. victorrentea@gmail.com ♦ ♦ @victorrentea ♦ VictorRentea.ro
All the code is available on the branch JAX_Mainz on https://github.com/victorrentea/spring

2. Victor Rentea
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5. 3
5 © VictorRentea.ro
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class A {
private B b;
...
}
class BImpl
implements B {
m() {} ...
}
interface B {
m(); ...
}
Interface Proxy
has a
:A
B
:BImpl
implem
Static
Runtime

6. 36 © VictorRentea.ro
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class A {
private B b;
...
}
class BImpl
implements B {
m() {} ...
}
interface B {
m(); ...
}
Interface Proxy
has a
:A
B
:BImpl
implem
call
Static
Runtime
implem
proxy
m() {}
Created at run-time with
java.lang.reflect.Proxy

7. 37 © VictorRentea.ro
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class A {
private B b;
...
}
interface B {
m(); ...
}
Class Proxy
has a
Static
Runtime
class B {
{ }
:A
B
:B
call
proxy
m() {}
The bytecode of a subclass
is generated in memory by (eg CGLIB)
extends
Different InstanceS

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Every time you don’t understand how Spring does something…
it's a Proxy
@Cacheable
@Transactional
@Aspect
@Async
@Secured / @PreAuthorize
@Retryable
Request/Session/Thread scope
…
The Magic of Spring

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Dependency Injection is great because
1 Classes are easier to break
3 Proxies can be given to you transparently
2 Cleaner to test

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:B
proxy
m() {}
Different InstanceS
Local Method Calls
don't get Proxied!
@Override
m() {}
Class Proxy Pitfalls
final
ignored:
final class
crash:
The default way
in Spring
You have to take
a reference to B
from Spring

12. @ Victo
r
Rentea
42
•A method of a non-Spring bean?
• Think new
•A final method/class?
• For a class-proxy:
•A static method?
•Field access?
•A local method call?
Can Spring AOP Intercept…
NO!
NO!
Spring AOP can only intercept method calls
NO!
Well…
Actually…
You know…
You can do any of that via:
Bytecode Enhancement
(compile-time hacking)
Or Instrumentation
(classload-time hacking)
NO!!!
NO!
How could it be overridden?
https://github.com/dsyer/spring-boot-aspectj#

13. @VictorRentea
43
proxy
methodWithTx();
myselfProxied.methodWithTx();
War Stories
@Transactional(propagation = REQUIRES_NEW)
public void methodWithTx() {
@Autowired
private CurrentClass myselfProxied;
--or–
move methodWithTx() to another @Autowired bean
--or--
CurrentClass myselfProxied =
(CurrentClass)AopContext.currentProxy();
--or--
transactionTemplate.execute(s->methodWithTx());
https://stackoverflow.com/questions/3423972/spring-transaction-method-call-by-the-method-within-the-same-class-does-not-wo

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No More Magic

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Spring + nativeimage?
45
•Serverless with Spring Cloud Function
•Cheaper hosting of your Spring microservices
•Good fit with Kubernetes platforms like VMware Tanzu
https://spring.io/blog/2021/03/11/announcing-spring-native-beta
Niche?
https://github.com/spring-projects-experimental/spring-native

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nativeimage does NOT support
class-proxies (CGLIB)
Only JDK (interface-) proxies work,
via a Maven Plugin doing Ahead-Of-Time analysis

17. 47 © VictorRentea.ro
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@Cacheable -> CacheManager
@Transactional -> TransactionTemplate
@Async -> executor.submit()
@PreAuthorize/@RolesAllowed
-> SecurityContextHolder.getContext()...
@Retryable -> RetryTemplate
Programmatic Alternatives to Annotations

18. @VictorRentea
48
Functional Programming vs AOP
"Execute Around" Pattern
transactionTemplate.execute(this::methodInNewTx);
(Use JFR instead)

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49
The Hamburger Problem

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50
Average Error (99.9%) Unit
Cache Method 357.7 ± 11.7
us/op
Decorator 355.1 ± 6.0
Interface Proxy 398.7 ± 28.0
Class Proxy 386.9 ± 17.5
Class Proxy / BPP 373.9 ± 36.0
@Cacheable 8109.8 ± 1097.5
Performance
Details? Run it yourself: https://github.com/victorrentea/proxy-fairy-performance

21. @VictorRentea
51
Writing Custom Aspects

22. @VictorRentea
52
@annotation(my.proj.Logged)
annotation-based weaving
Custom Aspects - Best Practices
@Around("@within(my.proj.Facade)")
public Object logAround(ProceedingJoinPoint point) { … }
make them visible
@Facade
public class ExpensiveOps {
@Logged
public Boolean isPrime(int n) {…}
}

23. @VictorRentea
53
Custom Aspects - Best Practices
"execution(* com.mycomp.proj.facade.*.*(..))"
is less magic than
package names
or
class name patterns
"execution(* com.mycomp..*DAO.*(..))"
annotation-based weaving

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keep them light
Custom Aspects - Best Practices
synchronized
files
database
http
don't intercept insane-rate calls

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Annotation-based AOP can feel like changing the language
Make everyone in the team comfortable with it
(think twice before changing the proxy default behavior)
Don't fear performance
(as long as you don't apply it to 100% of methods, and you keep them light)
Consider Alternatives
When interfering with the design
The Moral?

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