JDK vs CGLib in Spring AOP: Which Proxy Is Faster?

Background

During a recent interview a candidate was asked which dynamic proxy—JDK or CGLib—offers higher efficiency in Spring AOP. This article summarizes the key points for reference.

Basic Concepts

Spring AOP can generate proxies using two mechanisms: JDK dynamic proxies (interface‑based) and CGLib (subclass‑based). JDK proxies rely on java.lang.reflect.Proxy and InvocationHandler, while CGLib uses bytecode generation to create a subclass that intercepts method calls.

JDK vs CGLib Differences

JDK proxy creates an implementation of the target’s interfaces; it cannot proxy classes without interfaces.

CGLib creates a subclass of the target class, allowing proxying of concrete classes (except final ones).

Performance Comparison – Textbook Description

Common wisdom states that CGLib proxies execute faster (up to 10×) but take longer to create (about 8× slower) compared to JDK proxies. Consequently, CGLib is preferred for singleton or pooled instances, while JDK proxies suit lightweight, frequently created objects.

Performance Test Setup

The following Java files were used for benchmarking:

Various Java classes (illustrated in images).

Target.java

TargetImpl.java

JdkDynamicProxyTest.java

CglibProxyTest.java

ProxyPerformanceTest.java

Images of the source code are shown below:

Test Results

Across Java 1.6, 1.7, and 1.8 the following observations were made:

In JDK 1.6 and 1.7, JDK proxies were slower than CGLib proxies, but the gap was far smaller than the textbook‑claimed tenfold difference.

In JDK 1.8, JDK proxies consistently outperformed CGLib proxies after multiple runs.

Thus, while JDK proxies have improved in newer JVMs, the choice still depends on the specific scenario.

Conclusion

The experiments show that JDK dynamic proxies are slower than CGLib in older Java versions, but in Java 1.8 they become faster. Developers should select the proxy type based on whether the target is an interface implementation (prefer JDK) or a concrete class (use CGLib), considering creation cost and runtime performance.

References: 1. https://blog.csdn.net/qq1723205668/article/details/56481476 2. https://blog.csdn.net/xiangbq/article/details/49794335