Dynamic Proxies in Java

Java dynamic proxies let you create proxy behavior at runtime for interface-based types.

Why They Exist

Dynamic proxies are useful when the access concern is the same across many targets:

• timing
• logging
• authorization checks
• tracing

Instead of writing one proxy class per interface, Java routes calls through an InvocationHandler.

1InvocationHandler handler = (proxy, method, args) -> {
2    long start = System.nanoTime();
3    try {
4        return method.invoke(target, args);
5    } finally {
6        System.out.println(method.getName() + " took " + (System.nanoTime() - start));
7    }
8};

Limits

Dynamic proxies work naturally for interfaces. They are not a universal replacement for explicit proxy classes. If the access rule is domain-specific and important to read directly, a named hand-written proxy may still be clearer.

Review Rule

Use dynamic proxies for reusable cross-cutting access behavior, not for hiding core domain design.