Proxy Interfaces In Java

#java #programming

Java provides a static method Proxy.newProxyInstance as part of it’s Reflection API. This static method returns a proxy class for a given set of interfaces. It requires only 3 things:

  1. A class loader
  2. A list of interfaces that this proxy should implement
  3. An InvacationHandler. This is like a callback which is invoked when methods on this proxy are called.

Proxy Class Properties

  1. The proxy classes are public, final and non-abstract
  2. This proxy classes extend java.lang.reflect.Proxy
  3. Implements all interfaces provided (in the order) at the time of creation
  4. proxy instanceof Foo returns true and (Foo) proxy succeeds without any ClassCastExceptions
public interface Account {
    BigInteger computeBalance(BigInteger considerDeductions);

InvocationHandler handler = new InvocationHandler() {
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println(method); // the method that is being called
        System.out.println(args); // parameters passed to that method
        return BigInteger.ONE;
Account accountProxy = (Account) Proxy.newProxyInstance(
    new Class[]{


Use Cases

  1. Mockito and similar libraries
  2. When you want to make batched calls