OnJava8-Examples/typeinfo/SimpleDynamicProxy.java

// typeinfo/SimpleDynamicProxy.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
import java.lang.reflect.*;

class DynamicProxyHandler implements InvocationHandler {
  private Object proxied;
  DynamicProxyHandler(Object proxied) {
    this.proxied = proxied;
  }
  @Override public Object
  invoke(Object proxy, Method method, Object[] args)
  throws Throwable {
    System.out.println(
      "**** proxy: " + proxy.getClass() +
      ", method: " + method + ", args: " + args);
    if(args != null)
      for(Object arg : args)
        System.out.println("  " + arg);
    return method.invoke(proxied, args);
  }
}

class SimpleDynamicProxy {
  public static void consumer(Interface iface) {
    iface.doSomething();
    iface.somethingElse("bonobo");
  }
  public static void main(String[] args) {
    RealObject real = new RealObject();
    consumer(real);
    // Insert a proxy and call again:
    Interface proxy = (Interface)Proxy.newProxyInstance(
      Interface.class.getClassLoader(),
      new Class[]{ Interface.class },
      new DynamicProxyHandler(real));
    consumer(proxy);
  }
}
/* Output:
doSomething
somethingElse bonobo
**** proxy: class $Proxy0, method: public abstract void
Interface.doSomething(), args: null
doSomething
**** proxy: class $Proxy0, method: public abstract void
Interface.somethingElse(java.lang.String), args:
[Ljava.lang.Object;@1b84c92
  bonobo
somethingElse bonobo
*/