Java Language Reflection API Dynamic Proxies
Example
Dynamic Proxies do not really have much to do with Reflection but they are part of the API. It's basically a way to create a dynamic implementation of an interface. This could be helpful when creating mockup services.
A Dynamic Proxy is an instance of an interface that is created with a so-called invocation handler that intercepts all method calls and allows the handling of their invocation manually.
public class DynamicProxyTest {
public interface MyInterface1{
public void someMethod1();
public int someMethod2(String s);
}
public interface MyInterface2{
public void anotherMethod();
}
public static void main(String args[]) throws Exception {
// the dynamic proxy class
Class<?> proxyClass = Proxy.getProxyClass(
ClassLoader.getSystemClassLoader(),
new Class[] {MyInterface1.class, MyInterface2.class});
// the dynamic proxy class constructor
Constructor<?> proxyConstructor =
proxyClass.getConstructor(InvocationHandler.class);
// the invocation handler
InvocationHandler handler = new InvocationHandler(){
// this method is invoked for every proxy method call
// method is the invoked method, args holds the method parameters
// it must return the method result
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
String methodName = method.getName();
if(methodName.equals("someMethod1")){
System.out.println("someMethod1 was invoked!");
return null;
}
if(methodName.equals("someMethod2")){
System.out.println("someMethod2 was invoked!");
System.out.println("Parameter: " + args[0]);
return 42;
}
if(methodName.equals("anotherMethod")){
System.out.println("anotherMethod was invoked!");
return null;
}
System.out.println("Unkown method!");
return null;
}
};
// create the dynamic proxy instances
MyInterface1 i1 = (MyInterface1) proxyConstructor.newInstance(handler);
MyInterface2 i2 = (MyInterface2) proxyConstructor.newInstance(handler);
// and invoke some methods
i1.someMethod1();
i1.someMethod2("stackoverflow");
i2.anotherMethod();
}
}
The result of this code is this:
someMethod1 was invoked!
someMethod2 was invoked!
Parameter: stackoverflow
anotherMethod was invoked!
