CODEWITHSUNDEEP
javagenericsproxy-classes
Grim
Grim

Reputation: 2026

Proxying with Generics

I use java.lang.reflect.Proxy to proxy objects.

I have this class:

public class TransportableImpl extends Transportable{
  public class OrderInvoker extends InvocationHandler{
           ...
  }
}

Here i build the Proxy:

Transportable t = new TransportableImpl();
Order myOrder = new OrderImpl();
Class proxyClass = Proxy.getProxyClass(getClass().getClassLoader(), Transportable.class, Order.class);
Object serializable = proxyClass.getConstructor(new Class[]{InvocationHandler.class}).newInstance(t.new OrderInvoker(myOrder));

Problem is: Class is raw type and 

Class<? extends Order & Transportable> proxyClass =
     (Class<? extends Order & Transportable>) 
     Proxy.getProxyClass(getClass().getClassLoader(), 
     Transportable.class, Order.class);

is hard to read.

Any ideas?

Upvotes: 2

Views: 1548

Answers (1)

Sotirios Delimanolis
Sotirios Delimanolis

Reputation: 280102

The Proxy#getProxyClass(ClassLoader, Class) method is declared as 

public static Class<?> getProxyClass(ClassLoader loader,
                                     Class<?>... interfaces)

Its return type is therefore Class<?>. The normal syntax would be

Class proxyClass<?> = Proxy.getProxyClass(getClass().getClassLoader(), Transportable.class, Order.class);

Technically you could do (with a warning)

public <T extends Order & Transportable> void doSomething() {
    Class<T> proxyClass = (Class<T>) Proxy.getProxyClass(Driver.class.getClassLoader(),
            Transportable.class, Order.class);
}

but that gains you nothing as you will pretty much never need to use that T variable. The Class class provides very little methods that makes use of it, namely getConstructor(Class...) and newInstance(). But again, the whole point of reflection is that you only know the class types at run time, not at compile time where generics are useful.

Upvotes: 2

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