1. Dynamic Proxy Proxy: Addition to the Java 1.3 reflection package:
implements a list of interfaces specified at runtime
can be used as if the Proxy class implemented these interfaces!
when invoked passes the “method invocation” to an implementation of the InvocationHandler
how does this affect the stub-skeleton design?
Good Java Programming
6/24/2018

2. Dynamic Proxy: Instantiation
InvocationHandler handler =
new GenericSerializationHandler();
Foo1 proxyInstance = (Foo1) Proxy.newProxyInstance(
Foo.class.getClassLoader(),
new class[ ] { Foo.class,
Foo1.class},
handler);
Good Java Programming
6/24/2018

3. Dynamic Proxy: Invocation
// invocation examples
((Foo)proxyInstance).bar();
((Foo1)proxyInstance).bar1();
Interface Foo has a method named bar
Interface Foo1 has a method named bar1
Good Java Programming
6/24/2018

4. Dynamic Proxy: Invocation Handler
public GenericSerializationHandler implements InvocationHandler { …
public Object invoke(Object proxy, Method m, Object[] args) throws Throwable {
String methodName = m.getName();
Class className = m.getDeclaringClass();
if (className.equals(Foo.class) &&
methodName.equals(“bar”)) {
System.out.print(“Method bar called”); }
// className: interface on which the method was invoked
// proxy: proxy instance on which the method was invoked
// args: value of arguments in the methods
Method in the Invocation Handler that handles all calls
Good Java Programming
6/24/2018

5. Proxy Pattern
Provides a surrogate or placeholder for another object to control access to it.
Good Java Programming
6/24/2018

6. Proxy Pattern: Variations
Remote Proxy: controls access to a remote object
proxy acts as a local representative for an object in a different JVM
Virtual Proxy: controls access to a resource that is expensive to create
Defers creation of the object until needed
Once the object is created, proxy delegates requests to the real object
Caching Proxy
maintains a cache of previously created objects and returns cached objects whenever appropriate
Protection Proxy: controls access to a resource based on access rights
How can this be implemented using Dynamic Proxy in Java?
Good Java Programming
6/24/2018

7. Virtual Proxy Defers creation of the object until needed
Once the object is created, proxy delegates requests to the real object
Example:
Creates a generic icon for an image, while waiting for the image to be retrieved from the network
Once the image is received, replaces the generic one with the actual image
Good Java Programming
6/24/2018