Uniform proxies for Java

Abstract

The proxy abstraction has a longlasting tradition in object settings. From design pattern to inherent language support, from remote method invocations to simple forms of behavioral reflection -incarnations as well as applications of proxies are innumerable.Since version 1.3, Java supports the concept of dynamic proxy. Such an object conforms to a set of types specified by the program and can be used wherever an expression of any of these types is expected, yet reifies invocations performed on it. Dynamic proxies have been applied to implement paradigms as diverse as behavioral reflection, structural conformance, or multi-methods. Alas, these proxies are only available "for interfaces". The case of creating dynamic proxies for a set of types including a class type has not been considered, meaning that it is currently not possible to create a dynamic proxy mimicking an instance of a given class. This weakness strongly limits any application of dynamic proxies.In this paper we unfold the current support for dynamic proxies in Java, assessing it in the light of a set of generic criteria for proxy implementations. We present an approach to supporting dynamic proxies "for classes" in Java, consisting in transformations performed on classes at load-time, including a generic scheme for enforcing encapsulation upon field accesses. These transformations seemlessly extend the scope of the current support for dynamic proxies. We discuss the precise benefits and costs of our extension in terms of the criteria introduced, and illustrate the usefulness of uniformly available proxies by implementing future method invocations both safely and transparently.

Handles: Behavior-propagating first class references for dynamically-typed languages

“…For example, all methods defined in the root class Object cannot be intercepted as they are not defined in an interface. Uniform proxies for Java [Eug06] is an approach to provide dynamic proxies that work for the whole interface of arbitrary classes. Uniform proxies can thus mimic arbitrary objects.…”

Efficient proxies in Smalltalk

“…This means that, if you want to create a proxy for a domain class, you are forced to create an interface for it. Eugster [11] proposed a solution which provides proxies for classes. There is also a third-party framework based on bytecode manipulation called CGLib [9] which provides proxies for classes.…”

“…A large number of scenarios and applications [11] have embraced and used the Proxy Design Pattern [12].…”

“…Some of them, e.g., Java Dynamic Proxies [11,14] even requires that at creation time the user provides a list of Java interfaces for capturing the appropriate messages.…”

Flexible and Efficient In-Vivo Enhancement for Grid Applications

“…Another advantage of Virtual Superclass is its generality. The existing state of the art in enabling proxy indirection [10] creates subclass-based proxies, which have limitations for final classes and methods. By contrast, Virtual Superclass works for any class or method, as the final modifier does not constrain the creation of superclasses.…”