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Dynamic Proxy

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

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Dynamic Proxy

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  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

  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

  3. Dynamic Proxy: Invocation // invocation examples ((Foo)proxyInstance).bar(); ((Foo1)proxyInstance).bar1(); Good Java Programming

  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 Good Java Programming

  5. Proxy Pattern • Provides a surrogate or placeholder for another object to control access to it. Good Java Programming

  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

  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

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