Package com.thoughtworks.proxy.toys.decorate

A toy to decorate the interaction with another object.

See: Description

Interface Summary

Interface	Description
InvocationDecorator	Decorates a method invocation

Class Summary

Class	Description
Decorating	Toy factory to create proxies decorating an object in an AOP style.
DecoratingInvoker	Invoker implementation for the decorating proxy.
InvocationDecoratorSupport	Identity implementation for a InvokerDecorator.

Package com.thoughtworks.proxy.toys.decorate Description

A toy to decorate the interaction with another object.

The package provides a proxy factory creating proxies, that are used to decorate the interaction with another object as done with AOP. Main component is the Decorating toy, a utility class creating these proxies. Such a proxy contains an instance of a DecoratingInvoker that defines the additional functionality. A DecoratingInvoker is invoked for each method call on the proxy, for each value returned from a proxied method, for each exception thrown from the original object's method and for each occuring exception invoking the method in the original object.

The following example decorates an iterator of a list of strings to convert every String into an Integer:

List list = Arrays.asList(new String[]{"1", "2", "3"});
Iterator intIter = (Iterator)Decorating.object(Iterator.class, list.iterator(), 
        new InvocationDecoratorSupport() {
        public Object decorateResult(Object proxy, Method method, Object[] args, Object result) {
                if (method.getName().equals("next"))
                                return Integer.valueOf((String)result);
                        else
                                return result;
                }
        });
while(intIter.hasNext()) {
        Integer i = (Integer)intIter.next();
        System.out.println(i);
}

The next example implements a simple trace mechanism for a single object. Since we proxy here a real object instead of an interface, we have to use the CglibProxyFactory:

File file = new File(".");
File decoratedFile = (File)Decorating.object(new Class[]{File.class}, file, new InvocationDecoratorSupport() {
    public Object[] beforeMethodStarts(Object proxy, Method method, Object[] args) {
        System.out.print("Called: " + method.getName());
        return super.beforeMethodStarts(proxy, method, args);
    }
    public Object decorateResult(Object proxy, Method method, Object[] args, Object result) {
        System.out.println(" ==> " + result);
        return result;
     }
}, new CglibProxyFactory());
decoratedFile.exists();
decoratedFile.isFile();
decoratedFile.isDirectory();

For a more sophisticated trace mechanism, have a look at the Echoing toy