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 {@linkplain com.thoughtworks.proxy.toys.decorate.Decorating Decorating toy}, a utility class creating these proxies. Such a proxy contains an instance of a {@link com.thoughtworks.proxy.toys.decorate.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 {@link com.thoughtworks.proxy.factory.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 {@linkplain com.thoughtworks.proxy.toys.echo Echoing toy}