Status: New
Owner: ----
New issue 684 by [email protected]: Possibility to save state of
InterceptorStackCallback in MethodInvocation implementation
http://code.google.com/p/google-guice/issues/detail?id=684
When writing a MethodInterceptor the state of the MethodInvocation passed
in by Guice is only valid before and after proceed has been called. And
before the invoke method returns.
i.e.
@Override public Object invoke(final MethodInvocation invocation) throws
Throwable {
// invocation valid
Object result = invocation.proceed(); // invocation changes for the
duration of the proceed call
// invocation valid
return result;
// invocation changes due to return
}
The reason for this is the use of the mutable "index" field in the
InterceptedMethodInvocation class.
The implementation of "proceed()" recursively passes itself to each of the
interceptors. Effectively "index" is working as a stack pointer.
The consequence of this is that I cannot keep a reference to the
MethodInvocation object and use it somewhere else. For example, I want to
write an method interceptor that executes the intercepted method in a
different thread. An immutable implementation of MethodInvocation would be
preferable.
For example copying the InterceptedMethodInvocation before each invocation
would solve this problem by making the MethodInvocation more like an
immutable object. Like this:
private class InterceptedMethodInvocation implements MethodInvocation {
final Object proxy;
final Object[] arguments;
final MethodProxy methodProxy;
public InterceptedMethodInvocation(final Object proxy, final
MethodProxy methodProxy,
final Object[] arguments) {
this(proxy, methodProxy, arguments, -1);
}
public InterceptedMethodInvocation(final Object proxy, final
MethodProxy methodProxy,
final Object[] arguments, int index) {
this.proxy = proxy;
this.methodProxy = methodProxy;
this.arguments = arguments;
this.index = index;
}
public Object proceed() throws Throwable {
try {
int nextIndex = index + 1;
return nextIndex == interceptors.length
? methodProxy.invokeSuper(proxy, arguments)
: interceptors[nextIndex].invoke(new
InterceptedMethodInvocation(proxy, methodProxy, arguments, nextIndex));
} catch (final Throwable t) {
pruneStacktrace(t);
throw t;
}
}
public Method getMethod() {
return method;
}
public Object[] getArguments() {
return arguments;
}
public Object getThis() {
return proxy;
}
public AccessibleObject getStaticPart() {
return getMethod();
}
}
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