How to get parameter name in aspectj advice class? - reflection

Question

I am asking this question with my limited knowledge of java reflection and AOP.
Background:
I am using annotation based advice in my Java 7 application. Further to get the method parameter which I need to use in my advice I am using spring EL. See below examples:
In first example i want to use second parameter to do my work, whereas in second example I am using a POJO and want to use its "id" field.
#MyAnnotation(param = "args[1]")
public void someMethod(int param1, String param2) {
return null;
}
#MyAnnotation(param = "args[0].id")
public void someMethod(SomeObject someObject) {
return null;
}
But what I actually want is, to get my hands on the parameter names in my AOP. So that I can use #MyAnnotation(param = "param1") or #MyAnnotation(param = "someObject.id") instead.
From what I have known, you can not get parameter name using reflection. But recently I came across Spring cache abstraction(link), where I see:
#Cacheable(cacheNames="books", key="#isbn")
public Book findBook(ISBN isbn, boolean checkWarehouse, boolean includeUsed)
Can someone put some light here, how I can achieve similar behavior.

Answer 1

See MethodBasedEvaluationContext and ParameterNameDiscoverer.
CacheEvaluationContext is a subclass of MethodBasedEvaluationContext.
Code here...
// Expose indexed variables as well as parameter names (if discoverable)
String[] paramNames = this.parameterNameDiscoverer.getParameterNames(this.method);
int paramCount = (paramNames != null ? paramNames.length : this.method.getParameterCount());
int argsCount = this.arguments.length;
for (int i = 0; i < paramCount; i++) {
Object value = null;
if (argsCount > paramCount && i == paramCount - 1) {
// Expose remaining arguments as vararg array for last parameter
value = Arrays.copyOfRange(this.arguments, i, argsCount);
}
else if (argsCount > i) {
// Actual argument found - otherwise left as null
value = this.arguments[i];
}
setVariable("a" + i, value);
setVariable("p" + i, value);
if (paramNames != null) {
setVariable(paramNames[i], value);
}
}