Annotate part of a method implementation using AspectJ - aspectj

Question

I have many classes overriding equals for object comparison. For each equals implementation, it uses String .equals which is case sensitive. I'm wondering if it is possible to use AspectJ to simply replace the .equals with .equalsIgnoreCase in each method?
Alternatively, if the above case is not possible, can we use AspectJ to intercept the class to use my own String .equals implementation? (without changing the method implmentation)

Answer 1

You want the String.equals(Object anObject) method to be rerouted to equalsIgnoreCase(String) for every occurence of it in your package, correct?
The Pointcut for it will need to intercept calls to equals (call(boolean equals(Object))), within your packages (within(your.packages.*)) and provide both target (target(sourceString)) and parameter (args(compareString)), so it should look like this:
#Pointcut("call(boolean equals(Object)) && args(compareString) && target(sourceString) && within(your.packages.*)")
protected void equalsPointcut(final Object compareString, final String sourceString) {}
The advice using that Pointcut will have to be an around-advice that skips the call to equals and does it's own call to equalsIgnoreCase instead:
#Around("equalsPointcut(compareString, sourceString)")
public Object around(final ProceedingJoinPoint joinPoint, final Object compareString, final String sourceString)
throws Throwable {
System.out.println("Aspect!");
return sourceString.equalsIgnoreCase(compareString != null ? compareString.toString() : null);
}
The sysout is only there to check that the aspect is actually used and should of course be removed in an actual use case.
My test looks like this:
public static void main(final String[] args) {
String a = "Blaaaa";
String b = "BLAAAA";
System.out.println(a.equals(b));
Object c = new Object();
System.out.println(c.equals(b));
}
And it produces the output:
Aspect!
true
false
Note that a.equals(b) is rerouted to equalsIgnoreCase (since it's target is a String), but c.equals(b) is not (since it's target is an Object!).
I hope this answers your question. Happy coding! ;)