URGENT: Catch a NoClassDefError within a method at runtime?

Question

Hi there,
I have a Class A that creates an instance of Class B in method mA().
At compile time, Class A and B are both included in the CLASSPATH.
However, at runtime, Class B is removed from the CLASSPATH resulting in a NoClassDefError as expected.
NOTE: How do I gracefully handle a condition wherein I can dynamically catch this NoClassDefError? According to the javadoc, a NoClassDefError is thrown by the JVM or by the ClassLoader instance?
Hence, I have...
class A
void mA()
try {
B b = new B();
} catch (Throwable th)
System.out.println("Gracefully caught exception");
th.printStackTrace();
Note: Upon execution of (new A()).mA(), I get a console message...
Exception in thread "xyz" java.lang.NoClassDefFoundError: B
(This was probably displayed by the JVM)
This is NOT what I wanted.
I was hoping to have this gracefully caught in my try catch block.
I have the following restrictions...
1. The instance of B cannot be created using reflection. This is user code written within my application and I cannot tell him how to write code due to Java's limitation of not being able to catch a NoClassDefError at runtime.
2. I cannot use a custom class loader to detect a failure in loading this class because this application is expected to work in multiple environments containing variable parent class loader definitions.
How do I do this?

Answer 1

That exception is the result of loading a class not
calling any methods (including the constructor.)I definitely agree :-)
... and the class being loaded is class B. Now, my
point was that maybe the B class isn't loaded when
mA() is called, but rather when the first A is
created. (Which would load class A, which might
possibly trigger loading class B).I believe the spec disallows throwing an exception when the class is loaded for an instance that exists solely in a method. The reality of this is that it is much easier for VMs not to resolve classes until the method actually runs.
However, it can resolve it in the method any place it wants - like before try block starts executing. You can test this by creating a second method that actually calls B. Then wrap that method call in a try block inside of the constructor.