Scala get classtag from class instance

I need to write a generic method to get all fields of an object and it's value, the class of this object may contains ClassTag, so we should find a way to get it as well, is any way good way ? the difficulty is we don't know the class ahead, it may contains ClassTag (zero to many), It may not.

For example,

class A(x : Int) {}

a = new A(1)

We should output x => 1

class B[T: ClassTag]() {}

b = new B[Float]()

We should output _$1 = Float