spring的验证方法中初次使用这个类，请问什么是GlobalError？不太理解
http://blog.csdn.net/olanmomo/article/details/50530352
errors.pushNestedPath这个方法是做什么用的？官方API看不太明白
void pushNestedPath(String subPath)
Push the given sub path onto the nested path stack.
A popNestedPath() call will reset the original nested path before the corresponding pushNestedPath(String) call.
Using the nested path stack allows to set temporary nested paths for subobjects without having to worry about a temporary path holder.
For example: current path "spouse.", pushNestedPath("child") -> result path "spouse.child."; popNestedPath() -> "spouse." again.
Parameters:
subPath - the sub path to push onto the nested path stack
See Also:
popNestedPath()