该异常的抛出，表明代码企图把对象的类型转换成一个子类，而该对象并不是这个子类的实例。
Thrown to indicate that the code has attempted to cast an object to a subclass of which it is not an instance.
业务对象映射：可以使用业务对象映射将某种类型的业务对象转换成另一种类型的业务对象。
Business Object maps: You use a Business Object map to translate one type of Business Object into another type of Business Object.
为了理解这一点，记住标记中的任何内容都必须转换为某种类型的对象。
To understand this, remember that everything in your markup has to be turned into an object of some type.
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