有时候，在SPRING中两个类互相含有对方的声明，一般情况这是不允许并且极可能是有错误的。
会报这个错：
org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name ‘***’: Bean with name ‘***’ has been injected into other beans [***, ***]in its raw version as part of a circular reference,
but has eventually been wrapped (for example as part of auto-proxy creation). This means that said other beans do not use the final version of the bean. This is often the result of over-eager type matching - consider using ‘getBeanNamesOfType’ with the ‘allowEagerInit’ flag turned off, for example.
但有时候这正是我们想要的，考虑这种情况：
我们用一个ManagerFactory来包含所有Manager的声明，以便在程序中用到多个Manager的地方，一个入口集中访问。但是，可能某个Manager本身就需要用到其它几个Manager，进而用到ManagerFactory。这时，我们可以这样声明即可：
<bean />
来源：http://www.blogjava.net/alwayscy/archive/2008/02/24/181726.htm