關於expected single matching bean but found 2的問題
問題：
org.springframework.context.support.AbstractApplicationContext refresh
警告: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userLoginServlet' defined in class path resource [spring.xml]: Unsatisfied dependency expressed through bean property 'userDao'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'cn.tedu.spring.UserDao' available: expected single matching bean but found 2: userDao,subUserDao
Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userLoginServlet' defined in class path resource [spring.xml]: Unsatisfied dependency expressed through bean property 'userDao'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'cn.tedu.spring.UserDao' available: expected single matching bean but found 2: userDao,subUserDao
***——>Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'cn.tedu.spring.UserDao' available: expected single matching bean but found 2: userDao,subUserDao
分析：使用了根據類型(byType)的自動裝配方式，這種自動裝配要求最多只有1個匹配類型的對象，但是，在Spring容器中卻出現了2個這樣的對象，Spring就不知道應該裝配哪一個了，就會出現錯誤！
解決方案：使得Spring只管理其中1個類型的對象，或者，使用byName方式來裝配。
異常：NoUniqueBeanDefinitionException：不唯一的Bean匹配異常