为什么使用Required注解会有异常？
@Required
public void setInjectionDAO(InjectionDAO injectionDAO) {
this.injectionDAO = injectionDAO;
}
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'injectionServiceImpl' defined in file [D:\Myeclipse\Workspace\SpringCourse\bin\test8\InjectionServiceImpl.class]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanInitializationException: Property 'injectionDAO' is required for bean 'injectionServiceImpl'
