错误写法：
cxt = new ClassPathXmlApplicationContext();
productService = (ProductService)cxt.getBean("productTypeServiceBean");
正确写法：
cxt = new ClassPathXmlApplicationContext("beans.xml");
productService = (ProductService)cxt.getBean("productTypeServiceBean");
原文：http://www.cnblogs.com/lomomiao/p/4269519.html