返回的响应类型反而是通过requestMapping指定:
@RequestMapping(value = "/someurl/suburl", produces = "application/xml")
...
@RequestMapping(value = "/someurl/suburl", produces = "application/json")
方法返回值可以是String也可以是复杂类型, 但指定请求响应为xml时, 如果返回复杂类型, 该类型好像是要用javax.xml.bind.annotation.*下的注解映射成XML元素(/*没去试*/)