spring 能不能在方法内决定返回类型

感觉ResponseEntity可以解决题主的问题，但并不推荐这样做，下面只是一个例子。

@RequestMapping("/entity")
@ResponseBody
public ResponseEntity<String> handle(HttpEntity<byte[]> requestEntity) throws UnsupportedEncodingException {
    System.out.println(requestEntity.getHeaders().getFirst("MyRequestHeader"));
    System.out.println(Arrays.toString(requestEntity.getBody()));

    HttpHeaders responseHeaders = new HttpHeaders();
    responseHeaders.set("MyResponseHeader", "MyValue");
    return new ResponseEntity<>("Hello World", responseHeaders, HttpStatus.CREATED);
}

代码乱乱的，写着不顺心，改着还闹心。
不如用headers区分一下，同一个URL不同headers映射到不同方法。
比如:

@RequestMapping(value = "/",method = RequestMethod.GET, produces = MediaType.APPLICATION_XML_VALUE,headers = {"a=1"})
public String index(Map<String, Object> map) {
    map.put("title", "");
    map.put("keywords", "");
    map.put("description", "");

    return "index";
}

@RequestMapping(value = "/",method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE,headers = {"a=1"})
@ResponseBody
public Map indexJson(Map<String, Object> map) {
    map.put("title", "");
    map.put("keywords", "");
    map.put("description", "");

    return map;
}