使用SpringBoot的RestController來寫接口后，不再使用httpServletResponse來操作請求的輸出了，所以返回圖片需要換一種方式

修改@RequestMapping

在RequestMapping / GetMapping新增produces屬性，并把方法的返回值改為字節(jié)流byte[]類型：

@GetMapping(value = "/image",produces = MediaType.IMAGE_JPEG_VALUE)
public byte[] getPicture() throws Exception {...}

實際邏輯的代碼實現

public byte[] getPicture() throws Exception {
    OutputStream out = null;
    File file = new File("path/1.jpeg");
    FileInputStream inputStream = new FileInputStream(file);
    byte[] bytes = new byte[inputStream.available()];
    inputStream.read(bytes, 0, inputStream.available());
    return bytes;
}

動態(tài)設置Content-type

如果邏輯中還需要實現鑒權 / 限流 / not found等報錯;
分別讓正常請求返回image/jpeg圖片在異常時返回application/json錯誤信息，則可以如下改造：

@GetMapping("ct/{id}")
public ResponseEntity<Object> getPictureIfExist(@PathVariable Integer id) {
        HttpHeaders headers = new HttpHeaders();
        try {
            //設置Content-type為image/jpeg
            headers.add(HttpHeaders.CONTENT_TYPE, MediaType.IMAGE_JPEG_VALUE);
            File file = new File("path/1.jpeg");
            FileInputStream inputStream = new FileInputStream(file);
            byte[] bytes = new byte[inputStream.available()];
            inputStream.read(bytes, 0, inputStream.available());
            return new ResponseEntity<Object>(bytes, headers, HttpStatus.OK);
        } catch (Exception e) {
            //設置Content-type為application/json
            headers.add(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE);
            Map<String, Object> resultMap = new HashMap<>();
            resultMap.put("code", 500);
            resultMap.put("message", "not found");
            return new ResponseEntity<Object>(resultMap, headers, HttpStatus.OK);
        }
    }

也就是不使用RequestMapping的produces參數，改用ResponseEntity的特性來靈活定義返回header的Content-type，借此實現RESTful接口的定義。