一、背景

有个需求是这样的，客户端直接通过外网访问oss获取图片需要额外付费，考虑到成本问题，修改技术方案为：客户端将请求链接发给后端，后端根据请求做一定的截取或拼接，通过内网调用oss，再将下载下来的图片流返回给前端。

图片流，展现在页面上就是直接返回一张图片在浏览器上。

二、具体代码展示 

前端期望，如果异常，直接把http status返回非200

@Slf4j
@RestController
public class PictureController {@Autowiredprivate PictureService pictureService;@RequestMapping(value = "getPicture")public void getPicture(String path, HttpServletResponse resp) {boolean picSuccess;// 注意：一定要有这步，否则图片显示不出来resp.setContentType(MediaType.IMAGE_JPEG_VALUE);long start = System.currentTimeMillis();try {picSuccess = pictureService.getOssPicture(path, resp);if (!picSuccess) {resp.setStatus(HttpServletResponse.SC_FORBIDDEN);}} catch (Exception e) {resp.setStatus(HttpServletResponse.SC_FORBIDDEN);log.error("下载图片失败！！");}log.info("cmd=/getPicture,param={},cost:{}", path, System.currentTimeMillis() - start);}
}

public interface PictureService {boolean getOssPicture(String path, HttpServletResponse resp) throws IOException;
}

@Slf4j
@Service
public class PictureServiceImpl implements PictureService {@Value("${alioss.ak}")private String accessKeyId;// http://*********.aliyuncs.com@Value("${url.prefix}")private String urlPrefix;@Value("${oss.connect.time:3000}")private int ossConnectTime;@Overridepublic boolean getOssPicture(String path, HttpServletResponse resp) throws IOException {String url = getOssUrl(path);long st = System.currentTimeMillis();Request requestDownload = new Request.Builder().url(url).build();OkHttpClient client = new OkHttpClient();client = client.newBuilder().connectTimeout(ossConnectTime, TimeUnit.MILLISECONDS).build();Response responseDownload = client.newCall(requestDownload).execute();if (responseDownload.isSuccessful() && responseDownload.body() != null && responseDownload.body().byteStream() != null) {InputStream is = responseDownload.body().byteStream();writeImageFile(resp, is);} else {log.error("PictureServiceImpl-oss调用返回异常： url={}, data={}", url, responseDownload);return false;}long responseTime = System.currentTimeMillis() - st;log.info("request-oss cost:{}", responseTime);return true;}// base64解码==这块是与前端约定好的，我这边要做的解码private String getOssUrl(String path) throws UnsupportedEncodingException {final Base64.Decoder decoder = Base64.getDecoder();String decodePath = new String(decoder.decode(path), "UTF-8");StringBuffer buffer = new StringBuffer();String[] split = decodePath.split("&");for (int i = 0; i < split.length; i++) {if (!split[i].startsWith("Version")) {buffer.append(split[i]).append("&");}}log.info("getOssUrl={}", urlPrefix + buffer);buffer.append("OSSAccessKeyId=").append(accessKeyId);return urlPrefix + buffer;}/*** 将输入流输出到页面** @param resp* @param inputStream*/public void writeImageFile(HttpServletResponse resp, InputStream inputStream) {OutputStream out = null;try {out = resp.getOutputStream();int len = 0;byte[] b = new byte[1024];while ((len = inputStream.read(b)) != -1) {out.write(b, 0, len);}out.flush();} catch (IOException e) {e.printStackTrace();} finally {try {if (out != null) {out.close();}} catch (Exception e) {e.printStackTrace();}}}
}

三、总结

上面就是返回图片流的方式；

记录下！