使用HttpClient MultipartEntityBuilder 上传文件，并解决中文文件名乱码问题

遇到一种业务场景，前端上传的文件需要经过java服务转发至文件服务。期间遇到了原生HttpClient怎么使用的问题、怎么把MultipartFile怎么重新组装成Http请求发送出去的问题、文件中文名乱码问题。最后都解决了，先上代码，再讲遇到的坑

 @Slf4j
 @Service
 public class FileServiceImpl implements IFileService {

     @Value("${FileService.putUrl}")
     private String putUrl;
     @Value("${FileService.app_id}")
     private String appId;
     @Value("${FileService.securityKey}")
     private String secureKey;

     private final static String UPLOAD_RESPONSE_CODE = "error";
     private final static Integer UPLOAD_RESPONSE_SUCCESS = 0;

     @Override
     public String upload(MultipartFile file) {

         int timeOut = 30000;
         CloseableHttpClient httpClient = HttpClientBuilder.create().build();
         HttpHost proxy = new HttpHost("127.0.0.1", 62145, "http"); //设置本地fiddler代理，方便排查问题
         RequestConfig requestConfig = RequestConfig.custom().setConnectionRequestTimeout(timeOut)
                 .setConnectTimeout(timeOut).setSocketTimeout(timeOut).setProxy(proxy).build();
         HttpPost httpPost = new HttpPost(putUrl);
         httpPost.setConfig(requestConfig);
         try {
             //BROWSER_COMPATIBLE自定义charset，RFC6532=utf-8，STRICT=iso-8859-1
             //此处一定要用RFC6532，网上普遍用的BROWSER_COMPATIBLE依然会出现中文名乱码
             MultipartEntityBuilder multipartEntityBuilder = MultipartEntityBuilder.create().setMode(HttpMultipartMode.RFC6532);
             //multipartEntityBuilder.setCharset(Charset.forName("UTF-8")); //此处踩坑，转发出去的filename依然为乱码
            //ContentType contentType = ContentType.create("multipart/form-data",Charset.forName("UTF-8")); //此处也是坑，转发出去的filename依然为乱码
             multipartEntityBuilder.addBinaryBody("file", file.getInputStream(), ContentType.DEFAULT_BINARY, file.getOriginalFilename());

             multipartEntityBuilder.addTextBody("app_id", appId); //可替换成你自己需要的附加字段
             long time = System.currentTimeMillis() / 1000;
             multipartEntityBuilder.addTextBody("time", String.valueOf(time)); //可替换成你自己需要的附加字段
             String beforeSign = String.format("app_id=%s&time=%s%s", appId, time, secureKey);
             String sign = MD5Util.md5(beforeSign);
             multipartEntityBuilder.addTextBody("sign", sign); //可替换成你自己需要的附加字段

             HttpEntity requestEntity = multipartEntityBuilder.build();
             httpPost.setEntity(requestEntity);
             HttpResponse httpResponse = httpClient.execute(httpPost);
             int statusCode= httpResponse.getStatusLine().getStatusCode();
             if (statusCode != 200) throw new BizException(BizCode.INNER_SERVICE_ERROR, "响应状态码为：" + statusCode);
             HttpEntity responseEntity = httpResponse.getEntity();
             return getUrlString(EntityUtils.toString(responseEntity));
         } catch (Exception e) {
             log.error("发送文件异常：{}", e);
             throw new BizException(BizCode.INNER_SERVICE_ERROR, "发送文件服务异常:" + e.getMessage());
         } finally {
             try {
                 httpClient.close();
             } catch (IOException e) {
                 log.error("关闭httpClient异常：" + e.getMessage(), e);
             }
         }
     }

     private String getUrlString(String jsonString) {
         try{
             log.debug("解析json串："+ jsonString);
             JSONObject jsonObject = JSONObject.parseObject(jsonString);
             if (jsonObject.getInteger(UPLOAD_RESPONSE_CODE) != UPLOAD_RESPONSE_SUCCESS) {
                 log.error("文件服务返回错误：" + jsonObject.getString("data"));
                 throw new OtherServiceReturnErrorException("文件服务返回错误：" + jsonObject.getString("data"));
             }
             return ((JSONObject)jsonObject.get("data")).get("original").toString();
         }catch (Exception e) {
             log.error("文件服务返回json解析错误：" + jsonString);
             throw new OtherServiceReturnErrorException("文件服务返回json解析错误：" + jsonString);
         }

     }
 }

特别说明及遇到的坑：

1. 这里基于tomcat进行请求转发，需要在代码中手动添加代理：

HttpHost proxy = new HttpHost("127.0.0.1", 62145, "http"); //设置本地fiddler代理，方便排查问题
RequestConfig requestConfig = RequestConfig.custom().setConnectionRequestTimeout(timeOut)
        .setConnectTimeout(timeOut).setSocketTimeout(timeOut).setProxy(proxy).build();

2. MultipartFile通过getInputStream()可以将流设置到MultipartEntityBuilder中，其中addBinaryBody里面的ContentType 和 filename必须设置，要不然后续服务读取不到这个文件流

MultipartEntityBuilder multipartEntityBuilder = MultipartEntityBuilder.create().setMode(HttpMultipartMode.RFC6532);
multipartEntityBuilder.addBinaryBody("file", file.getInputStream(), ContentType.DEFAULT_BINARY, file.getOriginalFilename());

3. file.getOriginalFilename()方法虽然没有乱码，但是addBinaryBody后，组装的Http请求出去总是乱码，如下图：

踩了各种坑，如为MultipartEntityBuilder设置Charset或者是手动设置ContentType，都无法解决此问题，文件名依然是上图所示乱码

后来发现在MultipartEntityBuilder中设置Mode为HttpMultipartMode.RFC6532可以完美解决这个问题，并且不再需要单独设置ContentType或Charset，因为HttpMultipartMode.RFC6532就告诉了MultipartEntityBuilder，里面的数据都要使用UTF-8进行处理，fiddler抓到的请求发现filename成功变成中文名。

done