这两天老大突然交给一个任务，就是当用户关注我们的号时，我们应该将其微信头像下载下来，然后上传到公司内部的服务器上。如果直接保存微信头像的链接，当用户更换微信头像时，我们的产品在获取用户头像很可能会出现404异常。
由于公司运用的技术栈为 Cloud（一些Eureka, Feign）进行服务注册和远程调用。
重点来了。。。。但直接使用FeignClient去远程调用注册中心上的上传文件接口，会一直报错。
@PostMapping
@ApiOperation(value = "上传文件") public String fileUpload(@ApiParam(value = "文件", required = true) @RequestParam("file") MultipartFile multipartFile, @ApiParam(value = "usage(目录)", required = false) @RequestParam(value = "usage", required = false) String usage, @ApiParam(value = "同步(可选,默认false)") @RequestParam(value = "sync", required = false, defaultValue = "false") boolean sync) { if (multipartFile == null) { throw new IllegalArgumentException("参数异常"); } String url = map.get(key).doUpload(multipartFile, usage, sync); return UploadResult.builder().url(url).build(); }远程的上传文件的接口。
@FeignClient("dx-commons-fileserver")
public interface FileServerService { @RequestMapping(value="/file", method = RequestMethod.POST) public String fileUpload( @RequestParam("file") MultipartFile multipartFile, @RequestParam(value = "usage", required = false) String usage, @RequestParam(value = "sync", required = false, defaultValue = "false") boolean sync);}普通的FeignClient远程调用代码。但是这样的实现，在去调用的时候一直抛异常：MissingServletRequestPartException，"Required request part 'file' is not present"
这里去跟踪：fileServerService.fileUpload(multipartFile, null, true)源码发现发送的url是将multipartFile以url的方式拼接在query string上。所以这样的调用肯定是不行的。
那从百度搜索了一下关键词: feign upload 会看到有这样一种解决方案：
(原文转自:http://www.jianshu.com/p/dfecfbb4a215)
maven
io.github.openfeign.form feign-form 2.1.0 io.github.openfeign.form feign-form-spring 2.1.0
feign config
@Configurationpublic class FeignMultipartSupportConfig { @Bean @Primary @Scope("prototype") public Encoder multipartFormEncoder() { return new SpringFormEncoder(); } @Bean public feign.Logger.Level multipartLoggerLevel() { return feign.Logger.Level.FULL; } } feign client
@FeignClient(name = "xxx",configuration = FeignMultipartSupportConfig.class)public interface OpenAccountFeignClient { @RequestMapping(method = RequestMethod.POST, value = "/xxxxx",produces = {MediaType.APPLICATION_JSON_UTF8_VALUE},consumes = MediaType.MULTIPART_FORM_DATA_VALUE) public ResponseEntity ocrIdCard(@RequestPart(value = "file") MultipartFile file); }
这种方案很好很强大，照搬过来就很好的解决了问题。也实现了文件上传的远程调用。
但是问题又来了。因为上面的成功是很大一部分源于那个配置类，里面的Encoder Bean。但我的这个项目里不止需要远程调用上传的接口，还需要调用其他的接口。这样的话会发现其他FeignClient一调用，就会抛异常。真的是一波未平一波又起。心碎的感觉。跟踪源码发现：
SpringFormEncoder的encode方法当传送的对象不是MultipartFile的时候，就会调用Encoder.Default类的encode方法。。。。。。。。。。。
public class SpringFormEncoder extends FormEncoder {
private final Encoder delegate; public SpringFormEncoder () { this(new Encoder.Default()); } public SpringFormEncoder(Encoder delegate) { this.delegate = delegate; } @Override public void encode(Object object, Type bodyType, RequestTemplate template) throws EncodeException { if (!bodyType.equals(MultipartFile.class)) { delegate.encode(object, bodyType, template); return; } MultipartFile file = (MultipartFile) object; Map<String, Object> data = Collections.singletonMap(file.getName(), object); new SpringMultipartEncodedDataProcessor().process(data, template); }}而这个Encoder.Default的encode方法判断传送的类型不是String或者byte[]，就会抛异常：
class Default implements Encoder {
@Override public void encode(Object object, Type bodyType, RequestTemplate template) { if (bodyType == String.class) { template.body(object.toString()); } else if (bodyType == byte[].class) { template.body((byte[]) object, null); } else if (object != null) { throw new EncodeException( format("%s is not a type supported by this encoder.", object.getClass())); } } }
就这样，我又得继续寻找其他的方法，不然没法远程调用其他的服务了。这就很尴尬。
那接下来就是各种FQ，各种谷歌，终于找到了合适的答案。
原文转自（https://github.com/pcan/feign-client-test 可将示例代码下载下来研究，这样方便看调用的逻辑）
Feign Client Test
A Test project that uses Feign to upload Multipart files to a REST endpoint. Since Feign library does not support Multipart requests, I wrote a custom that enables this feature, using a HttpMessageConverter chain that mimics Spring's RestTemplate.
Multipart Request Types
A few request types are supported at the moment:
- Simple upload requests: One
MultipartFilealongwith some path/query parameters:
interface TestUpload { @RequestLine("POST /upload/{folder}") public UploadInfo upload(@Param("folder") String folder, @Param("file") MultipartFile file); } - Upload one file & object(s): One
MultipartFilealongwith some path/query parameters and one or more JSON-encoded object(s):
interface TestUpload { @RequestLine("POST /upload/{folder}") public UploadInfo upload(@Param("folder") String folder, @Param("file") MultipartFile file, @Param("metadata") UploadMetadata metadata); } - Upload multiple files & objects: An array of
MultipartFilealongwith some path/query parameters and one or more JSON-encoded object(s):
interface TestUpload { @RequestLine("POST /uploadArray/{folder}") public List uploadArray(@Param("folder") String folder, @Param("files") MultipartFile[] files, @Param("metadata") UploadMetadata metadata); }
根据上面的示例代码的提示，我也就按照上面的修改我的代码。因为原理方面没有深入的研究，所以很多代码直接复制过来修改一下。其中有一段：
Feign.Builder encoder = Feign.builder()
.decoder(new JacksonDecoder()) .encoder(new FeignSpringFormEncoder());这里的encoder是示例代码自己定义的（本人的代码也用到了这个类），decoder用的是JacksonDecoder，那这块我也直接复制了。然后修改好代码为：
@Service
public class UploadService { @Value("${commons.file.upload-url}")private String HTTP_FILE_UPLOAD_URL;//此处配置上传文件接口的域名(http(s)://XXXXX.XXXXX.XX)public String uploadFile(MultipartFile file, String usage, boolean sync){ FileUploadResource fileUploadResource = Feign.builder().decoder(new JacksonDecoder())
.encoder(new FeignSpringFormEncoder()).target(FileUploadResource.class, HTTP_FILE_UPLOAD_URL);return fileUploadResource.fileUpload(file, usage, sync);}}
public interface FileUploadResource {
@RequestLine("POST /file")String fileUpload(@Param("file") MultipartFile file, @Param("usage") String usage, @Param("sync") boolean sync);}
其中调用上传文件的代码就改为上述的代码进行运行。但是这样还是抛了异常。跟踪fileUploadResource.fileUpload(file, usage, sync)代码，一步步发现远程的调用和文件的上传都是OK的，响应也是为200.但是最后的decoder时，抛异常：
unrecognized token 'http': was expecting ('true', 'false' or 'null')
只想说 What a fucking day!!! 这里也能出错？？心里很是郁闷。。。。没办法，这个方法还是很厉害的，因为不会影响其他远程服务的调用，虽然只是这里报错。那只有再次跟踪源码，发现在JacksonDecoder的decode方法：
@Override
public Object decode(Response response, Type type) throws IOException { if (response.status() == 404) return Util.emptyValueOf(type); if (response.body() == null) return null; Reader reader = response.body().asReader(); if (!reader.markSupported()) { reader = new BufferedReader(reader, 1); } try { // Read the first byte to see if we have any data reader.mark(1); if (reader.read() == -1) { return null; // Eagerly returning null avoids "No content to map due to end-of-input" } reader.reset(); return mapper.readValue(reader, mapper.constructType(type)); } catch (RuntimeJsonMappingException e) { if (e.getCause() != null && e.getCause() instanceof IOException) { throw IOException.class.cast(e.getCause()); } throw e; } }
其中走到： return mapper.readValue(reader, mapper.constructType(type)); 然后就抛异常啦。郁闷啊。最后不知道一下子咋想的，就尝试把这个decoder删除，不设置decoder了。那终于万幸啊。。。。全部调通了。。。。。。。所以修改完的UploadService代码为：
@Service
public class UploadService { @Value("${commons.file.upload-url}")private String HTTP_FILE_UPLOAD_URL;//此处配置上传文件接口的域名(http(s)://XXXXX.XXXXX.XX)public String uploadFile(MultipartFile file, String usage, boolean sync){ FileUploadResource fileUploadResource = Feign.builder() .encoder(new FeignSpringFormEncoder()) //这里没有添加decoder了.target(FileUploadResource.class, HTTP_FILE_UPLOAD_URL);return fileUploadResource.fileUpload(file, usage, sync);}}
写这篇博客是因为这个问题花费了我一天多的时间，所以我一定得记下来，不然下次遇到了，可能还是会花费一些时间才能搞定。不过上面提到的示例代码还真的是牛。后面还得继续研究一下。
希望这些记录能对那些和我一样遇到这样问题的小伙伴有所帮助，尽快解决问题。